.

Andrew Connector L5NF

2011-09-23T08:42:00.004+07:00

For Sale

Andrew Connector L5NF (Heliax 7/8')
NOS (New Old Stock)

08811350050

Andrew Connector L5NM

2011-09-23T08:37:00.002+07:00

For Sale

Andrew Connector L5NM (Heliax 7/8')
NOS ( New Old stock)
08811350050

Simple SSB Receiver

2011-09-22T21:44:00.000+07:00

Simple SSB Receiver

7 Mc CW Transceiver 3 tr

2010-10-06T13:53:00.000+07:00

Pre amp GaAs FET

2010-09-30T08:12:00.000+07:00

Linear Amplifier with IRF830

2010-09-30T08:08:00.000+07:00

Antenna Colinear 915 Mhz

2010-09-30T08:03:00.000+07:00

Power Supply 20 A

2010-08-03T08:21:00.001+07:00

LM 386 74 dB

2010-07-29T09:33:00.001+07:00

LM386 is very popular IC also in Japan. It is used in Radio receiver. The power of it (500mW) is enough for the personal use. But sometimes, the gain of it (40dB) is not enough. Especially the direct conversion receiver depend on all of its gain on the audio amplifier. And therefore, we must stay sometimes the pre-amplifier before LM386. I will show you the way to get the 74dB only with LM386. Please watch the circuit ! Rf is the feedback control resister. By chanbeing the Rf you can tune the gain of this circuit as follows.

Rf (ohm)	gain
feedback resister	dB
3.3	74
10	70
33	54
105	44
820	34

--Emailer_-1249716426 Content-Type: text/plain; charset="iso-8859-1" Content-transfer-encoding: quoted-printable
Dear Sunamura-san, I like to read your web-site very much, and I repeated some of your constructions. I especially like your LM386 70 dB AF amplifier which I called =B3the Sunamura amplifier=B2 in our national Ham Magazine. Now, I have some news for you. The other day I found in our national ham magazine a new type of a rock stable VFO. They did not mention the first inventor, but I will try to find out who it was. It is a =8CColumbus= =B9 egg=B9 and it can substitute syntesizers. It uses a CERAMIC RESONATOR, and the frequency can be spread for about 100 kHz. I attach the electric diagram. The chief part s are the Ceramic Resonator CR and the variable capacitor C1. I used a standard CR for 3.579 kHz which is used as a clock in American digital devices. After a short warm-up, when you turn the capacitor C1 you can change the frequency for about 150 kHz - from 3440 to 3620 kHz. To cover the CW segnment of the 80 mteres band a variable capacitor of 140 pf is enough. And the frequency is rock stable. The capacitors C2 and C3 must have a capacity similar to the own capacity of the CR. In my case it was 600 pF. I also tried the ceramic filter for 10,7 MHz with three pins, but then I had to use 50 pF for C2 and C3, because that was the capacity of the filter. I used only two pins: the middle one and a side one - The frequency was between 10,9 and 11 MHz and the stability was very good. I also tried a 5,5 MHz filter, but it did not work well - it gave a frequency of 17 MHz with only 10 kHz of spread. I am sure that you will make use of this oscilator - with your tehcnical ingenuity. When I get some new CRs, I will make some more experiments. Meanwhile, I remain with best wishes, Bozidar Pasaric, 9A2HL, City of Rijeka, Croatia, Europe My E-mail: bpasaric@mac.com

Created by JF1OZL

One Transistor DSB Transmiter

2010-07-20T10:26:00.001+07:00

One transistor TX (50MHz DSB)...1trtxph.gif

I challenged to make very simple transmitter. It is constructed with only one transistor. It makes DSB signal. It can make QSO with normal SSB station. ***
See fig 1! Carbon microphone modulates 50MHz CW signal. It produces a double sideband signal. It pass through the 50MHz band pass filter. It is radiated by the antenna. ***
See fig 2! Modulator is constructed by diode single balanced mixer. ***
See fig 3! This machine is transmitter. Therefore I must use another transceiver in order to receive the report from my QSO friends. ***
See the table! With this machine I made four QSO's with friends living 50Km distance from me.

Table1: result of one night local expedition by this transmitter. All QSO was mwde on 18 Dec 1993.

time(JST)	QTH of contact station	distance(km)	Report receiv	memo
2121	Kumagayacity	67	41	Not good signal.But recognized.
2140	Kawaguchicity	57	34	Only call sign was copied.
2205	kazocity	47	45	He could hear that I say " Carbon mic is used".
2215	Kakegawacity	57	45	Small beet was heard. Carbon mic was heard.

Created By JF1OZL

Windom Antenna

2010-02-05T09:24:00.000+07:00

El Silbo

2010-01-27T06:37:00.000+07:00

Please click here to download the schematic

This double-sideband (DSB) radiotelephone transmitter is powered entirely by the instantaneous (not stored) energy produced in the operator's voice. The RF output power in my prototype falls within the range of 5 to 15mW. The circuit is essentially a high-level DSB modulator/crystal-controlled RF oscillator.

To date, my best DX QSO with this radio stands at 160km/100 miles (please see the station log below).

Please click here to hear El Silbo on W1TXT's receiver, located near Hartford, Connecticut; a distance of 245km (152 miles). This recording was made at 1800Z, or 1400 local time. The QRN level was high, the propagation was poor at this time of day and there is distortion in the audio (I also had a rock in my shoe :o)

I'm saying, "CQ CQ AA1TJ Voice Powered Transmitter 5mW." I know it doesn't sound like much, but please bear in mind the signal that you hear was projected 245km by the instantaneous power of my voice. A comment about this recording posted to Bill, N2CQR's, Solder Smoke Blog made me smile.

"The audio samples are eerie; remind me of those audiograms recorded back in the 1860s...you know, the woman singing the French folksong snippet..."

Thank you, Roberto. Oh yes, I know the clip that you're referring to. You can hear it here.

10/26/09; This afternoon I substituted an electret microphone (salvaged from an old telephone) directly driving an LM386 audio frequency amplifier in place of the voice-driven "loudspeaker" (SP1) shown in the above schematic diagram. This produced a peak DSB output power of 100mW (50mW in each sideband). I worked four stations on 75m this evening with this setup. Please click here to hear a recording of my signal made by W1PID (thanks Jim!) at a distance of 109km (the louder signal that you hear at the end is Seabury, AA1MY).

Circuit Operation

Speaking into the permanent magnet loudspeaker, an audio frequency alternating current will appear at the secondary winding of transformer, T1. When the signal on the upper end of this winding turns positive, diode D1 will become reverse-biased (effectively disappearing from the circuit). At the same time diode D2 will become forward-biased, and thus clamp both the collector of Q2 and the lower end of the primary of transformer T2, to ground. The Colpitts crystal oscillator - centered around Q1 - will begin to oscillate (the Colpitts capacitive divider consists of C6 and the active transistor's internal base to emitter capacitance).

When the audio frequency signal reverses polarity, Q1 becomes "clamped-off" and RF oscillation will commence in the Colpitts circuit, now centered around transistor Q2. An identical amplitude, but 180 degree phase-shifted, RF signal will appear on the secondary of transformer T2; as it must to insure proper DSB modulation.

Look Ma...No String!

El Silbo takes its name from Silbo; a whistled language (of sorts) that's used on the isle of La Gomera (Canary Islands) to communicate across wide mountain valleys. The best DX is apparently 2 miles, or just over 3km.

Some History

The idea for a voice-powered radiotelephone transmitter appeared not long after transistors first became widely available (my thanks to Roger, G3XBM, for unearthing this!). I wonder what became of Mr. Bryan's AM radiotelephone transmitter?

Time Magazine (October 17, 1955)

"The Army Signal Corps has developed a radio transmitter that needs no energy except electricity generated by the speaker's voice. The trick would be impossible if the set used vacuum tubes, but all it has is a single transistor, which needs only a faint current. When the speaker's voice makes the microphone vibrate, it generates enough current to operate the transistor and put the voice on the air. The present model, small enough to fit in a telephone mouthpiece, can transmit 600 ft. Later models, says George Bryan, developer of the set, should be good for a full mile.

Next step will be to build a voice-powered receiver. It will store up voice-electricity while the speaker is talking, then use it to pick up the answer while he is listening. Bryan believes that the entire outfit can be tucked into a plastic container no bigger than a matchbox. Mass-produced cost: $20."

Please click here to view a photograph of George Bryan and his voice powered transmitter which appeared in the December 1955 issue of Popular Science Magazine. You may also click here to download the United States patent issued to Mr. Bryan for this device.

El Silbo Logbook

Date Station His/Mine QTH Distance My Power Comments

10/13/09 W1VZR 57/459 Limerick, ME 160km 2.5mW Early ckt; resorted to "mouth CW"

10/22/09 AA1MY 57/33 Bethel, ME 160km 5mW 1st skywave voice-pwr fone QSO!

10/22/09 W1PID 59/54 Sanbornton, NH 109km 5mW Horrendous QRN; Fabulous QSO!

Links

http://www.physorg.com/pdf147367357.pdf

Home de AA1TJ

Aquarius 3.5 Mc CW Transceiver

2010-01-27T06:20:00.000+07:00

VU3PRX Transceiver

2010-01-16T09:35:00.000+07:00

Tube AM Transceiver

2010-01-03T21:42:00.000+07:00

Homebrew Radio Transceiver VK3YE Demo

2010-01-01T01:28:00.000+07:00

http://www.youtube.com/watch?v=BMLdhl0UdS4

Inverter DC to AC 500 W

2010-01-01T01:05:00.000+07:00

Switching PC Modification

2009-12-29T14:32:00.000+07:00

DO NOT TRY TO DO THIS MOD !!! IF YOU ARE NOT AWARE OF THE SHOCK RISK !!!

I got two old PC powersupplies for free, to be used for this test..
They are named DTK Computer model PTP-2008. 200 Watt Output.
Original outputs are:
+5V 20A
+12V 8A
-5V 300mA
-12V 300mA

After modification:
+13.5V 14Amp cont. 20 A for 20 sec.

The external 230 Volt AC power ON/OFF switch is removed and bypassed.
Old unused outputs are removed. Over voltage protection changed to only protect one output at 16 V,
Voltage regulating resistor net changed to only monitor a single output,

Do it like this:
Cut: white, orange, blue, and yellow wires as close as possible to the pcb.
Cut: all plugs away in the other end of the black and red wires, parallel all red and black wires..
Desolder: Fan wires, L1, L3, L4, R25, R26, R27, R29, R50, R51, R52, R61, R66, D10, D16, D17, C29, C28, ZD1
Mount a 680 Ohm 1/4 Watt at R50 location.
Mount solderpins in the holes for R26, R61 and Fan connection.

This is a fast part-drawn schematic that only covers what I wanted to know.
Mount 13.5 K Ohm at the solderpins at R26. (13.5 Volt output adjust point)

Mount 15 V Zener and 100 Ohm in series in the ZD1 holes. (Over voltage protection)
If two or more powersupplies needs to be paralled, then cut R30,
now it is possible to enter constant current mode opperation without shutting down.
This is also needed if your load (or radio) has big capasitors in parallel with the power supply line.

Orange wire connects unused cap to the new 13.5 Volt output (old +5 Output).

The fan is reverse mounted so that it will blow cold air into the heatsinks and transformer.
The NTC is glued with epoxy to the heatsink with the powerdiode,
The fan controller is changed so that the fan starts to rotate at +40 C on the heatsink,
If the temperature goes further up, the fan will rotate faster.

Mount potentiometer 47 K at R61 solderpoints. (adjust to fan start at 40 C then change to normal resistor)

Output ripple is under 5mV pp at 20 Amp. (0 - 100 Mhz)
I have tested it with my HF VHF and UHF rig, and could not hear any more noise than usual.
Output power has been tested with 14 Amps cont. for one hour, no problem at all !!
Efficiency at full max load is 60 %

This mod done April 2002 by me OZ2CPU.
Dont ask for schematics or any more info. All I have is here on this page..

