Guys,
If you think an AFSK signal is a "clean" signal, do the math.
Most rigs are advertised as having -50 to -60 dB unwanted sideband
suppression. However, in practice, they average about -45 dB. An S-unit is
generally
accepted at 6 dB.
45 divided by 6 = a little more than 7, but let's call it 7 S- units.
So, an S9 FSK signal has no unwanted garbage (aside from key clicks).
An S9 FSK signal STILL can be heard 2.125 kHz away at S2 to S3 !! That's
louder than a lot of QRP signals.
Feed that into a linear amp with 10 dB gain and that unwanted sideband signal
gets up into the S5 to S6 level.
If you have a wonderful xcvr with -60 dB unwanted sideband suppression and
you're running an amp with 10 dB gain, you're still at S2 or better.
Of course, if you had such a wonderful xcvr, it would probably have
provisions for direct Frequency Shift Keying.
As others have suggested, if a person HAS the possibility of running FSK
instead of AFSK, it should be done.
In NO WAY is this meant to put down anyone who runs AFSK. It's just a
discussion of what is really happening.
73
Mike
W0YR/4
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