Power amplifier

Power amplifiers usually cause the most problems, this one is no exception.

I retrieved some cores from a PC power supply. They seem to work. For the time being the amplifier uses 2 IRF510 mosfets. I will switch to more powerful types later. The amplifier should work in class D.  The amplifier puts out 30 Watts but efficiency is low 60%.

The problem seems to be the mosfet drivers. I tried to drive them directly from TTL at 6 Volts. It did work but efficiency was 40% or less. Then I tried 2 driving transistors. That improved the efficiency  but it is still not good enough. I will try TC4427 drivers.

500 KHz bandpass filter and preamp

I made a bandfilter for 500 KHz. I have also added a preamp as it turned out the filter has 6 db attenuation.
The preamp has to compensate for the loss. It also has to compensate for the loss in the mixer.
It seems to work fine but I have to test the noise behavior. Gain is 6db, the -6db band width is 10 KHz.

I have several 455 KHz If transformers. They can be tuned to 500 KHz easily. However matching to 50 Ohm is difficult. I also tried filters using FT50-43 cores but that was a bad idea. The -6db bandwidth was 100 KHz.  Matching to 50 Ohm was OK though. So I use one FT50-43 filter to match the impedance of the IF transformers.

Alternatively I could have used air coils. Then the filter would be bulky.

The transistor get a bit hot I will keep an eye on it. I may have to use a heat sink. 

status 500 KHz project

This is the current state of the project. TX works for CW . Reception works but bandfilter for RX won't fit in this tin box. Next step is to add the AGC amplifier.