Idea to this mod was found here:
www.qrp4u.de

If you want to know more about switchmode converters get the "bible" called:
Switchmode power supply handbook by Keith Billings. From McGraw-Hill Company ISBN: 0-07-006719-8

Homebrew Regenerative Receiver

2009-12-28T13:54:00.000+07:00

Homebrew Regen
Shortwave Receiver
Craig LaBarge, WB3GCK

Shortwave radio is what got me interested in this radio stuff in the first place. Ever since I was a kid huddled in front of an old console radio my grandmother gave me, I've been fascinated with the notion of listening broadcasts originating half-way around the world. I even had one of those SWL "callsigns" that a national SWL club used to issue. (My call was WDX3IYJ.)

Somehow over the years I had gotten away from SWLing. However, with the resurgence of interest in regenerative receivers in the QRP Community, my interest was peaked once again.

I had some free time one weekend and decided to try my hand at building one from scratch. Armed with an article by Paul Harden in QRPp, I raided my junk box and found that I had just about everything I needed to build one. Also, I decided that this would be a good project to build using Manhattan-style techiques I had been reading about.

The receiver I built was the "Pipsqueak." This little gem is based on an earlier regen design by Charles Kitchen with an improved audio section designed by Paul Harden. This little receiver is almost as simple as they get.

After a few hours of melting solder, I actually had a working receiver. The only problem I encountered was some oscillation when the volume was cranked all the way up. This was quickly resolved by added a .01 ufd capacitor across the output of the audio amp. Now it's rock-solid.

I mounted the circuit board on a small piece of pine and used a piece of copper-clad circuit board material for the front panel. The coil in the tuning section is wound with #22 hookup wire on a plastic 35mm film container.

I also did a little fiddling with the tuning section to get the band coverage I was interested in. I wound up putting a .001 ufd cap in series with the 140 pF poly variable tuning cap. It tunes from 4.9 - 10.3 MHz, covering 2 or 3 of the more popular shortwave broadcast bands.

The performance is surprisingly good for such a simple receiver. With a 20-foot wire antenna strung through the ceiling joists of my basement shack, I'm able to pull in the major shortwave stations with plenty of volume in the headphones.

Although I no longer chase QSL cards from the stations I hear, I still like to fire up this little radio and listen to the news from BBC. What makes it even better is knowing that I'm listening to it on a radio I built from scratch.

The magic is back!

Regenerative Receiver for 6 Mc - 17 mc

2009-12-24T09:23:00.000+07:00

Simple AM Radio Receiver

2009-12-22T09:32:00.000+07:00

50 Mc Transceiver JN3WVM

2009-12-17T06:43:00.000+07:00

5 Transistor RX FM 144 Mc JF1OZL

2009-12-17T06:36:00.000+07:00

5 transistor 144MHz FM receiver

In order to hear the 2m FM band, I made a simple radio.
In these days I began to use the transistor having ft over 1GHz. They can make gain over 40dB when they are used on IF amplifier. They can oscillate over 100MHz direct. Can you believe that? You can believe that when you make this machine. This machine is a simple single conversion receiver. Oscillator is made with varicap in order to avoid the body effect. This oscillator makes small QRH. But as a radio for SWL, It do not makes any problem.
Mixer convertor is made by dual gate FET. This is a basic usage of circuit of this FET transistor.
IF amplifier has 40dB gain only with 1 transistor. FM detector is called as Wise detector. The characteristic is shown on the fig.3.
The output impedance of Wise detector is very high. Therefore the input impedance of an audio AMP must be very high. Therefore I used a FET , on the front of the audio AMP. This AMP uses a very good output transformer named ST-47. Therefore the frequency characteristic of it is very good. See fig 4! This amplifier has 50mW power output. It is enough for the headphone.
I have jointed the antenna for this gear. I could hear the QSO on my city inside and that of nearby towns.

From: Mohan Mathew[SMTP:lisieux1@sancharnet.in] Sent: Tuesday, July 17, 2001 16:32 To: jf10zl@intio.or.jp Subject: Valuable Doubts! Hello Om.Kazuhiro Sunamura, I am a fellow SWL from India. I am contacting you the first time. I recently came across your home page and the valuable information*s about Ham radio Circuits. Thank you for all circuits and information*s, thanks a lot! I am studying for a graduate degree in Electronics here, I hope I will get the ham license soon(next month itself).I am listening the radio regularly all the bands except the 2meter band. This because I haven't any 2m radio. From your pages I got a 2meter circuit dia. I have some doubts about the circuit components. From the circuit dia its not clear that the converter FET no: clearly, I shall write the doubts for me about the components below.. 1.Converter FET no: 2.IF transistor no: 3.AF amplifier no(1&2): 4.Osc transistor no: 5.varactor diode no: 6.Toroid core no: 7.Is the o/p is an audio transformer?..etc.. please clarify the doubts for me...I think I can CQ you and all from here within 2 months. Can I write further email's regarding your circuits and articles? would you please give me a reply as soon as possible .... Thank you very much.. Mohan Mathew 7/17/01

Dear Mohan These transistors and coils are all famous in Japan. We can easy understand. But for the forliners it is not easy , I understood. I will explain farther more, with answering your question.
1.Converter FET no: 3sk60. Maker Hitachi. Usage VHR,RF amplifier. Pd=330mW. NF=2dB at 100MHz. Power gain=24dB at 200MHz. Please use double gate FET designed to use on the converter of VHF TV!
2.IF transistor no: All IFT are 455KHz AM radio usage. I do not know the number of it.
3.AF amplifier no(1&2): 1st 2sk327: I do not have detailed data now. Sorry! You can use any type of FET here. 2nd:2sc1740: Maker -Rohm. Usage=AF,RF,OSC,SW. Pc=300mW,hfe=120 to 820. FT=180MHz
4.Osc transistor no: 2sc2347: Maker = Toshiba. Usage = mixer. Pc= 250mW. FT=650MHz: Please use Silicone Epitaquisial transistor made to use on VHF mixer for VHF TV.
5.varactor diode no: 1S553: Please use varicap made for FM 80MHz radio converter!
6.Toroid core no: T50-10. Maker = Amidon.
7.Is the o/p is an audio transformer? : Yes. 600: 8 ohms Audio transformer . named as ST47 . Maker = Sansui.

RX FM 144 Mc PU2XJE

2009-12-15T08:59:00.000+07:00

BITX 14 Mc SSB Transceiver

2009-12-14T08:54:00.000+07:00

BITX SSB Transceiver for 14MHz

BITX is an easily assembled transceiver for the beginner with very clean performance.
Using ordinary electronic components and improvising where specific components like toroids are not available, It has a minimum number of coils to be wound.
All alignment is non-critical and easily achieved even without sophisticated equipment. The entire instructions to assemble the rig are given here along with relevant theory.

The Indian hams have often been handicapped by a lack of low cost equipment to get them on air. A mono-band, bidirectional design using ordinary NPN transistors was developed to cater to this demand. The design can be adapted to any particular ham band by changing the RF section coils and capacitors and the VFO frequency.

BITX evolved over one year from the excellent S7C receiver described in the new ARRL book �Experimental Methods in RF Design� (an ARRLpublication) into a bi-directional transceiver. Several hams across the globe contributed to its design. A series of emails were exchanged with OM Wes Hayward (W7ZOI) during the evolution of this design. His contributions have been invaluable. He urged me to strive for higher performance from the simple design. The resultant rig has sensitive receiver capable of strong signal handling, a stable and clean transmitter capable of enough power to make contacts across the World.

All the parts used in BITX are ordinary electronic spares components. Instead of expensive and hard-to-get toroids, we have used ordinary tap washers. Broad-band transformers have used TV balun cores. The entire transceiver can be assembled in India for less than Rs.300. I have designed a single side PCB with large tracks that can be easily etched at home or by any PCB shop. They are also available from OM Paddy, (VU2PEP, pepindia@yahoo.com).

For those who don't read long articles ...

There are a couple of things you should know before you start assembling the circuit:

The same amplifier block is used throughout. But the emiiter resistors vary in some of the places. Double check the values. If you swap values, the circuit won�t stop working. It will work terribly. That might be a little difficult to diagnose in the end. Check the emitter values and the resistors that go between the base and collector.
The receiving IF amplifier between the filter and the product detector is coupled to the product detector using a 100pf (not 0.1uf).
The crystal filter worked for me, I used crystals from the local market marked as KDS. These are the cheapest and they work with the capacitor values given in the filter. Your crystals might require a different set of capacitors. Try the values given here, if you find the bandwidth too narrow, decrease the capacitances, if you find it too open then increase the capacitances.
The microphone is directly coupled to the amplifier as my headset microphone needs 5V bias. If your microphone works without bias, then insert a 1uf in series with the microphone.
The pictures show my prototype on two boards. Don�t do that, split up the VFO into a separate box.
The pre-driver is built onto the main board. The driver and the PA are on a separate board. Keep the same layout to keep the PA stable.
There is a 50uf on the power line soldered near the BFO, don't forget it. It cleans up the audio noise which would otherwise get into the receiver.
On the PCB, there are jumpers between T lines and R lines across the ladder filter. There is a jumper from the BFO supply to the VFO suppl

Development Notes

Almost all modes of radio communications share a natural principle that the receivers and transmitters operate using the same line-up of circuit blocks except that the signal direction is reversed. The CW direct conversion transceiver is the simplest illustration of this principle. A more complex example is the bidirectional SSB transceiver.

Bi-directional SSB transceivers have been quite common in amateur literature. A transceiver was described in the ARRL SSB Handbook using bipolar transistors. W7UDM�s design of bidirectional amplifier (as the basis of bidirectional transceiver) is referred to by Hayward and DeMaw in their book Solid State Design. The bidirectional circuitry is often complex and not approachable by the experimenter with modest capability (like me).

The broad band bi-directional amplifier

My current interest in bidirectional transceivers arose after looking at an RC coupled bidirectional amplifier in the book Experimental Methods in RF Design (p. 6.61). An easily analyzed circuit that was simple and robust was required. It began its life as an ordinary broad-band amplifier:

In any bipolar transistor, the current flowing from the collector to emitter is a multiple of the current flowing from the base to the emitter. Thus, if there is a small change in the current flowing into the base, there is a bigger change in the current flowing into the collector. What follows is a highly simplified explanation of working of the above amplifier.

In the above circuit, imagine that a small RF signal is applied through R_in to the base of Q1. Also imagine that the R_f voltage is swinging up. The transistor will accordingly amplify and increase collector current causing more current to flow through the R_l (220 ohms) collector load. This will in turn drop the voltage at the collector. The drop in voltage across the collector will also result in a drop at the base (base voltage is a fraction of the collector voltage due to the way the base is biased). This circuit will finally find balance when the increase in base current flowing from R_in is balanced by the decrease in base current due to the voltage drop across R_l. In effect the RF current entering from R_in flows out through the feedback resistance (R_f). The impedance seen at the base is effectively very low and the signal source will see an approximate input impedance of R_in.

Thus, Vin/R_in = Vout/R_f (Eq.1)

Another factor to consider is that that emitter is not at ground. At radio frequencies, it looks like there is a 10 ohms resistor between the emitter and the ground. Thus, when the base voltage swings, the emitter will follow it. The AC voltage variations across the R_e (10 ohms) will be more or less the same as that across the base. The current flowing into the emitter will mostly consist of collector current (and very little base current). Thus, if the emitter current almost equals collector current,

Ie = Vin / R_e = Vout / R_l (Eq. 2)

We can combine these two equations to arrive at:

Vout / Vin = R_f / R_in = R_l / R_e. (Eq. 3)

This is an important equation. It means several things. Especially if you just consider this part:

R_f / R_in = R_l / R_e. (Eq 4)

Let�s look at some interesting things:

The voltage gain, and the input and output impedances are all related to resistor values and do not depend upon individual transistor characteristics. We only assume that the transistor gain is sufficiently high throughout the frequencies of our interest. The precise value of the transistor characteristics will only limit the upper frequency of usable bandwidth of such an amplifier. This is a useful property and it means that we can substitute one transistor for another.
The power gain is not a function of a particular transistor type. We use much lower gain than possible if the transistor was running flat out. But the gain is controlled at all frequencies for this amplifier. This means that this amplifier will be unconditionally stable (it wont exhibit unusual gain at difference frequencies).
You can restate the eq 3 as R_f * R_e = R_l * R_in . That would mean that for a given fixed value of R_f and R_e, the output impedance and input impedances are interdependent. Increasing one decreases the other and vice versa! For instance, in figure 1, R_f = 1000, R_e = 10, if we have R_in of 50 ohms, the output impedance will be (1000 * 10)/50 = 200 ohms. Conversely, if we have an R_in of 200 ohms, the output impedance will be 50 ohms!

