[Elecraft] K3/100 RF Feedback/Spurious oscillations ?

[Andrew Faber]

Stewart,
  I reported something similar after CQWW CW, and there was some discussion 
about isolation between the RX antenna input and the TX stages of the radio. 
I'm not sure if there is a plan to do anything about it or not, but would be 
interested in solving this problem, as it impacted my ability to use our 
beverages on RX.
  73, andy, ae6y, p49y
----- Original Message ----- 
From: "Stewart Baker" <stewart at baker.nildram.co.uk>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Thursday, January 31, 2008 8:14 AM
Subject: [Elecraft] K3/100 RF Feedback/Spurious oscillations ?


Very strange effect noticed today when tuning up on 20m.

At power levels above 20 w on 14.175 my external Palstar SWR meter
would suddenly leap from 1:1 to above 5:1. Also the K3 SWR display
showed similar. High current was also reported. No problems with
either a TS850S or K2, both OK up to 100W.

Switching the RX Ant switch to the main antenna or removing the RX
Antenna  BNC lead cured the problem.

I use the RX antenna input for 2 x Pennant loops for the LF bands,
but find that they sometimes give a better SNR than the main
antenna on higher bands. The main antenna system is a doublet fed
with open wire feeders into a fully balanced (no toroid on output)
ATU.

My initial thoughts is that there might be some spurious output
generated by an obscure feedback path from the RX antenna input.
If this output were on a frequency well separated from the desired
then it could show up as as high SWR.

What think Ye ?

73
Stewart G3RXQ
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