The usual practice would be to have the preamp right next to
the loop and the coax between preamp and soundcard, with an
isolating transformer to help keep interference at bay.

With an unbalanced unshielded loop, I think the isolating
transformer will be quite important here.

Alpha looks like a good signal which is promising.

> However, since the 50Hz harmonics mainly produce narrow-band
> spectral lines in the waterfall, these should not be a great
> problem for receiving very narrow band QRSS-type modes,
> providing the frequencies do not coincide exactly.

The mains harmonics often have a rich spectrum of sidebands,
especially in the H-field, so you may still experience problems.

There are two ways for interference to couple into the rx -
direct pickup by the loop, and coupling from the domestic
ground along the feeder to earth via the loop's external
capacitance. The isolating transformer greatly reduces this
second source but there's not much you can do about the first
other than siting the loop as far away from house and powerlines
as possible.

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Paul Nicholson
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