In order to make bidirectional amplifiers, we strap two such amplifiers together, back to back. By applying power to either of amplifiers, we can control the direction of amplification. This is the topology used in the signal chain of this transceiver. The diodes in the collectors prevent the switched-off transistor�s collector resistor (220 ohms) from loading the input of the other transistor. A close look will reveal that the AC feedback resistance consists of two 2.2K resistors in parallel, bringing the effective feedback resistance to 1.1K. Thus, the above analysis holds true for all the three stages of bidirectional amplification.

Diode mixers

The diode mixers are inherently broadband and bidirectional in nature. This is good and bad. It is good because the design is non-critical and putting 8 turns or 20 turns on the mixer transformer will not make much of a difference to the performance except at the edges of the entire spectrum of operation.

The badness is a little tougher to explain. Imagine that the output of a hypothetical mixer is being fed to the next stage that is not properly tuned to the output frequency. In such a case, the output of the mixer cannot be transferred to the next stage and it remains in the mixer. Ordinarily, if the mixer was a FET or a bipolar device, it usually just heats up the output coils. In case of diode ring mixers, you should remember that these devices are capable of taking input and outputs from any port (and these inputs and outputs can be from a large piece of HF spectrum), hence the mixer output at non-IF frequencies stays back in the mixer and mixes up once more creating a terrible mess in terms of generating whistles, weird signals and distorting the original signal by stamping all over it.

A simple LC band pass filter that immediately follows the diode ring mixer will do a good job only at the frequencies it is tuned to. At other frequencies, it will offer reactive impedance that can cause the above mentioned problems. It is requirement that the diode mixer�s inputs and outputs see the required 50 ohms termination at all the frequencies. In other words, they require proper broadband termination. Using broad-band amplifiers is a good and modest way of ensuring that. A diplexer and a hybrid coupling network is a better way, but it would be too complex for this design.

Circuit Description

Although simple, every effort was made to coax as much performance as was possible given the limitations of keeping the circuit simple and affordable.

The Receiver

The RF front-end uses a triple band-pass filter for strong image and IF rejection. The three poles of filtering are quite adequate and the out-of-band response of the receiver is only limited by external shielding and stray pickups.

An RF amplifier follows the RF band pass filter (Q1) biased for modest current. More current would have required a costlier transistor. There is 8mAs through the RF amplifier and the post-mix amplifiers to keep the signal handling capacity of the circuit above average. The Post-mix amplifier (Q2) does the job of keeping the crystal filter as well as the diode mixer properly terminated. The crispness of the receiver is more due to this stage than anything else. An improper post-mix amplifier easily degrades the crystal filter�s shape and introduces spurious signals and whistles from the diode mixer. Note that the mixer is singly balanced to null out the VFO component and not the RF port and in the absence of proper pre-selection, 10MHz signals can easily break into the IF strip.

The VFO is fed via a broad-band amplifier into the singly balanced mixer. We used the simplest VFO possible with a two-knob tuning mechanism. It works really well and for those (like me) used to quick tuning, it offers best of both worlds, slow tuning through the varactor and fast tuning through the capacitor without any slow motion drive. Getting a slow motion drive is an increasingly difficult problem and this is an �electrical� substitute for slow motion drives.

A word about the VFO: depending upon component availability, skills and preferences, everybody has a favourite VFO circuit. Feel free to use what you have. Just keep the output of the collector of Q7 to less than 1.5 volts (it will appear clipped on the oscilloscope trace, that is okay). For 20 Meters operation, you will need a VFO that covers 4 to 4.4MHz. The given VFO has low noise though it does drift a little, but I have had no problems with ordinary QSOs. After 10 minutes of warm up, the drift is not noticeable, even on PSK31 QSOs.

A Hartley oscillator using a FET like BFW10 or U310 would work much better. You can substitute this VFO with any other design that you might want to use. If you are using the PCB layout, then skip the VFO on board if you want to use a different VFO and build it externally in a separate box.

The simple IF amplifier has a fixed gain. Earlier it was noted that IF amp was contributing noise at audio frequencies. It was later traced to noise from the power supply and placing a 50uf on the transceiver power line has cured it. The IF amplifier has a 100pf output coupling to provide roll-off at audio frequencies.

The BFO is a plain RC coupled crystal oscillator with an emitter follower. The emitter follower has been biased to 6V to prevent limiting.

The detector also doubles up as the modulator during transmit mode; hence it is properly terminated with an attenuator pad. It has no impact on the overall noise figure as there is enough gain before the detector. The audio pre-amplifier is a single stage audio amplifier. The 220pf capacitor across the base and collector provides for low frequency response.

The receiver does not have an AGC. This is not a major short-coming. Manual gain control allows you to control the noise floor of the receiver and I personally find it very useful when searching for weak signals or turning it down to enjoy the local ragchew.

Transmitter

The microphone amplifier is DC coupled to the microphone. This was done to steal some DC bias that is required when using a Personal Computer type of headset. If your microphone does not require any bias, then insert a 1uF in series with the microphone. The microphone amplifier is a simple single stage audio amplifier. It does not have any band pass shaping components as the SSB filter ahead will take care of it all. One 0.001uf at the microphone input and another at the modulator output provide bypass for any stray RF pickup.

The two diode balanced modulator uses resistive as well as reactive balancing. A fixed 10pf on one side of the modulator is balanced precisely by a variable 22pf on the other side. A 100 ohms mini preset allows for resistive carrier balance. The attenuator pad at the output was found necessary to properly terminate the diode modulator and keep the carrier leakage around the IF amplifier to a minimum. While this may seem excessive, it produces a clean DSB with carrier nearly 50db down with careful adjustments on the oscilloscope.

Rest of the transmission circuitry is exactly the same as the receiver. There is an extra stage of amplification (Q14) to boost the very low level 14MHz SSB signal from output of the microphone tip to driver input level.

The output amplifier boosts the SSB signal to 300mV level, enough to directly drive a driver stage.

The Power Chain

A simple power chain consisting of a low-cost medium power NPN transistor (2N2218) driving an IRF510 for 6 watts of power at 14MHz. The output of IRF510 uses a tap washer as an output transformer. The output transformer has 40 turns of bifilar winding; these can lead to enough stray capacitance to affect proper performance as a transformer. The half-wave filter that follows the transformer absorbs these capacitances as a part of the matching network.

I used this power chain because it works for me and delivers 6 watts on 14MHz. I don�t use more power because I neither require more nor do I have a power supply that can source more. If you need more power, there are a number of things that you can do, you can simply increase the supply voltage on the IRF510 up to 30 volts and extract nearly 15 watts of power from the same configuration. At 30 volts, the drain output will be at 30 ohms impedance and the pi-network will have to be designed to directly match the drain to a 50 ohms antenna load. Alternatively, you could try two IRF510s in push-pull. These are variations that you can play with. A word of warning though, The RF energy at these levels can give you a serious RF burn. RF burns can be more painful than fire or steam burns. QRP is not only fun, it is also safe.

Construction

I would highly recommend that you construct it over a plain copper clad board by soldering the grounded end of the components to the copper and the other ends of components to each other. Look at the pictures to see how it has been done. If you don�t know about this method of assembling RF circuitry, then you should read about it, there are quite a few write ups on the Internet about this method of RF experimentation. It does not require any PCB, it is quite robust and very stable.

Assembling the PCB

For those who feel intimidated by this �ugly� method, I have designed a PCB. The PCB layout (component side) is provided with this article. It is a single sided PCB with wide tracks that can be easily made in the home lab. I am making a run of these PCBs but shipping them abroad (outside India) maybe a problem. Drop a mail to me if you are planning to make some PCBs, I can put your contact information on the website. There are no copyrights over either the PCB, the circuit or even this article, feel free to copy and distribute.

The PCB is laid out in a long line.It is 8-1/2 inch long and 2-1/2 inch wide. The circuit board is big for the circuit that goes onto it. This was done so that the board is non-critical and it works well. All the bidirectional amplifiers are similarly laid out.

When you get your PCBs, inspect them thoroughly, preferable in the Sun. Check for small cracks in the tracks. Check for tracks that might be touching each other or touching the ground plane. The PCB layout was done to minimize this, but check it anyway. Especially check for the tracks that run diagonally to the base of each transistor in the bidirectional circuitry. These are laid out very closely and they are candidates for shorting.

Almost all assembly instructions ask you to solder the transistors in the end. I would highly recommend that you solder the transistors and the diodes first. You are most alert when you start a project and if you place the transistors correctly, the rest of the circuit can be soldered around it. Be very careful about the orientation of each transistor. The microphone amplifier transistor (Q10) faces in a direction opposite to the rest of the transistors and the transistor pairs in bidirectional amplifiers face each other. The diodes have a ring to indicate which way their �arrow� is pointing.

After the transistors are soldered, finish the BFO. If you are assembling this for 14MHz and above, the BFO will need a coil in series with the crystal (USB mode), if you are need LSB operation, you will need a trimmer instead (see the schematic). Apply power to the BFO and you should be able to hear it on your Short wave broadcast radio around 31 meter band. It will sound like a silent radio station. It should be quite strong. Switching the BFO power supply on and off will help you identify your BFO signal on the radio. If you have an RF probe, or an oscilloscope, you should be able to see the oscillations. Expect RF of 2 volts or more.

Next, assemble the VFO. Winding 150 turns of the VFO coil is one of the most tedious jobs while assembling this rig. It has to be done, so just dig in and do it. You don�t have to attach the 365 pf tuning capacitor yet. Check the oscillations on a receiver or a frequency counter. You may have to decrease the number of turns. Without the 365 pf, the 22pf trimmer should be able to set the VFO to 4.3MHz or so. If the VFO is oscillating at a lower frequency, then remove some turns from the coil. If the VFO is at a higher frequency, add 22pf in across the 22pf trimmer (if you are using the PCB, solder in from the foil side). You will require a wire jumper to carry power supply between the VFO and the BFO. They are the only stages that remain switched on during both transmit and receive.

Assemble the audio pre-amplifier and the audio power amplifier and attach the volume control. When power is applied to the audio stages, touching a finger to the base of Q4 should produce static in the speaker to move even the most die-hard trash metal rockers.

Next, assemble all the three bi-directional stages! This involves lot of soldering. But all the six stages are exactly the same. Finish one stage at a time. The capacitors are symmetrically laid out and all of them are 0.1uF with one exception (100pf at the output of Q3). Remember that the emitter bias resistors are 100 ohms, 220 ohms or 470 ohms. If you mix up the values, the rig will still work but it will under perform in the presence of strong signals and the transmission will be splattered. There are jumpers for T and R line across the crystal filter. Solder them up and power on the R line and then the T line alternatively. The emitters of bidirectional stages should show 2 volts approximately and the collectors should show around 8 volts and the switched-off transistor should show zero voltage on all the three leads.

For the moment of truth, solder the three coils, trimmers and capacitors of the RF filter, attach an antenna and switch it on! Check that the stages are working starting from audio end. If you touch the volume control�s control pin, you should hear AC hum and static. If you touch the base of Q4, there should be a pretty loud static. Take a lead from your VOM and touch Q3, you should get very loud static, probably mixed with local AM broadcast. Touch the base of Q2 with the test lead and you should get lesser static as the filter allows only 3 KHz of 10MHz through.

