Alan - Sorry I can’t help with your FT991 issues, but if you don’t mind me
hijacking the thread a bit, I would like to say a few things about weak signal
contesting using FM.
Below the capture threshold, usually about 10dB signal to noise ratio, FM
behaves much like other signals with amplitude, not frequency, modulation. That
is, there is a linear increase in demodulated signal strength for a linear
increase in input signal strength up to the capture threshold of about 10dB SNR
or so. So, there is usually useful communication ability if the squelch is
lowered to the point where it is ineffective in squelching the noise. You can
usually hear the station. The downside to operating in this region is the
increased bandwidth, which results in increased noise.
I have had many long distance QSOs on FM operating below the capture threshold,
mostly in AZ during the January contest when SOTA stations often operate from
mountain tops with low power handhelds. I remember one QSO of 90 miles or so on
1296 where the other station was having trouble hearing me. After several go
around, someone on frequency, who could hear both of us, kept telling him to
turn down his squelch. He finally did and we made the QSO.
About the only time I operate FM is during the contests, but I find listening
to a squelched radio unnerving. I expect to hear noise in the receiver when I
stop transmitting. It seems unnatural not to. How do you know it is working? -
Duffey KK6MC
James Duffey KK6MC
Cedar Crest NM
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