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.
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