Finally, connect the antenna properly at the input of the RF band-pass filter and peak up the three trimmers for maximum atmospheric noise. Attach the 365 pf and start tuning around the band, peak the RF front-end on a strong signal and then tune in a weaker signal and peak for maximum clarity (not maximum sound).

An important note: Be sure that you have connected a proper 50 ohms antenna load. The RF filter performs correctly only at 50 ohms. If you use a long wire to do the initial testing, you will have to touch up the trimmers again for the proper antenna.

Take a break, spend the evening listening to your new homebrew. If the CW signals tune to dead beat and rise on the other side again, your BFO has to move its frequency. For USB, add more turns to the coil to the BFO coil, for LSB, tweak the trimmer. You should have a perfect single signal reception. If you tune past the dead-beat of a CW signal, the signal should drop out completely.

Assembling the microphone amplifier (Q10) and the output amplifier (Q14) will complete the exciter portion of the transceiver. To put the transceiver in transmit mode, ground the R line and apply 12V on the T line. Attach the output of Q14 to an oscilloscope but don�t attach the microphone yet. Null the carrier with the 100 ohms preset and the 22pf trimmer. Each affects the other so you might have to go back and forth between the two controls.

Now plug-in the microphone and speak into it. You should be able to see clean SSB of between 200 and 300 mV on the scope at the output of Q14. Instead of the oscilloscope you can use another 14MHz receiver to test your transmission quality. Switch off the AGC of the other receiver while setting the carrier null. A soft whistle (if you can manage) into the microphone is should result in a full carrier at the output.

Next, assemble the power chain. At this point, you will need a suitable chassis to house your project. Any metal box will do. If you don�t have any, you can solder pieces of copper clad together (like I did) and make a U shaped chassis. Keeping the VFO in open air makes it drift a bit. A closed box is really very useful.

A big cookie (or chocolate) box of tin is really ideal. With a hand drill, you can easily make holes to fit the two PCBs inside it. Tin is easily soldered on. Use the biggest knob you can find for the main tuning. The plastic broadcast capacitors usually have a very short stub that cannot take a big knob. It takes on a small plastic drum that is held onto the capacitor spindle with a retaining screw. Clip on the drum onto the tuning capacitor, tighten the retaining screw well and with epoxy glue, stick a big knob over the drum. This will make your main tuning mechanism.

I use a simple double pole triple throw switch for Transmit/Receive switch-over. If you prefer PTT operation, you can easily substitute the switch for a relay. Be sure to solder a reverse biased diode across the relay coil to prevent reverse voltage from entering into the transceiver power line.

Use shielded cable for all the connections between the power amplifier and the main board.

Tune-up and Operation

Set the VFO to correctly cover 4.0 to 4.4MHz. If you can, take your rig over to a ham friend�s shack, you can monitor your VFO on his rig at the edge of 80 meters band at 4.0MHz. Set the trimmer so that you can hear the VFO when the friend�s receiver is tuned to 4.0MHz and your tuning capacitor is fully closed (as much as it will go anti-clockwise). After this, connect the antenna and peak the RF coils for maximum noise in the speaker. If you can tune it to a weak signal, then peak the RF coils for best reception.

You might find that although you are able to tune in CW stations, you are unable to hear the SSB stations properly. This indicates that your BFO is not properly set. We will take that up next.

On amateur bands above 10MHz, SSB is transmitted on upper sideband and on bands below 10 MHz, it is transmitted on lower sideband. To tune a upper side-band signal, your BFO has to be at the lower edge of the crystal pass-band. You will require either the inductor (for USB) or the capacitor (for LSB) in series with the BFO crystal. If your BFO is set to proper frequency then the signals will tune in and as you continue tuning across the signal, they will drop in pitch and disappear. If the signals appear muffled, then the BFO is set in the crystal filter�s center, add more turns to the coil (USB), or tweak the trimmer (LSB). If the signals appear shrill and you are unable to zero-beat them, then the BFO is too far away from the filter�s frequency - Decrease the coil�s turns (for USB) or tweak the trimmer (LSB).

The transmitter tune-up essentially involves setting the carrier null. It is best to tune up the transmitter on a dummy load. I use 8 220 ohms, 2 watts resistors in parallel as my dummy load. It is worth the few bucks to have a proper dummy load. Attach the dummy load on the transmitter, and attach an RF probe to the dummy load (or an oscilloscope). As you speak, you should get 20 volts or more peak voltage on the dummy load when you whistle or just go �haaaaallow�. On another receiver in the same room, connect a short piece of wire as an antenna and monitor your own signal. You will probably be able to hear your own carrier as well. Null it by tweaking the 100 ohms preset and the 22pf balance trimmer. They both interact, so you might have to go back and forth between the two controls.

A word of caution, the diode mixers are prone to generating odd harmonics. The third harmonic of 4 MHz is at 12MHz. So, if you simply peak the coils for maximum output on transmit, you might wrongly peak the RF front-end to 12 MHz (I did that). The RF band-pass filter is best tuned in receive mode over a weak signal at 14.150MHz or so and left at that.

Conclusion

There might be a kit (components and the PCB in a bag) soon. I personally don�t have the time to put kits together. If somebody is interested in doing so, just go ahead and do it. The design is free, you don�t need to ask my or anybody else�s permission. If you can drop me a line, I will list you as a kit supplier on my site.

This is also the first time I have put out a PCB design for my rig. The purpose is to address the need among Indian hams in particular for an SSB rig that is easily and cheaply built. My original aim was to keep the price under Rs. 1000. The current design brings the cost to well under Rs.300 (less than 7 dollars). Contact OM Paddy (VU2PEP) for the PCBs. His email is pepindia12345@yahoo.com (I have added �12345� to confuse programs that automatically gather email addresses from my site, there is just �pepindia� before the at sign).

Loop Antenna VU3GAO

2009-12-11T08:44:00.000+07:00

HF/VHF Antenna Tunner De ON6MU

2009-12-10T09:58:00.000+07:00

L Meter N5ESE

2009-12-09T08:56:00.001+07:00

2 M Band Scope DH7GL - DF5FC

2009-12-08T18:41:00.000+07:00

SWR Meter HF VHF

2009-12-08T18:36:00.000+07:00

Simple Field Strength Meter

2009-12-08T18:31:00.000+07:00

Linearly Loaded Tee Antenna

2009-12-03T06:27:00.000+07:00

Linearly Loaded Tee Antenna

Tilted Folded Dipole Antenna

2009-12-03T06:23:00.000+07:00

Tilted Folded Dipole Antenna

THE ZZ "WAVE NET" ANTENNA BY VE6VIS

2009-11-30T06:22:00.000+07:00

A DUAL LOOP - 80 AND 40 METER HF WIRE ANTENNA PROJECT
When you can't go out, you've gotta go up!
Updated Sept, 2006 with new information
Do you want a full wave loop for 80 and 40 meters but have only a city lot?
Got a 64 foot tower or equivilant support with enough space at the top to add some insulators and a little time plus some wire? Got some 16 foot supports for each end? Want a great signal on both bands?
Then try this antenna project submitted by Mike Wigle, VE6VIS and prepare for loads of fun!

This antenna is the result of many hours of thinking and tweeking and trial and error and starting again and again. It was worth all the effort as I have come up with a very fine antenna that should make the lives of many hams much better by using a loop antenna instead of the inverted V's that so many of us use now.
The antenna is basically a full wave 80 meter loop on top and a 40 meter loop on the bottom all supported from a 64 foot center support, namely my tower. They are both fed from the center feed point with one length of 50 ohm coax. No tuner is required. Use the standard formula: 1005/freqmhz, (your center frequency), for total length of each "loop". Adjust for best swr by raising or lowering feed point from top of antenna. It requires the 64 foot center support (tower or mast) and 2, 16 foot end supports. VE6VIS
Editors note:
Another way of looking at this project is that two Delta loops, one for each band and squashed to fit the space on the tower and your lot are paralleled and fed with one length of coax.

The ZZ Wave Net is a revolutionary
new design in HF antenna's.
The ZZ Wave Net starts with
the same principal as a dipole
antenna bent into an inverted V.

Next, the ZZ is a folded dipole bent
into an inverted V loop!!!

Next we pull the ends of the folded dipole and separate
the middle as in the drawing above.
This allows us to install the antenna in a city lot and still
keep the overall performance of a full wave loop antenna!

Then we add the 40 meter ZZ loop under the 80 and we have the ZZ Wave Net, a dual 40 & 80 meter full wave loop antenna!

Below is how it looks installed on a 64 foot tower with 16 foot
end supports on your city lot.

Dimensions:
(80 meter on top, 40 meter on bottom)

80 meter apex to end 70 feet/ 21 m
80 meter end to feedpoint 65 feet/ 19.5 m
40 meter feedpoint to end 36 feet/ 10.8 m
40 meter end to bottom 34 feet/ 10.2 m

Apex to feedpoint 24 feet/ 7.2 m
Feedpoint to bottom 12 feet/3.6 m

Feedpoint is 4:1 balun
Both loops feed from this point

End support to end support 105 feet/ 31.5 m

Construction:
Measure wire and lay out at base of tower.
Attach 1 litre bottle half full of water to the bottom wire about 12 feet from the ends on both sides of antenna.This is so the wires don't twist and so the antenna will have greater tuning range.
Attach apex of antenna to top of tower on a standoff and preferably with a rope and pulley system.
Pull feedpoint up to 24 feet below apex.
Pull ends out to look like the picture.

Tuning Instructions
The wire length is the first thing to get right.
Use the usual method of (low longer) ie: if the swr is higher on the low freq then make the antenna longer and if the swr is higher on the high side then make the antenna shorter.
Then the next step is the distance between the wires.
The distance between the feed point and the apex is 24 feet @ 80 meters.
The final tuning is done by tightening the wires from the ends.

Tight ZZ

So you get the antenna pulled out to look like the
picture above, then you can adjust the swr by tightening and
loosening the wires. You will see a great range of
tuning here which is why this antenna design is so
easy to tune.

The best way to do this is to mark the place where the
rope meets the tie off point. ( this is the trick for
tuning this antenna) So, if for instance you have the
rope tied off to a tree. You mark the point where the
rope meets the tree by tying a piece of string onto the rope.
This is your marker.

Check the swr. Then loosen the rope so the marker is
about a foot from the tree, Then check the match again. You
will notice that it has changed. Now you can tune to a
point where the match is lowest.
Shorten and lengthen the wire to provide the lowest swr
within the range that you can loosen and tighten the wires
for lowest swr and you will find that this antenna will
match right down flat at the operating freq of your choice :)
Also you may find that the antenna wants to be shorter
than the normal calculation.This depends on a number of factors
like reflections and hieght above ground.

Tune the 80 meter length first and then the 40.
This antenna also works as an 80 and 20 or 80 stand alone,
40 stand alone, 40 and 20 etc.

Have fun :) Mike Wigle, VE6VIS
Russian Translation here
by UA3TJC

The EWE Antenna

2009-11-30T06:17:00.000+07:00

VHF Magnetic Loop ON6MU

2009-11-30T06:08:00.000+07:00

Antenna Trap WA7JHZ

2009-11-24T06:01:00.000+07:00

80 METER FRAME ANTENNA

2009-11-23T06:34:00.000+07:00

80 METER FRAME ANTENNA
by Harry Lythall - SM0VPO

http://web.telia.com/~u85920178/antennas/frameant.htm

I keep on and on about my little balcony and the antenna restrictions it imposes on my HF antennas. This projects was developed as a result of experiments to become QRV on 80 meters, again, using the little balcony. I have now built several of these antennas with equal success every time. The frame antenna may not be the most efficient but it can get you QRV on 80 and is ideal for boats and holidays. The VSWR is almost 1:1 from 3.5 to 3.8 MHz. The antenna may be modified for 1.8 MHz but the efficiency may suffer.

CONSTRUCTION

The construction of the antenna is shown above and is a five turn loop of one cable from 5 ampere mains cable. The cable must have a multi-stranded conductor. The antenna uses over 20 meters of the cable, so I stripped down 7 meters of 3-core cable and soldered the ends together. Construction is otherwise quite straight forward if you follow the above drawing. Note that all cable lengths shown are approximate.

