David,
I do not believe that RF on the chassis could easily cause a frequency
shift, but then who knows because each situation like that is different.
I suggest that you first take a good look at your SSB FL1 filter for
both LSB and USB. If you have the curently normal SSB filter width of
2.4 kHz I recommend that you set up Spectrogram with markers at 300 and
2600 Hz, then adjust the BFO to center the passband between those
markers. If you have the older 2.1 kHz filter use 300 and 2300 kHz markers.
With the 2.4 kHz filter aligned that way, you should be able to use it
for both transmit and receive with good fidelity and frequency
tracking. If you have an extremely 'bassy' voice, then you may want to
set FL2 up as I have described and set FL1 for a passband about 50 Hz
lower (250 to 2550 Hz) and use FL2 for receive.
If you are using the K2 frequency indication to 'net' on a given
frequency, your dial calibration may be off a bit. To get it right,
refer to the K2 Dial Calibration article on my website
http://w3fpr.qrpradio.com for techniques to accurately set the 4 MHz
reference oscillator and the following steps to achieve good dial
calibration.
Once you have assured yourself that the SSB filters are correct, try it
again and see if there appears to be any difference.
73,
Don W3FPR
David Woolley wrote:
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!
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