I have similar observations on the ANC4 espc on 160 and the need for both a
large sense antenna and a way of controlling main antenna gain.
I use a step attenuator on my main rcvr line to adjust the main ant sig level
which works fairly well on 160. W2JPW who has a specific problem with one
point source of noise uses a small magnetic loop aimed at the noise for the
sense antenna and that works well for him.
I have also added a small transmatch on the noise port which allows me to tune
(or detune) the sense antenna and this works very well - esp reducing IMD
problems but adds complexity to the operation.
73 Pete
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