The two boom poles - I have used both cane and a plastic clad tin (metalic) pipes, of the sort that are sold in garden shops. Both worked very well in spite of the difference in materials. If you do use metal booms then insert some form of insulation in the holes before you pass wire through them. I used plastic drinking straws from MacDonalds. This will prevent the metal from digging into the cable insulation, as well as improving the insulation.

With the dimensions shown each loop will be separated by 4cm. The natural capacity between the turns will tune the antenna to (about) 4.15 MHz, just above the 80 meter band. One of those Jackson 804 / 805 VHF tuning capacitors with about 25pf will tune the antenna down to 3.45 - 3.90 MHz. The tuning capacitor MUST be one with a couple of millimeters between the plates. The antenna has a very high Q so the voltage across the capacitor will be very high, even with small QRP powers.

160 METERS

A capacitor of 410 pf placed across the tuning capacitor move the antenna frequency down to 1.9 MHz. This capacitor MUST be a high voltage type. This antenna could get you QRV on 160 meters although efficiency is likely to suffer, but Ok for local nets and the like.

TRIMMING

If the 80 meter antenna does not naturally fall on 4.15 MHz, or the tuning capacitor is not centered on the band then some frequency adjustment can be made to the final antenna.

If the frequency is a little LOW and you need to increase it then some of the self capacity must be removed. Thread a bit of plastic tube between the wires of one side; IN, OUT, IN, OUT, IN. See '*1' in FRAMEANT.GIF. Repeat on more than one side of the frame antenna if a larger frequency increase is required. If the increase is still not enough then insert two tubes in each side and slide them apart to get a large increase.

If the frequency is too HIGH and you need to decrease it then some more capacity must be added. Connect a high voltage capacitor across the variable tuning capacitor. A short length of coaxial cable is ideal. Cut the coaxial capacitor shorter to reduce to the required capacity (increase the frequency). Do not be tempted to make a 'gimmick' capacitor with two wires twisted together; it will burn, even with a couple of watts of RF. This means that you have added more losses.

Have fun, de HARRY, Upplands Vasby, Sweden,

Broadband Transformers plus Mixers

2009-11-23T06:12:00.000+07:00

Broadband Transformers plus Mixers

There are 2 basic types of broadband transformers used in most QRP work, conventional and transmission line style. Both types can be wound on ferrite toroids, potcores or rods, however for this discussion we will confine ourselves to the toroidal types used to give a 4:1 impedance transformation. These transformers are used throughout the various projects on this website. For MF and HF uses, a ferrite core permeability of 850-900 is generally required and the FT37-43 ferrite core is suitable. This will allow AC circuits to transform from unbalanced 50 ohms impedance up to 200 ohms unbalanced impedance or visa-versa. Shown below are three equivalent schematics of the 4:1 transmission line transformer. The center drawing is the easiest to conventionalize, however close examination will show that all 3 schematics represent the same thing. The high impedance is 200 ohms and the low impedance is 50 ohms in all cases. It is important to know that these transformers are symmetrical and the points labeled Ground or VCC can be switched with the point labeled High Impedance. There are a great many published references on RF transformers for further study.

Winding the 4:1 Transformers

These transformers are wound as bifilar (2 wires) which are generally twisted together. Winding these transformers is very easy. All that is required is two 7 to 8 inch pieces of #28 AWG enamel coated wire and an FT37-43 ferrite toroidal core. A vise, ruler and a brace and bit drill are also very useful. I got my brace and bit drill at a garage sale for two dollars. You need to twist the 2 pieces of wire together so that there is around 8-10 twists per inch in the wire. To do this, loosely twist the wires at one end so they are of equal length. Place the twisted ends in a vise about 1/4 inch. Next, place the free wire ends together in your brace and bit drill chuck (no drill bit) and tighten up the chuck so that the wires are held secure. The wires should be of equal length and tension. Start hand winding the drill to twist the wires together and every once and a while use the ruler to check how many twists are in a one inch space. When you get to 8-10 twists per inch you are done and can trim the very tips with a wire cutter in preparation for winding.
You generally need somewhere ~ 7 inches of wire for winding a complete transformer. Leaving a 1 inch lead, wind ten complete loops through the toroidal core leaving a small gap between the start and finish leads.
Untwist the leads a little so that you have 4 separate wires. One set of these wires wires will be called winding #1 and the other winding #2. You need to identify them and further break them into 1a, 1b and 2a and 2b. Generally I regard the the top two windings as A and the the bottom two wires B. Use whatever system works for you. Strip off all the enamel on all four leads and then get your ohm meter or better yet a beeping continuity tester. Start on one of the top (A) wires by connecting the ohmmeter or continuity beeper to it and then touch one of the bottom wires and then the other bottom wire. Whatever bottom wire shows continuity with the top wire should be marked along with the source top wire with paint, liquid paper or whatever you like. Designate the marked wire pair winding number 1. You can test for shorts as well, there should be no connection between wire set 1 and wire set 2 at all! So now you have two wires sets, winding set 1 is marked and winding set 2 is unmarked. The top two wires are arbitrarily labeled A and the bottom two wires are labeled B . Refer to the diagram above for clarification. Connect 1b to 2a and twist them together and then solder. Your transformer is done. It is really easy to make these things. More elaborate methods such as using 2 color wire and painting one wire maybe used. These transformers will also work if the wires are untwisted, when you twist them, 8-10 twists per inch is a guide only and is not critical. Never use bare wire for these transformers.

Homebuilding Diode Ring Mixers

Discussion:

Homebuilt diode ring mixers are also easy to make and can be quite a cost savings. A doubly-balanced diode ring mixer has two unbalanced to balanced transformers and a diode ring. The impedances at the three ports is 50 ohms. The transformers are wound with #28 AWG enamel coated wire on a FT37-43 ferrite toroidal core using a trifilar (three wire) technique. The wire twisting and winding technique is done as described above for the bifilar transformers. The connections 2b and 3a are twisted together and soldered. Again you will have to develop a technique to help you distinguish the wires from one another.

Diodes

Discussion:

For optimal results Schottky or Hot-Carrier diodes should be used. However, common diodes such as the 1N914, 1N4148 or 1N4454 are all quite suitable and are much cheaper. The four ring diodes should be matched to help mixer balance and thus carrier suppression. At MF and HF the most critical matching required is the forward voltage drop across the diode and this is easily performed with a sensitive voltmeter. Set your voltmeter on the 2 volt scale to give you three decimal places for matching the voltage drops. Try and find 4 diodes close to one another. In addition, best results maybe obtained if all the diodes are the same type (ie. all 1N4148) and if they are all from the same manufacturer. Below is a easy schematic for matching your diodes with a voltmeter. Give the diode under test at least 20 seconds to warm up and stabilize before taking your voltage measurement.

VE7BPO

Ladder Crystal Filter Design

2009-11-20T18:31:00.000+07:00

John Hardcastle, G3JIR, described an interesting ladder filter design technique in 1980 that appears to have been forgotten. I've extracted the relevant information from John's article and presented it, somewhat simplified, in 'cookbook' form.

Basically, G3JIR's technique involves measuring the bandwidth of a simple two-pole filter, modifying it for the desired bandwidth, and then calculating the shunt capacitors required for a filter of the same bandwidth, but with more crystals to improve the shape factor.

The following test rig needs to be constructed. I just wired it up on a scrap of PCB material. Since the input and output impedance should be equal I used a dual pot. Separate ten-turn pots might make the settings easier if you want to get the resistance settings 'spot-on'. They aren't all that critical.

1. Using

               R1 = 0.613*1E6/(2*PI*f*C1)

calculate the test impedance (Ohms).

2. Set the filter input and output impedance on the test rig to this value, measuring between A-B and C-D using a DVM.

3. Sweep the signal generator across the filter pass-band. The ripple should be about 1 dB with two peaks. If it isn't you've either got the calculation wrong, or set the pots incorrectly.

4. Measure the 3 dB bandwidth (BW1).

5. Calculate C for the desired bandwidth (BW2), using

               C2 = C1*(BW1/BW2)^2.

6. Calculate the new impedance using

               R2 = 0.613*1E6/(2*PI*f*C2)

7. Change the coupling capacitors to C2, and set the input and output impedance to R2.

8. Measure the new bandwidth. It should now be BW2.

To be continued ...

References:

Hardcastle, J.A. Ladder Crystal Filter Design. QST. November 1980. Pages 20-23.

Crystal Filter 9 Mc

2009-11-20T18:17:00.000+07:00

Modifications for the Kenwood TH-78

2009-11-20T18:13:00.000+07:00

Basics of modifying the Kenwood TH-78a

To open the radio, follow the instructions on page 64 of the manual.
(Unscrew four screws and break apart the radio halves.) The two TX/RX busy indicators (LEDs) have rubber seals placed over them. These have a tendency to fall off when opening or closing the radio.

All position references in this document assume that you are looking at the CPU board with the rotary encoders and TX/RX busy indicators at the top.
If you have installed the ME-1 EEPROM, I recommend that you temporarily remove it to facilitate access to the diodes.

You'll see a brass shield about one centimeter square covering the processor chip and the surface-mount diodes on the back half of the radio.
De-solder the shield's four corners and remove it. (I used an right angle surgical tweezers in conjunction with the pin-point soldering iron to lift the brass shield.)

Uncovered are the processor (which we ignore) and six surface-mount diodes, numbered sequentially from one through six (D1 - D6), top to bottom. These are about one millimeter wide; remember the note about skill and finesse.
New model radios also have two large loops of green wire, numbered one through two (W1 - W2), bottom to top.

You'll need a pinpoint-tip soldering iron and some braid to wick away the solder before you lift out the diode. Alternatively, Rich Garcia (n2czf@wt3v.nj.usa) suggests leaving the diode in place. "I found if you BRIEFLY touch the iron to the right side lead while gently pulling up on the SMC diode it should completely come off without needing to apply heat to the other side and further risk board damage."

After you perform some or all of the mods listed below, replace the brass shield and re-assemble the radio. Then reset the processor (as documented) and re-enter any frequencies into memory.
Potential case design flaw

In the course of performing mods on my Kenwood TH-78a dual band handheld, I've discovered a potential flaw in the case design. While handling my walkie one day (after the mods were done), the display went blank and I could not turn the radio back on. With the radio split in half again, I could turn the radio back on but discovered all the memories were erased. The cause turned out to be some component pins on the front face coming in contact with the square bodies of the two volume/channel/squelch switches, when the case is screwed back together snuggly. I placed small strips of electrical tape on the sides of the switches to insulate, and reassembled; problem solved. Now I have to reprogram the darn thing....
molson@bml4380.cpg.cdc.com (Mark Olson) said:

There is a warning on some of the rig mod bulletin boards about this. The problem is that pins on the back side of the PCB that is mounted on the front half of the TH78 can come into contact with the volume control housings mounted on the PCB on the other half of the unit. My radio had this problem until I put electrical tape across these housings. Symptoms were: Display blanking momentarily and the unit power cycling, sometimes causing memory erase, when pressure was applied to the front of the unit or to the volume controls. I originally thought that it was a loose battery connection...

Open up the radio and you will see what I mean... Believe me, the fix is simple and it works.
C-17 design flaw

William_A._Kirsanoff@smtpgty.anatcp.rockwell.COM said:

"The 78A WILL lose C-17 on the control board if dropped, period. This causes loss on receive audio on the left-hand side of the radio. The solder pads for that cap are not big enough. If you find the need to replace C-17, use a gap-fill cyanoacrylate glue like Zap-A-Gap (tm) to increase the device footprint. I have learned the hard way.
Otherwise, I have found it to be a fine radio. My only problems have been related to the C-17 issue and attempts to rectify it. Had I been given the above advice, it would have been a one-time only issue. As it is, I took out one of the microprocessors yesterday looking for a bad solder joint that was induced by my attempt to solve the C-17 problem (sigh). This radio gets a lot of use and a lot of travel. C-17 is the only thing that I have broken with the case closed.
Mutually exclusive mods

Some of these mods are reputed to be mutually exclusive. You must choose one of the following levels of performance:

The "beyond MARS" mod - gets you the widest tx/rx
The "MARS/CAPS" mod - halfway there
The "extended receive" mod - more of a good thing

plus

The "cross-band repeat" mod - a repeater that weighs almost nothing
There is no mods that manipulate diodes D1 or D2 (I've seen it suggested elsewhere that this is toggles the USA/Europe-ness).

