Almost ready

The transverter is almost ready. I could add the bias current temperature stabilizer.
I might do that in the future. It may be good enough though. I have reduce the power to 5 Watt so it is not getting that hot anymore. Five watt is enough to drive my lineair amplifier.

I tried to make contacts using it bare bones. So far I have not had any luck. It should be possible though. I have a lineair amplifier that can provide 200 watt PEP using 5-10 watt drive. I will use that amplifier to boost the signal. It should make things easier. In the future I may build a PA for the lower bands using IRF510 fets.

I will try to make a movie clip showing its receive capabilities.

New output transformer

I made a new output transformer for the PA. I used less turns and more ferrite.So I was able to use wire with a larger diameter.It worked out fine. I can get a bit more than 10 Watt output, measured after the low pass filter. Input current was 1,8 Ampere. This result is OK.

The transformer has 2*2 turns primary and 9 turns secondary. SM0VPO uses 3*3 turns primay and 16 secondary.My transformer is made by 3 2 hole ferrite cores. Brand is unknown. This is the third transformer I tried. My maximum power is limited to 12 Watt theoretically. That is OK I will use the PA at 7-8 Watts maximum. The SSB signal sounds good on my receiver. I didn't notice splatter on nearby frequencies.

I really have to implement temperature compensation. Now It suffers from thermal runaway (DC bias current increases when temperatere rises). For SSB speach it is not a problem. It is a problem when a carrier at full power is being transmitted (AM mode). AM is not needed ,I (mis)use it for tuning the antenna though.

Low pass filter and fan regulator

I just built the Lowpass filter using info from the ARRL handbook. I have used the 5 pole Chebychev filter. That sould be enough. It seems to work although I can not measure its characteristics yet. The output signal is not attenuated much. the output looks clean on a 100 MHz scope. I have to wait until my spectrum analyser project has finished. Than I can be sure.

The PA does not have enough cooling, so I added a fan. The fan starts when a transmission starts. After the transmission stops, it stays on for a few secons. I made a circuit to accomplish that.

After pushing the PTT switch I hear a tjoep signal on my SW receiver. I will have to find out why that happens. It is a bit anoying.

I found a similar power amplifier in a previous project. That PA has a better output transformer. It puts out 5 watts too but the efficiency is much better. I 'll rebuild the transformer using the same ferrite core type.Then I may get out a bit more power. That would be nice.

amplifier news

This picture shows the amplifier.

It is not 100% the same as the SM0VPO amplifier.
I did not use a thermistor in the the bias current regulator. When I find a 1K thermistor I will add it. Now I just use a 1 K resistor. The bias circuit for the driver is different too. I don't remember why I changed that.

The amplifier works but I can only get 5 watt output. I add a few capacitor to smoothen the base and the collector voltages. They are sinus shaped now. Without those capacitors the signals cointains spikes.
A problem is that collector voltages reach their maximum at 7 Watt. That should not happen. I tried different ouput transformers but the results are the same. The output voltages divided by the input volatges just doesn't match the turn ratio. Input current of the finals is 1.5 Ampere for 5 watt output, so the efficiency is low too.

I will have to investigate what is wrong meanwhile I keep using amplifier as it is stable. I did not see it oscillate, even when SWR was high. The output looks clean.
Then I checked the audio. It souns good on a shortwave receiver.

Next task is to improve power and efficiency and build a lowpass filter.

Power amplifier.

Some time ago I tried to build a 10 watt amplifier for all HF bands. I found one designed by Harry lythal SMOVPO. See 10 watt hf amplifier It did work but I had problems making it work for all bands between 3 and 30 MHz. If I remember correctly it worked fine up to 10 MHz. It was unusable back then.It should be fine for 40 meter though. I will try to make this amplifier work again. The output transformer and the input transformer are missing so my next task is to build these transformers again.

Meanwhile I found a suitable enclosure for the transverter. On I flea marked I bough a automatic printer switch. It is obsolete but it is build in nice a solid metal box.That box makes an ideal enclosere for the transverter.