Dear All,
As there is some discussion on PA waveforms and matching, I thought it
might be useful to add the following input. Sunday morning before last
there was the usual hive of activity on 136, not a signal to be heard,
so I put my auto keyer on with the Tx running at the 800 watt level
while I went and got on with the gardening.
Part way thro a long, long CQ, the far end 200 ft fell off my 1100 ft
antenna, thus presenting a considerable mis-match to the transmitter.
When I returned to the shack, I observed that the antenna current had
dropped from the normal 4 amps to less than an amp. The PA appears to
have survived without damage.
The point about this is that the only protection my Tx has is an over
current limit, which had not tripped. There is no SWR protection.
The PA is a 'chinese' copy of the Decca 4 FET bridge circuit, but with a
'YXM/MRF' output circuit with LPF and tapped transformer instead of the
Decca series tuned circuit. I would recommend anyone to use this
arrangement because it seems to be bomb proof and I have yet to lose a
FET. I cannot say the same about the 2 X FET 'YXM/MRF' PA configuration
used previously. I still have the pile of dead FETs!
73, Tom G3OLB
p.s I still didn't get an answer to my CQ!
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