Brendan_Hoar@notes.pw.com suggests:

"I think removal of D1 causes "Forced Channelized Mode", at least on the "new" radios. If you put both VHF and UHF memories into a TH78A without D1 and power on, you are stuck in channel mode until you do a full memory reset. Remember, you can't add frequencies or do any tuning in channel mode.

If you think about it, you'll want to be very careful not to let D1's circut become an open circut.
The beyond MARS mod

This mod provides the widest possible range of tx/rx. The mother of all TH-78a mods.

To mod (early model): remove diode D5 only.

To mod (late model): remove diode D3 and cut wire W1. D5 has priority over D3, so if you've already made the mods for the old model (which included the removal of D5) you must resolder D3 into D5.

Yields RX 50-179.995, TX 136-179.995, RX 300-399.995, RX 400-511.995, TX 400-511.995, RX 800-999.995.

To use: buttons operate the same way as described in the "extended receive" mod, except that you can transmit on a much wider range.

NOTE TO ALL: I haven't been able to verify the actual operation of my radio on all these freqs. Kenwood talks about the difference between the "dialable" range and the operating range. I'd like to come up with a chart for each level of mod that combines the above and the two following offerings. Help me, please.

* * * * * * * * * * * * * * * * * * * * * * * * * * * *

        Left VFO                        Right VFO

50.000-85.2x (with beep)                50.000-110.xxx (with beep)

85.2x-179.995                   110.xxx-179.995

300.00-399.975

400.000-511.9875                400.000-511.9875

                                800.00-999.9875

* * * * * * * * * * * * * * * * * * * * * * * * * * * *

Receive                         Transmit

---------------                 ---------------

50-135.995 (AM)        VHF      (NA)

136-179.995             "       136-179.995

300-399 (AM & FM)       "       (NA)

400-511.99           SUB-UHF    400-511.99

400-511.99             UHF      400-511.99

900-949.9875            "       (NA)

50-179.995 (FM)      SUB-VHF    136-179.995

The CAP/MARS mod

This doesn't cover as much room as the beyond MARS mod does, but may be more appropriate for those who use the CAP or MARS frequencies.

To mod (both early and late models): remove D6 only.

Yields RX 118-173.995, TX 142-151.995, RX 400-511.995, TX 425-454.995.
The extended receive mod

This is the mod that's usually given to hams to pacify them (the beyond MARS mod is closely guarded).

To mod (both early and late models): remove diode D5.

To use: press "F" for one second and then pressing the Band button will switch the UHF VFO to a 800-999.995 MHz band and the VHF VFO to a 300-399.995 MHz band. The regular VHF VFO can now receive down to 50 Mhz.
The cross-band repeat mod

To mod: remove diode D4.

To use: press "F" for one second, then "0". Repeat to disable. The MHz dot will flash when in repeater mode.
Toggle SHIFT button function

Press SHIFT during power-up This is described in the manual, but the documentation is not complete. The TH-78A can operate in two modes: In SPLIT mode, non-standard offsets (i.e. split frequencies) are supported, but the default offset is not programmable. In SHIFT mode, non-standard offsets are not allowed, but the default offset is programmable. To select the default offset, press F for 1 second, then SHIFT. See p. 30 of the manual for details on changing the default offset.
Toggle CALL button function

Press CALL during power-up. The CALL button can operate in one of two modes. In the default mode (CALLSW), it switches between the call channel and the last memory channel (if in memory recall mode) or last frequency (if in VFO mode).
After toggling the CALL button functionality (VMC), it will switch from the VFO to the last memory channel and then back to the CALL channel.
Observations on post-mod performance

Rich Garcia (n2czf@wt3v.nj.usa) observes "all original functions have maintained the same which is great. Aircraft band which was accessible before the mod remains with the same characteristics. It seems that VHF-High band has improved a bit on sensivity where it was dead as a dog before the mod (above 155.000MHz) but the 162.000 MHz band where weather radio is is still a bit deaf for reception at any distance but about 20 Miles. This depends on your (or my) terrain and transmitter output power.

"On UHF all public safety frequencies up to about 500 MHz seem to come in well but sensivity greatly drops from there (we really can't ask for more).
Frequencies can be programed in up to the 920MHz ham band but I have no way of measuring sensivity. 800MHz works but the signals are very weak, you must be near the transmitter for reception. Assuming you are in the town or city where the transmissions originate it should work.

"Transmit is enabled up to and incl. 500MHz but after testing this on a frequency counter I find that a signal is only generated to about 490 MHz, even though the trans. LED shows output in the higher frequencies.

"Crossband repeat seems to work fine but the audio is unacceptable for use, BE AWARE the radio gets HOT! Prolonged use or use on a busy frequency would not be recommended. Also remember this is a dual band HT please use a proper antenna while in this mode to avoid a high SWR, we should all know better... Right?"

Someone else said:

"I found that marine weather reports at 162.40MHz in my area were received much better on the SUB-VHF band, than on the VHF band...

"If you are having problems with intermod, try switching bands (i.e. using the SUB-VHF band rather than the VHF band.)"
Cloning

The TH-78a's memory can be copied from one TH-78a to another TH-78a entirely through radio waves "over the air" (i.e. without cables or other special equipment). Theoretically, this could be done via repeaters, although I've never heard it done. Allegedly this requires a mod that includes removal of D5 or D6, but I haven't researched it.

Cloning is a real boon to groups that want a bunch of radios to contain the same memories, such as amateur radio clubs, search and rescue units, and people too lazy to program their radios. Of course, given that the ME-1 memory expansion unit has 250 memories, laziness is understandable :-)

Set both radios to the same frequency.
Activate both radios by pressing the '0' key while turning the power on. The radios will display the word "clone".
Now, click the PTT button of the "master" radio. The radio will transmit in the economy low power mode. This may take about 4 minutes for fifty channels, or 20 minutes for the 250-memory ME-1. When the data has been transferred, both radios will revert back to their original frequency.
(It is recommended that a dummy load be used to prevent unwanted interference.)
Turn both radios off and then on again. The slave is now a mirror-image of the master radio.

Cellular Telephones

Cellular phones operate at (tx) 824.040 - 848.970 (rx) 869.040 - 893.970, within reach of your modified TH-78a. The increments are, however, every 30kHz; the TH-78a will only increment in 25kHz steps at this frequency range, so the exact cellular frequency cannot be tuned in (most of the time).
Battery life on the TH-78A

wd6cmu@netcom.com (Eric Williams) says:

Some people have complained about the battery life on the TH-78A. I came up with these tips by checking out the power consumption under various configurations. In the case of power-saver mode, figuring out the average current with my DVM was impossible, so I ran the radio on a large capacitor and timed how long it took to die. These tips won't solve everything, but they might help.

The rig draws close to 2ma even with the power turned off, so don't leave the rig off with the battery installed for several days and expect full capacity to be maintained.

If you're only using one of the bands, shut down the other to extend your battery's life -- current consumption with the squelch closed is cut by almost a third.

If you're monitoring two frequencies on the same band, use the f2 button to receive both simultaneously rather than scanning between them -- the battery saver with two receivers will use about half the current of one receiver that is scanning.

You can make up a battery pack by putting nickel metal hydride AA cells in a BT-8 battery holder. A small strip of aluminum from the positive battery terminal to the depression in the top of the case will allow you to recharge the pack inside the rig. This will give you 1000mah capacity without enlarging the size of the radio, and NiMH cells have no memory effect. (But they *are* expensive.)
Game Mode

aviator@athena.mit.edu (who no longer exists), who credits
james@brokaw.lcs.mit.edu for "much of this".
To enter the game mode press M and PTT during power-up. Be careful not to accidentally reset the memory, which happens with M + power-up. (Don't freak; you'll see the same "all screen items lit" when entering game mode as when you reset memory.) To exit the game mode at any time, press the LAMP key. The volume, lamp, or frequency settings can't be changed while in game mode.

The top part of the display will show "H.00", which represents the high score. The lower part shows a scrolling message, "PRESS ANY KEY". Pushing any key starts a "Follow Simon" type game. The display will briefly show one of the characters '1', '2', '3', or 'F'. Press the corresponding key. The game consists of repeating the displayed character sequence, which increases by one character each round.

After you "win" the Simon memory game by getting correctly entering a sequence of twenty characters, the next game is a draw poker game.

The way it works is that you choose your bet (from 1 to 10) by pressing '2' to increment the bet and '5' to decrement the bet. Then, press 'F' to deal the five cards. The face value of the cards is displayed, and the suits can be seen at any time by holding down the PTT key. Any number of cards may be discarded, and to select (or deselect) a card for discarding, press the keys '1', '2', '3', '4', or '5'. If a card is selected for discard, it is displayed "face-down".

Press 'F' again to draw new cards. Your new cards will be displayed, and then if your hand is 2-pair or better, the screen will show the rank of your hand on the left (2P for 2-pair, 4K for four-of-a-kind, etc.). On the right the pay-off for that hand will be displayed. Your bet is multiplied by the pay-off factor,and the resulting pile of cash is displayed in the right hand side of the upper screen. (The left-hand side of the upper screen contains your table stakes, which are initially 100 coins from winning the Simon game.)

If you win the poker hand, pressing any key steps into the next stage. If you lose the poker hand, your bet is deducted from your stakes and you are asked to start another poker hand. In the next stage, you are asked "TRYB/S" which means, "Do you want to try double-or-nothing in a guessing game for Big or Small cards?" Press 'F' for yes, press TONE for no. If you say no, your winnings are credited into your stakes and you are asked to start another poker hand. If you say yes, then a single shuffling/incrementing card is displayed on the left, and three stars are displayed on the right. You have to choose to go for either BIG or SMALL, by pressing '2' or '5'. You can keep pressing '2' and '5' to change your mind. When you are ready, you must try to hit the 'F' key to stop the rotating card display, and the card will show, and you will either win, lose, or draw. If you draw, you have to play big/small again, I think. If you lose, your winnings are gone and you can play poker again. If you win, your winnings double and you are asked whether you want to play big/small again.

The payoffs on the poker are set against you, odds-wise; the double-or-nothing game includes a draw, so the odds are against the player there unless you can time hitting the 'F' key to win more than half the rounds. I haven't managed to do this, so I don't know if there is anything beyond this, all I know is that when the table stakes are exhausted, you go back to playing Simon again.
TH-78 - antenna hints

Hello everybody! Recently I decided to check the performances of small "Duckie" antenna specified as T90-0444-XX in TH78 manual.
I found that on 2 mtrs band this antenna, at first, has quite narrow bandwidth and, at second, tuned about 144.000 MHz or even some lower ( at the same time 70cm bandwidth seems to be enough...).
Because of "integrated design" of this antenna it would be nonsence to cut the top end, so I tried to find another way to tune it to the middle of 2m band. At last, the problem has been successfully solved! So, you can easy tune the central frequency up to 147 MHz - just place a copper ring in the middle of conical surface of antenna ( between "OO"s as shown below ):

  +---------------¾---

  |--  |          |     +-----------------------------+

  |--  | K E N W O|O D   | dual band antenna           |)

  |--  |          |     /+-----------------------------+

  +------------------/

               copper ring (about 13 mm internal diameter)

The ring made of 0.3 mm wire gave me frequency shift from 144 to 145 MHz; if you need higher frequency, you should use wider ring ( about 4...5 mm for 147 MHz ) - you can solder it of thin copper.
Don't use SWR meter for tuning! The best device is scanning scope or, at least, simplest RF field meter and your HT as VHF generator.

