Working, more or less

It has been a long time after the last entry. Building was going on though.
I was able to get the strength of the harmonics to acceptable values.
All modules are build on the breadboard. I did not want a enclosure because of the price. This radio won't be used a lot due to its limitations (power output frequency range)
I may reconsider this though.

Finally the transceiver worked on the dummy load. I got about 1 watt output. The signal sounded clean. Harmonics suppression was adequate. Then I connected it to the antenna. That caused a lot of problems. At first I thought The PA was oscillating but it wasn't. It turned out had severe RFI. I had to rearrange modules and wiring. Now it seems to be OK. To solve it once and for all I need to build it in a metal case.

I think I will try to find a cheap enclosure to build it in. I may add a S meter and a frequency counter.

1 watt amplifier

Finally I found some time to build the amplifier.
The goal was to get at least 1 Watt output without too much distortion.
I made a push pull amplifier using two 2n3866 transistors. The result was not good.
The maximum output power was 0.5 Watt with 30% efficiency. I blew a few transistors.

The 2n3866 was not a good choice as it is intended for 28 volts. So I got some 2n4427 transistors. Those worked better. I can get >1 watt output. harmonics are -20 dbc down. Efficiency is better than 40%.

At the moment I am building a lowpass fiter to suppress harmonics. Using a 3 element lowpass filter I was able to get 1,5 watt output. This filter also improves the matching. Harmonics are -35 dbc . I am replacing this filter with a 5 element filter to get the required suppression of the harmonics.

So far it seems that the 3th harmonic is still too strong at -40dbc. I may have to use better capacitors. The coils are aircoils so those should be OK.