Re: Ultra VLF signals?
I recall noticing that one of the "SWL"-type ATUs that was on the market a couple of decades back (Mizuho/Global/MFJ?- that sort of thing) had a sub-500kHz switch that brought in a LPF, I assume that this was to suit the then current range of consumer/amateur type receivers that may have offered LF coverage, but didn't necessarily budget for front-end filtering/sufficiently butch front-end and mixer devices to give good results.
The Racal LF converter made to go with the RA17 makes for an interesting circuit browse, with its care over balancing and filtering.
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