[RTTY] Bad AFSK

[Joe Subich, W4TV]

Elecraft have taken the lead on FSK bandwidth - thanks to W7AY, K0SM
and W0YK among others.  Lets hope other manufacturers follow quickly.

Yesterday evening as I was looking for some RTTY activity to try the
new Elecraft "narrow FSK filter", I stumbled across another terrible
AFSK signal.  It just happens to belong to a well known club so I
won't give the call here but I have contacted the trustee.

However, I've posted a screen capture from my P3 that clearly shows
what happens when over driving the mic input of an SSB transmitter at:
http://www.subich.com/BAD_AFSK.jpg (the last spike at about 14.0972
is a local birdie).

Note this transmitter has not only "second harmonic" energy at
+1 KHz/340 Hz shift and "fourth harmonic" energy at +2 KHz/680 Hz
shift, it also shows insufficient opposite sideband suppression (or
possibly IMD in the PA - it's impossible to tell which).

One simply *can not* run "all sliders to the max" and "all knobs to
the right" with AFSK.  Any manufacturer or individual who says to
do so is giving you bad advice.  Again, unless you have the tools
to make absolutely sure you are generating clean AFSK, *use FSK*,
the clicks are far less objectionable than 2nd/3rd audio harmonics
that are suppressed by -18 and -15 dB respectively.  This capture
was made during a fade - signal levels were generally much higher
and even the spurious signals were well above -73 dBm (S9+).

73,

    ... Joe, W4TV