[GreenKeys] RATTS

[Howard R. Weeks]

Been running a crystal controlled AFSK generator to a KWM-2 running about
50 watts for many years.  I have learned the hard way several things:

1.  The tone source needs to be relatively low distortion.  If not, you have
a fat RF signal.
2.  You have to keep the drive levels to the SSB transmitter under control.
Push it too hard
and you have a fat RF signal.
3.  You have to have good carrier and opposite sideband suppression.

If you do this right, as Robert says, the spectrum analyzer will not tell
the difference.  In practice,
many operators do not get this right and you can always hear the difference
when they don't.

Howard Weeks
Harlem, GA


----- Original Message -----
From: <WA5CAB at cs.com>
To: <ehertz at tcaf.org>; <greenkeys at mailman.qth.net>
Sent: Friday, February 25, 2005 5:35 PM
Subject: Re: [GreenKeys] RATTS


The short answer is Yes.  Turning on the BFO produces a heterodyne (two
actually, but only one is in the audio region) which would then be fed to an
audio
type (not the only type, BTW) of receiving converter.

The most important thing that a mode switch does when you switch it to CW,
SSB, ISB, LSB or USB (depending upon how the receiver is built and how the
mode
switch is marked) is to turn on the BFO.

The short answer to your second question is No.  There would be no way to
tell the difference.

The longer answer would add the weasle statement "assuming that the
suppressed carrier was not strong enough to be detected by person C.  The
spectrum
analyzer (panadaptor) displays would be the same in either case.


In a message dated 2/25/2005 4:18:46 PM Central Standard Time,
ehertz at tcaf.org writes:
> Can one or can one not use "CW" mode in a receiver and apply a BFO against
> the shifting carrier? Shouldnt this work too? That to me (very very novice
> understanding of stuff) would really explain whats going on, making
discussion
> of USB and LSB moot, no?
>
> Here's a questions I have had for some time and now have the nerve to
ask...
>
> If someone were to use a spectrum analyzer to look at a "rtty" signal
coming
> in off the air, would they be able to tell if the signal was generated
> through ASFK or FSK? In other words, if person A were to apply an audio
shifted
> signal to a transmitter in (say) LSB mode, and another person "B" keyed an
fsk
> mode in a transmitter, do the signals they produce differ in any way?
Could
> person C tell which sender is using which mode?
>

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)
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