[Elecraft] Nulling QRM

[AD6XY]

Thanks for the interesting reply Lyle,

I am mostly interested in operating on HF. QRM is not such an issue on HF as
the signal to noise is so much worse. I know what you mean about minimizing
the gain before the selectivity but at VHF one has a low noise floor to work
with so that does not really work. You need a low MDS.

I operate with the XV144 and with the pre-amp off and with a 15 dB
attenuator in the 28MHz IF. This does nothing good for the noise figure of
course but I have a switchable pre-amp at the front to deal with that if
needed. The XV144 has a bit too much gain for my situation and I am looking
forward to the internal 144MHz option arriving on my doorstep next month.

I don't think the limit is the hardware AGC - I thought it was the DSP one
responding to the very high signal energy within the filter bandwidth but
outside the main passband. I agree a tighter filter would help. I would like
a variable crystal filter please! I am prepared to build my own if the K3
can be made to tune it.

The K3 deals with this situation very much better than anything else,
especially now I have fixed the VCO spurii problem. It is a monthly
inter-club sprint contest and I have 2 other stations within a mile and line
of sight.

In the interim, I am thinking of perhaps using a second antenna and seeing
if I can do this nulling at RF. 

Mike
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