[AMPS] exciter to amp coax length

[Pete Smith]

>From time to time, people have mentioned how Collins used to recommend a
certain length of coax between the KWM2 and 30L1 amplifier.  As the
following anecdote may illustrate, this isn't just ancient history.  I hope
this story helps someone else troubleshoot a similar problem. 

Recently, I redid the T/R relay system in my SB-220 to add QSK, and was
perplexed to discover, after the modification, that the amplifier suddenly
showed a high input SWR on 40m (only), as well as abnormally high gain,
grid current and plate current on that band only.  Visions of an HF
oscillation, or some other abnormality, had me digging for answers.  

Thanks to Tom, W8JI, who asked if I had changed anything else at the same
time.  Eureka!  I had "improved" the jumper from exciter to amplifier by
shortening it about 8 feet.  Just now, I put the old one back in, and
everything is back to normal.  I don't pretend to understand WHY this
happens, or why it happens only on one band, but there you have it.



73, Pete Smith N4ZR
n4zr@contesting.com 

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