BITX20 Update #18

This morning I added a switch and socket so I could substitute my external DDS for the internal VFO. This gives me the functionality of knowing exactly where I am transmitting and receiving.

I need to change the inductor and capacitors in the VFO section to get some stability as well.

I also tried the BITX20 on a couple of antennas and found my first major problem.

When I put the BITX20V3 on my inverted Vee I get oscillation of around 1 watt that goes away when I touch Q1 2N2218 with my finger.

When I put the BITX20V3 on my 20m ground plane I get the similar oscillation but it doesn’t go away when I touch Q1 2N2218 with my finger.

I am not sure what is causing this and it will be interesting to find out. I measured the frequency of the oscillation using the CRO and it seems to be between 14 and 16 MHz. I will put the frequency counter on it next time I am in the shack and get the real answer. A quick tune around with the FT757 showed a number of signals at very high level inside the 20m band.

I need to get on top of this problem so I can use a variety of antennas when I go portable.

I have posted a message to the BITX20 yahoo forum seeking advice so it will be good to get other’s opinions on my problem.

I also need to re-work the transformers in and out of the IRF510 in the linear amplifier to get the pass band around 14 MHz rather than 10 MHz as it is at present. I’m hoping that if I take one or two turns off the transformer it will all come good.


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