80 /20 MHz transceiver fan problem audio problem

I have decided to make the transceiver for 80 meter only. I may reconsider but I don't want to spend too much time on this radio
I intend to use it as a signals source for experiments with IRF510 based amplifier for 80 meter.

The power amplifier need some cooling. I have some PC fans that should be usable. They work great but they introduce hum in the audio. It comes via the power supply. No problem was seen when the fan was powered from outside the enclosure. Even when using the same power supply. Getting the fan power from within the radio causes a big hum. Adding capacitors does not help. I don't understand this.

One of the problems with this radio is that the audio is low in volume. So I have added an additional preamp. It works audio is at an acceptable level. I would like a bit more but it is Ok for now.
Unfortunately

My 20Ampere power supply has a problem. Once in a while it is not 13.8 V as it should be but 18+ V instead. That power is then stable at 18V for a while. Unfortunately this broke the audio PA. Smoke can out of it,

80/20 mhz transceiver

I found out what the reason was for the bad carrier suppression at 20 meter. The problem is the sideband oscillator.  I did not have the xtal for usb. so I have use a 27 MHz  on its fundamental frequency of 9 MHz. I had to make provisions to tune it to the right frequency. That worked but the signal shape is not a nice sine wave. This causes bad suppression of the carrier.
I will make an separate sideband oscillator with some filtering. That should fix the problem.

I have made an enclosure for the radiomyself. Using some laminated wooden furniture plate and some PCB plates. A picture will follow soon.
A metal case would look better but I don't want to spend too much money on this radio . However it is retro style. That suits the radio fine.

I will make a separate box with a PLL synthesizer to improve the stability. The PLL is working. It was leftover from another project. I need to make a  controller for it using a microcontroller.

CHN 80-20 tranceiver continued

I fixed the problem with the RIT. It was wired incorrectly.

The TX/Rx leds now work for both 80 and 20 meter. These too were wired incorrectly.

Somehow I made shortcircuit somewhere. This blew a BD137 power transistor.
Fortunately I had a few more in the junk box.

At 80 meters I was able to get a bit more than 10 Watts CW. SSB however was at 3 Watt max.
I have checked all circuits. They seem ok. I fixed it by making a small mar 4 based amplifier. Now I get 10 Watt PEP out. Current is 3 Ampere at 13.8 Volt

On 20 meter it does not work that well. Output is 3 Watt PEP. The input signal is according to spec.
Looking at the signal levels in the PA module it seems that I cannot input more signal.
More signal will cause an distorted output signal. It should be possible to get 10 watts at 20 meter though. I have another power module without transistors. I will try 27 MHZ transistors instead of the BD137. I hope that does the trick.

One of the remaining problems is the enclosure. I need to make a cover for the top left right and the bottom. I hope I can get some aluminum cheap.



 

a new toy

I have a new toy. A HP spectrum analyzer that works up to 350 MHz.

I already own a spectrum analyzer. It is an Atten that works from 0 to 1000MHz. It only has 1 filter that is  more than 200 KHz wide. It is usable but this HP is much better.

TR7200

Two years ago I bought a Kenwood TR7200. It is a well know 2 meter FM radio. It uses xtals

 I did not use it much as I only have 2 channels that are usable.
The other xtals were for USA frequencies  in the 146 MHz range.

Now I bought some xtals for it. Now I can use the following frequencies.

• 145.500
• 145.550
• 145.400
• 145.350

I also have a set for 145.325. Unfortunately the TX xtal works on 145,300. Although 145.325 is written on it. I can adjust the frequency a bit using the trimmers in the set. However 25 KHz is too much.

CHN transceiver update

I did some rpairs on the CHN transceiver.

• -X/RX relais was wired incorrectly. Fixed that
• It contains a variable capacitor at the front. It is used to peak output for the 80 meter band.This capacitor was not working correctly. Fortunately I had a similar capacitor in the junkbox box.That one worked OK.
• The IF board needed alignment. Fixed that.
• Improved decoupling of PA board.

HF PA's usually causes head ages. This one is no exception.
I can get 14 watts CW on 80 meters. On 20 meter it was just 4-5 watts. SSB PEP is lower.
at 80 meter I can get 6 watt. on 20 meter it is about 2 Watt max.
In CW mode the signal does not go through the xtal filter. It is much stronger than the SSB signal.
So I need to get some more gain of the ssb signal.

The PA suffered from some strange distortion. At full power It works for 1 second. then the sinus starts to deteriorate. It does not seem to be oscillation. After a small pause I can get another second with a clean signal.
I tried to solve  it using forced cooling. It helped but it is was not enough.

The power transistors  6xBD137 were mounted on a small heatsink. No cooling paste was used.
I think this causes the problem. A hotspot temperature is getting to high. That may be the reason for the deteriorated signal. So I applied some paste.
I also mounted two 10 Ohm resistors in series over the input transformer of the PA.
This reduces the power to 7-8 Watt but the signal is clean. It looked OK even when the dummyload was removed. Usually PA's start to oscillate when I try this.
I don't need a lot of power though. I need only a few watts as input for a bigger amplifier. So I won';t try to getr max power out of it

Things to do.

• Get more gain for SSB.
• Carrier is not suppression is not good om 20 meter. It is quite allright on 80 meter though.
• RIT works but I can not tune  to the same frequency I had when RIT is off.
• Find an enclosure for the set.

chn-8020 transceiver

I just bought a defect chn-8020 transceiver from a fellow ham.

The transceiver is a home made transceiver designed in 1980 ? by PA0CHN It covers 2 bands, 20 meter and 80 meters. ssb/cw 10W output. IF is 9 MHz.'
It iused to be popular here in the netherlands.

This  unit was not in a good state. It needs a lot of work. It was not completed by the builder.
It was not build by the ham I bought it from so its history was unclear.
Some components were missing and some wiring was missing or just incorrect.
Fortunately the difficult components were mounted including the 9MHz xtal filter.

When I fired it up it did not do much. A light was working and i heared some cracking noise from the speaker while turning the volume knob.

I found that the VFO did work. The audio module worked a bit after cleaning the contacts.
The audio module also contains the sidband xtal scillators and a mixer. So I applied a very strong 9 MHz signal on the input. I could hear it weakly from the speaker. So it has some life in it