[Elecraft] [K2] Is TX frequency susceptible to RF on chassis?

[David Woolley]

This may be correlated with the balun thread.

 From the same station, I got a report that I was off frequency on 15m 
SSB and a more quantitative one, of 120Hz low, for 10m.  This was during 
a local contest, so I couldn't do a lot of investigation on air, and I 
may not get many SSB opportunities on these bands in the near future.

I checked the transmit frequency relative to the receive one with a 
dummy load, at 10 watts, and there is no problem.  It's possible that 
this is simply a combination of my voice and the filter settings, but it 
could also be that RF on the chassis is upsetting the BFO and/or 
reference oscillator control voltages.  Is this a known issue?

The method I used to check with the dummy load isn't easily adapted to a 
live antenna, but as I've observed that the K2 has EMC problems with UHF 
transmitters, I tried holding a PMR446 transmitter close to various 
chassis seams and managed to upset the frequency by a small amount (beat 
frequency when SPOTted onto the 14MHz birdie), maybe no more than about 
10Hz.  This happened well after the point where the RF pickup was 
upsetting the received audio.

On 15m I was using the balun, but the actual antenna is approximately 
resonant (disconnecting either side gives a strong drop in received 
noise).  On 10m the antenna would be more like anti-resonant, so I would 
expect much more signal on the chassis.  Unfortunately I didn't have a 
quantative report for 15m.

If the frequency is shifting due to RF on the chassis, my next priority 
really is going to have to be sorting out a good internal antenna 
solution.  External antennas are out of the question for various 
reasons, that includes flag poles - I don't have exclusive access to 
anything at ground level!
-- 
David Woolley
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