TH-78A (U.S.A. version) --> TH78E (European version) MODS.

If you bought a TH78A in the USA you don't have the 1750 Hz repeater tone access, but you can change that !

Apart from the well-known six diodes, the new CPU has 2 green wires.

In order to use the TH78A in EU, you must do the following:

First you have to remove D2 for the standard EU bands (144-146 and 430-440 MHz).
Now control that the 2 green wires and the 5 other diodes are installed (D1, D3, D4, D5 and D6).
If you need band expantion and components location, please see the mods below.

Although the TH78A has a special bandpass filter for the US 70cm band, I could not notice a decrease in sensitivity in the EU part of the 70 cm band.

There is a function change for 3 knobs; please see below and also p. 6 and 7 of your INSTRUCTION MANUAL.

    TH-78A   -->   TH-78E

    ---------------------------

    LAMP     -->   TONE 1750 Hz

    CALL     -->   LAMP

    TONE     -->   CALL

Now, you can choice between the CTCSS tones and the 1750 Hz with the following sequence: F + LAMP (the new TONE !) and then the right rotary encoder to make your frequency choice.
Crossband repeat, extended RX/TX

Owner assumes all responsibility for modifying or using these modifications!.

The following mods will provide for Crossband Repeat and extended receive and transmit on the Kenwood TH-78A HT.

I believe other functions are also enabled by these mods. which I have not found yet but I will update the file as news progresses.

Diode #4- Crossband Repeat
Diode #5- Extended Receive and out of band Transmit.

Remove all screws and open radio as explained in the Kenwood manual for installing the memory expansion module.
On the back cover you will find the memory expansion module socket and a copper shield to the upper left corner of it.
Under this shield their will be a row of SMC diodes which are unmarked in a vertical configuration to the lower right portion covered by the shield.

Remove the shield at its four corners with a solder sucker and SMALL! iron.
Carefully count down from the 1st diode in the row to the fourth one and remove for crossband repeat.
HINT: I found if you BRIEFLY touch the iron to the right side lead while gently pulling up on the SMC diode it should completely come off without needing to apply heat to the other side and further risk board damage.
I used a pair of right angle surgical tweezers for this.
Just as above you may remove the fifth diode to preform the extended receive and transmit modification.
Reset the CPU (yes you will loose all of your programed memories! argh!) by pressing Function for more than one second and then "0".
YOU HAVE NOW COMPLETED THE MODIFICATIONS!
For 800Mhz go to the UHF band with the band switch and press Function for more than one second quickly following with a press of the Band switch again. 8---.-- will appear.
For 300MHz go to the VHF band and repeat as above. Original bands are restored by repeating the "F Band" sequence.

MY observations... All original functions have maintained the same which is great. Aircraft band which was accessible before the mod remains with the same characteristics. It seems that VHF-High band has improved a bit on sensivity where it was dead as a dog before the mod (above 155.000MHz) but the 162.000 MHz band where weather radio is is still a bit deaf for reception at any distance but about 20 Miles. This depends on your (or my) terrain and transmitter output power.

On UHF all public safety frequencies up to about 500 MHz seem to come in well but sensivity greatly drops from there (we really can't ask for more). Frequencies can be programed in up to the 920MHz ham band but I have no way of measuring sensivity. 800MHz works but the signals are very weak, you must be near the transmitter for reception. Assuming you are in the town or city where the transmissions originate it should work.

Transmit is enabled up to and incl. 500MHz but after testing this on a frequency counter I find that a signal is only generated to about 490 MHz, even though the trans. LED shows output in the higher frequencies.

Crossband repeat seems to work fine but the audio is unacceptable for use, BE AWARE the radio gets HOT! Prolonged use or use on a busy frequency would not be recommended. Also remember this is a dual band HT please use a proper antenna while in this mode to avoid a high SWR, we should all know better... Right?

After first booting up the CPU in the mod I found that the message screen showed "Cloning" so it seems that this radio now has cloning capabilities. After searching I have found that holding the "0" key and powering up the radio will display the clone feature, see below for further explination.This leads me to believe that this HT may have some more "Hidden" features that I am trying to find, some may be useful.

Thanks to Gary KC8UD who sent me the following via packet .....

CLONING:
The TH-78 can be cloned without cloning cables or special equipment. It is done entirely with RF, and, in fact, can be transmitted over the air, and even via repeaters. This may be extremely useful for those users who do not have the patience to program their own radios themselves. This application would also be useful for clubs and user groups. (However, this can take as long as 50 minutes with the ME-1 expansion module. It is recommended that a dummy load be used to prevent unwanted QRM.)

Both radios must be on the same frequency.
Activate both radios by pressing the "0" key while turning the power on. The radios will display CLONE.
Now, click the PTT of the "master" radio. The radio will transmit in the conomy low power mode. This may take about 4 minutes for fifty channels.
hen the data has been transferred, both radios will revert back to the riginal frequency.
Turn both radios off and then on again. They will now operate normaly while the slave radio has the same memory contents as the master radio.

FREQUENCY EXPANSION

(1) You can receive from 340 - 399.987 Mhz FM by removing chip diode D8 on the ontrol unit. To access this function, press the [F] key for one second, and then the [LOW] key. This toggles between AMATEUR, AIR band (AM) and 360 Mhz.
AM and FM modes are selected automatically, depending on frequency.

** Since "F" for a second and "Low" toggles the power output, I wonder **

There is also a couple of arcade type games on the TH-78A. To start the game you pres and hold [PTT] and [M] keys while turning the unit on. The first game is a follow me type game. The radio beeps and shows a sequence of numbers flashing on the screen. You have to match the same sequence on the tone pad. Each time the sequence gets longer by one number. You have to keep remembering the sequence as one gets added each time. Once you get to a certain high score on that game, it breaks into a poker type game. To exit the game mode press the LAMP key at any time. The receiver still works in the game mode and you can adjust volume but no other features.

RG> The games seem to work fine and it is interesting that they have inserted that into the programing of the chips. Does anyone know of any further features in the radio be it games or radio functions.

PLL With HEP4059

2009-11-16T08:52:00.000+07:00

7 Mc Spektrum JF1OZL

2009-11-11T09:01:00.000+07:00

7MHz band monitor scope
I made a 7MHz band monitor scope. It exchanges all existing signals of that timing of 7MHz-band to viewer image like a hill on the oscilloscope . See fig5! It indicates what it makes. You know it in the catalog of IC780. ** See fig1! it indicates block diagram. See fig2! It indicates circuit. Saw signal-oscillator makes 11Hz saw signal. This signal controls VCO. VCO oscillates a signal changing from 17.6MHz to 17.7MHz ,repeating 11 times in one second. DBM changes 7MHz signal came from antenna to 10.6MHz IF-signal by mixing the 7MHz signal with 17.6MHz changing frequency local oscillated signal. Yes. This is basically same with normal single super heterodyne radio. But, instead of audio AMP, detected signal is inserted to vertical arc of oscilloscope. Saw signal is injected to a horizontal arc of oscillator. See fig4. It indicates that too fast sweeper make filter dull. This circuit is a type of spectrum analyzer. But vertical hight do not indicate logarithmic strength (dbV) but linear(V). I joint a dipole to this machine. This machine displays a view like fig3. I can know the opening frequency of 7MHz band. I can know where is jaming. I can enjoy to see this view.

3.5 Mc One Transistor FET Transceiver

2009-11-11T08:53:00.000+07:00

VHF 30 W PA

2009-11-08T20:15:00.001+07:00

HF 600 W Power PA

2009-11-08T20:09:00.000+07:00

50 Mc FM Transceiver

2009-11-07T16:11:00.000+07:00

VFO

2009-11-07T16:07:00.000+07:00

100MHz Spectrum Analyzer

2009-11-03T06:37:00.000+07:00

100MHz Spectrum Analyzer

Iulian Rosu, VA3IUL / YO3DAC

http://www.qsl.net/va3iul/

This Spectrum Analyzer supposes to be a cheap and a useful device for any ham radio. To build this device you need minimum test equipment, like a digital counter, an oscilloscope, Grid-meter and a multi-meter. The main design is based on SA605D, FM receiver from Philips. This circuit is very common in some old analog cell phones.
If we take a look to the main schematic, we can see that the input signal pass through a low-pass filter (L1, C2, C3), and it is amplified by a MMIC, MAR6, in order to boost the weak signal performance of the instrument.
It is important to remember never to exceed the maximum input level specification of the Spectrum Analyzer. Do not confuse the maximum input level specification with the 1dB-compression point or third-order intercept point specification. The maximum input level specification is the maximum input level that will not damage the amplifier or mixer. The 1dB compression point or third-order intercept point refers to distortion caused by excessive input levels. The third-order intercept point usually occurs about 10dB-15dB above the 1dB-compression point. If an analyzer specifies the 1dB-compression point as 0dBm, then input levels higher than 0dBm should not be present at the output of the RF attenuator. If the RF attenuation is set for 20dB, then the input level (at the input connector) may be as high as +20dBm without exceeding the 1dB-compression point. It is always best to allow an extra few decibels of safety margin. For example, if the 1dB-compression point is 0dBm, then the input level should be kept several decibels below this point for best performance.
If we check Minicircuits catalogue we can find that the 1 dB compression point for MAR6 is 2dBm with a gain of 20dB at 100MHz. But in the same time the SBL-1 mixer support on its RF input signals only up to 9dBm. So in our case, the limit of input signals will be around –10dBm, to keep a good linearity of our measurements.
The range of the VCO, used to down convert the signal to first IF, is from 150MHz to 250MHz. The VCO can use any NPN RF transistor, like BFY90, BFR90 etc. The varicap diode should be MV209 or an equivalent diode, which can give a good, voltage versus capacity linearity. L9 from the tank circuit has 3 turns, on 3mm diameter and 5mm length. With a frequency counter connected to pin 8 of SBL-1 you can measure and adjust the frequency range of the VCO.
On the output of the SBL-1 mixer, we have the first IF filter on 150MHz. The bandwidth of this filter is 1MHz. Each inductor of the filter has 5 turns, 1mm silver plated wire, on 8mm diameter and 10mm length. The trimmer capacitors (2-12pF) are used to tune the filter. Another MAR6 is used to amplify the first IF signal.
The circuit SA605D is a high performance monolithic FM system incorporating a mixer/oscillator, two limiting amplifiers, quadrature detector, logarithmic received signal strength indicator (RSSI).
The input match of SA605D is C9, C10 and L7. The tank circuit of the 139.3MHz LO (used to down convert the signal to second IF) is C12, C13, C15, L8. L8 has 6 turns, on 4mm diameter. Check for the right LO frequency on pin nr 4. For a better frequency stability you can use a 139.3MHz crystal oscillator. The second IF is 10.7MHz. I chose this frequency because here we can find plenty of IF filters. The main schematic use only one X-tal filter, which will give to the analyzer a 15kHz RBW (resolution bandwidth). Its possible to use here switched filters, for different RBW. For 3kHz RBW, is possible to use a SSB filter and for 150kHz RBW, ceramic filters used in broadcast FM radios.
One of the most important part of SA605D is the RSSI indicator, that will be our logarithmic detector. You can see the RSSI vs Input level graph in SA605D Datasheet and SA605D Application Note.
TL084(d), in a log amplifier configuration drive the Y input of the oscilloscope. The other 3 amps of TL084 (a, b, c) are used to generate the sweep signal. The output of (b) it will drive the X input of the oscilloscope.
This design expect to be a cheap Spectrum Analyzer, but in the same time with nice performances. For more improvements you can add a step attenuator, more poles to the front end low pass filter, switchable filters on 10.7MHz IF, a variable BW video amplifier for vertical output etc.

