The notch filter in the FT-1000D is tuned by applying the passband shift
principle to the last (100 kHz) IF. The tuning of notch filter circuit itself
is fixed, nominally at exactly 100 kHz. When the notch filter is turned off,
a switching diode bypasses it, but the notch frequency control still shifts
the IF passband. The bandpass filters should be broad enough that shifting
the passband with the notch filter out shouldn't make much difference. I
suspect what is happening in some of these transceivers is that the 100 kHz
IF transformers (bandpass filters) are misaligned slightly, so the response
isn't quite flat over the notch filter tuning range. Re-alignment of the last
IF may help.
--
73,
Scott K9MA
sdelling@facstaff.wisc.edu
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