I have noticed that when I switch in my 500 Hz 9 Mhz RTTY filter, I can
still see strong signals that are out of the filter's passband on my
waterfall display. With my uncalibrated S-meter I can estimate that the
strong signals are S4 to S5 while the weaker signals are S2 or thereabouts.
Let's say anywhere from an 18db to 36db difference in signal strength. I
thought that these filters would reduce a signal outside of their passband
by at least 60db.
These strong signals can be eliminated by using passband tuning... but what
does this indicate? That the filter isn't doing its job? That there is
some path by which enough of the out-of-filter-passband signal is 'blowing
by' the filter? That, even at a 60db reduction in strength, since the
background is also reduced by 60db the fine receiver of the Omni VI is able
to copy that signal?
- jgc
John Clifford KD7KGX
Heathkit HW-9 WARC/HFT-9/HM-9
Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
Ten-Tec Omni VI/Opt1
Alinco DR-605TQ
Icom T90A
email: kd7kgx@arrl.net
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