Iulian Rosu, VA3IUL / YO3DAC

Home http://www.qsl.net/va3iul/

Block Diagram

Low Noise VFO 5 Mc - 5.5 Mc

2009-11-03T06:32:00.000+07:00

Mizuho MX21S Schematic

2009-11-03T06:28:00.000+07:00

Generator 2 Mc - 12 mc

2009-11-02T06:41:00.000+07:00

VFO 7 Mc - 7.3 Mc

2009-11-02T06:38:00.000+07:00

VFO 5.5 Mc - 4 Mc

2009-11-02T06:22:00.000+07:00

Wee Willy Transceiver DSB 3.5 Mc

2009-10-30T17:37:00.000+07:00

VE7GC Wee Willy 75 Meter DSB Transceiver Project
Introduction
I meet a lot of interesting amateur radio enthusiasts online and on the air. Among them is Dick Pattinson, VE7GC who was first licensed in 1934. When Dick isn't sailing he builds and operates his homebrew QRP gear to hams around the west coast of Canada and the U.S.
Presented is a double sideband transceiver that Dick calls "Wee Willy". This rig has a low parts count and is easily built using non-etched PC board techniques. Dick even makes his own radio case using copper clad PC board for the front and back panels and cardboard for the rest of the case. The set itself is in a case 1 1/4 by 2 1/4 by 5 1/2 inches. There is a separate container which holds a 6 volt rechargeable battery and speaker. The speaker/battery case is about 2 1/2 inches cubed and is not shown.
The circuits are built in three sections on the circuit board, namely TX, RX, and VFO. An electret condenser microphone is on front panel along with T/R switch, volume and frequency adjust. The back panel has the antenna jack, power input cord and the speaker jack. The battery pack has a 100 uF capacitor to across the power leads for additional filtering and is shown in the VFO schematic.
The text that follows is clipboard pastings from email that Dick sent me with some additional comments and expansions by me. Dick's project exemplifies practicality and innovation and with that is a major contribution for the QRPHB site.
________________________________________
Construction Methods
Dick's electronic construction method is quite fascinating and represents yet another derivation of ugly construction. The electronic wiring is done on single sided PC board, copper side up. Small holes are drilled through the PC board material to allow component leads to pass through them. Then the holes carrying active leads are chamfered ( countersunk ) with a larger drill bit which is not run all the way through the PC board. This leaves an ground-insulated side to the hole and prevents a component lead short circuit. The copper being topside allows both convenient and short component grounding. The Wee Willy parts layout is extremely neat and compact. Dick, presumably through practice has great skill with this technique and I plan to try it in the future.
The project case is constructed from 1/16th inch cardboard which is cut and bent to fit the electronic PC board. Once cut, the outer surface and edges at the front are covered with tissue paper or Kleenex (tm) type tissues soaked in white glue. The applied tissue paper and glue is allowed to dry and then additional coats are added to build up a body. Alternately, the cardboard case can be coated with lots of glue and the covering material imbedded in the glue. The air bubbles are pressed out and extra glue is added where necessary. When enough material has been added to cover up and strengthen the case joints and the glue is perfectly dry, the case is painted with Rust Coat Enamel available at hardware stores. The end result is a glossy, durable finish which looks very sharp.
________________________________________
Transmitter
This transmitter uses an electret condenser microphone ( Dick used an Archer 270-90 ). The mic is built right into the front panel of the chassis and this of course guarantees short mic leads. A 741 op amp is used as a speech amplifier which in turn drives the balanced modulator a Signetics NE602 doubly balanced mixer. The input and output impedance of the NE602 mixer is around 1500 ohms.
To adjust the transmitter, set the bias control on the VN10 stage to ground and tweak L1 to resonance using an RF probe or scope on the VN10 input. The input signal must be audio, spoken into the front panel microphone to get the DSB. Once L1 is tuned, connect a 50 ohm load to the antenna with some sort of RF indicator (such as a RF power meter) and advance the bias control to give a watt or so output. Then speaking into the microphone should result in a DSB signal suitable for communicating on QRP! No audio input should result in no RF output. The supplied voltage should be kept at 6 volts, remembering that NE602's cannot stand voltage greater than 9 volts. With suitable voltage control such as a 6.8 volt zener diode on these chips, one could use higher input voltage with a corresponding RF output.
There is another way of setting the bias on the VN10. After aligning L1, with a ammeter in the six volt supply line, advance the bias control until the input current increases about 10 mA (with no modulation). If you do not have an FT37-77 ferrite core, substitute 10 bifilar turns on a FT37-43 ferrite core for the T1 transformer

Receiver
The receiver is a direct conversion type with a manual RF gain control in the form of a 5K potentiometer. Listening to a weak signal on the desired frequency the RF stage and the mixer core ( T1 and T2 ) adjustments are made until you hear the loudest possible signal, keeping the input test signal as low as possible. When the receiver is connected to a doublet antenna there is no lack of incoming signal, which can be controlled by the front panel RF gain control.
The antenna and 6 volt supply is switched manually from TX to RX mode and back by a front panel mounted switch. If you can not find Tak Lee green 10.7 MHz IF coils, probably any other brand of 10.7 MHz slug tuned IF transformer would work. The Mouser catalog number 421F123 would work well and in another 80 meter project I used it with a 470 pF capacitor instead of the 330 pF cap shown. I would start with Dick's 330 pf cap and if it will not tune to resonance sharply, slightly increase the cap value up to see if a bit more capacity is required to resonate it on the desired 75 Meter frequency. Note that the secondary coil on the L1 transformer in the transmitter schematic is unused. If your 10.7 MHz IF coil has a built in capacitor at the base, remove it.
During receive, the standby drain current at 6.0 volts was 24 mA and on loud signals it rose to 100 mA. If this is too much, probably the easiest thing to do would be to put in a series resistor from positive to the LM386 to limit the drain current. To get output on the speaker it is a matter of how loud you want it for the drain you draw. If earphone only reception is okay, then the drain could be reduced considerably.

VFO
Dick's diagram indicate that this VFO was based upon a design presented in SPRAT for summer 1995. The main inductor L1 is wound with #32 AWG wire on a 1/4 inch slug-tuned coil former. This coil would have an XL somewhere between 250 - 310 ohms, so if you cannot find a coil former as described , you could easily wind one on a powdered iron toroid and make a portion of the C1 capacity variable for adjustment. A suggested alternate inductor is 53 turns of #26 AWG on a T68-6 core powdered iron core.
Dick suggests checking an old television to find suitable coil formers such as the one he used. It would probably be best to distribute the 120 pF C1 capacity among 3-4 capacitors to enhance stability. These caps should be NP0 ceramic for best results with frequency stability.
Dick's oscillator uses the slug tuned core to put VFO frequency close in frequency to where you want to operate and the variable resistor tuner on the front panel allows adjustment around the incoming signal to get the correct pitch. The desired band-edge is easily set by adjusting the slug while listening to the VFO frequency as audio on another receiver that has a frequency readout or directly with a frequency counter.
The L2 150 uH RF choke can be a simple epoxy unit which resembles a resistor. The D1 variable capacitance diode is a BB104 which has ~ 35 pF capacitance on each side. These are available at Dan's Small Parts and Kits whose URL is in the Links section of the site info web page. Experimentation with other tuning diodes could produce a practical alternative to the specified D1 part.

________________________________________
Operating Wee Willy
Dick sent me Willy in the mail and the first available moment I fired the little rig up and spanned the VFO which tuned from ~ 3721 to 3738 KHz. I then proceeded to tune 3729, the frequency of BCEN, our SSB provincial public service net and on my first break was able to check in with one call sign repeat to the net control station. The band conditions were noisy and most signals were S8 or lower, however Wee Willy's 1.5 watts P.E.P. were able to check me in with my folded Marconi antenna. I later changed the L1 slug and worked some stations higher up the band. My audio reports were favorible and no one knew I was running DSB. This is a fun radio and it looks cute to boot!
When transmitting, I had to be careful to keep my hand away from the VFO compartment to prevent pulling the VFO frequency with the capacitance change from my hand. The VFO has reasonable long term frequency stability and copying CW stations with the receiver was possible without frequent tuning readjustments.
The following are some digital photos of Wee Willy taken by VE7ZAC.
Move your mouse over the images for a larger version.

Capacitance Meter using DVM

2009-10-30T17:34:00.000+07:00

FM Super Mini Transmiter

2009-10-29T08:41:00.000+07:00

Satelite Finder

2009-10-27T14:07:00.000+07:00

144 Mc SSB Receiver

2009-10-27T14:01:00.000+07:00

100 W Linear Amplifier 144 Mc

2009-10-27T13:58:00.000+07:00

40 W Linear Amplifier 88 Mc - 108 Mc

2009-10-27T13:55:00.000+07:00

Simple TV Modulator

2009-10-26T06:38:00.000+07:00

Ultra Simple 3.5 Mc SSB Receiver

2009-10-26T06:32:00.001+07:00

7 Mc SSB Transceiver

2009-10-26T06:29:00.000+07:00

50 Mc DSB Transceiver

2009-10-26T06:26:00.000+07:00

TV Modulator (2)

2009-10-26T06:17:00.000+07:00

TV Modulator

2009-10-26T06:08:00.000+07:00

FM Receiver 144 Mc

2009-10-26T06:02:00.000+07:00

Low Noise Pre Amp (2) 144 Mc

2009-10-26T05:59:00.000+07:00

Low Noise Pre Amp 144 Mc

2009-10-26T05:56:00.000+07:00

VHF Beacon3

2009-10-26T05:53:00.000+07:00

VHF Beacon 2

2009-10-26T05:51:00.000+07:00

VHF Beacon

2009-10-23T09:14:00.000+07:00

2m Transceiver AM

2009-10-21T07:18:00.000+07:00

S Meter for Icom IC 2N

2009-10-20T16:00:00.000+07:00

Signal Meter for Icom IC 2N

Schema Icom IC 2A/ 2AT

2009-10-20T15:51:00.000+07:00

Modification extend Frequency Icom IC 2N

2009-10-20T07:28:00.000+07:00

MODification File For ICOM IC-2AT
---------------------------------
If you have studied the schematic diagram for this radio,
you will notice that pins 15 and 16 are not indicated on
the programmable divider chip IC1 (TC9122).
By simply connecting pin 15 thru a switch to pin 1, you will
be able to move the radio up in frequency by 10 MHZ.

Some of these radios were sold without covering 140-150 MHZ.
The modification for this extended coverage is described below:
1) Open up the radio and locate the FLEXIBLE BOARD, this connects
the thumbwheel switches to the MAIN BOARD.
2) At the MAIN BOARD end of the FLEXIBLE BOARD, add a jumper at
location C4. There should already be a jumper at location C2.
3) At the thumbwheel switch end of the FLEXIBLE BOARD, remove the
jumper which connects C3 and COM.
4) Reassemble the radio. Coverage is now 140-150 MHZ.(MARS/CAP)

Now, if you activate the switch described above, the radio will
now operate in the 150-160 MHZ range, after L3 adjustment,
described below.

OPERATION and L3 ADJUSTMENT:
----------------------------
1) Activate switch and dial up a known active frequency.
2) Adjust L3 until PLL locks up and radio begins receiving.
(you need an active frequency to tell when this happens)
3) To return to 140-150 MHZ, repeat above steps with switch off.

NOTES and DISCLAIMER
--------------------
1) Drill a hole in the case of the radio so that L3 can be
adjusted from outside of the radio.
2) The above information is presented for educational
purposes only, and is not an endorsement of any particular
practice.
3) This MOD has been in operation for 6 years with no ill
effects on the radio
4) This MOD courtesy N2MOD.
--------------------------------------------------------------------------
Note: I haven't tried or verified this, proceed at your own risk. And
do not transmit outside of legal bands!

Manual TRA 921

2009-10-12T08:57:00.000+07:00

Forsale Manual Racal TRA 921
Email : radiobekas@gmail.com

Collins Filter

2009-10-06T06:32:00.000+07:00

For sale 2 Collins Filter with filter specification :
Filter Spek 1: 500 B 60, 9R2, 526900900
Filter Spek 2: 500 B 31, 8R2, 526900800

Email : radiobekas@gmail.com

Radio Bekas

2009-09-08T10:52:00.000+07:00

Radio Bekas.blogspot.com.
More information amateur radio transceiver, antenna, power supply, linear amplifier, etc.

http://radio-bekas.blogspot.com