"I find a low pass filter on the speaker line cures any receiver's high
frequency bleed through. There was one published in QST a year or two
ago. Mine uses a 70 volt to voice transformer to raise the impedance.
Actually I switch the impedance and capacitances to get different cut
off frequencies with the same inductors. Then have a second transformer
to get back to speaker impedance. With no active devices in the filter
(7th order cheybychev low pass) there is no detectable noise added by
the filter."
Same here, but designed a passive headphones bandpass filter mainly for
CW. It rids hi-fi cans of hiss and thumps; also sounds excellent on SSB.
It is an L-C filter based on a Z of about 200 ohms, since that is a
cross between the series resistors used at the headphones jack, and the
400 or so ohms of most of my cans. Dead silence from hiss; clean
sidetone--built from junk box. Only critical part: it must be assembled
into ROI-TAN cigar box for proper 'tone'.
73, Roy K6XK
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