I mentioned yesterday that after retuning my vertical I had a
diabolical swr at the shack end. That turned out to be because the pa
was going unstable when it saw a 50 ohm load!!!
I have now done a few changes to the pa to hopefully get round this
problem. The T50-61 toroid I had used for the pa output coupling
transformer wasn't really up to the job and was getting hot. I have
replaced that with a 26mm 3C85 toroid from my 136 stock and
reconfigured it to be an isolating transformer which gets rid of a
nasty series coupling capacitor. I have also done a couple of changes
with the decoupling. My website has the updated circuit. It now seems
to be stable and also putting out a bit more umpth.
My antenna tuning exercise yesterday has certainly got it one
frequency (maybe a little on the low side as it is 50 ohm resistive
at 501kHz and rises to 67.8ohms slightly reactive at 504kHz).
Excellent SWR!
It obviously has worked as I have just had a (slightly scratchy) chat
with G3UNT followed by a nice QSO with Mike G3KZU in Oxford. Brian
has never heard me before!
73 Dave G3YMC
http://www.davesergeant.com
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