[RTTY] Distortion

[W0YR at aol.com]

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