Posted by
Don Wilhelm-4 on
Oct 14, 2007; 10:08pm
URL: http://elecraft.85.s1.nabble.com/K2-Is-TX-frequency-susceptible-to-RF-on-chassis-tp454716p454717.html
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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