Posted by
David Woolley (E.L) on
Oct 14, 2007; 7:30pm
URL: http://elecraft.85.s1.nabble.com/K2-Is-TX-frequency-susceptible-to-RF-on-chassis-tp454716.html
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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