[RTTY] Spot frequency

[Ed Muns]

Gary, AL9A, wrote:
> I've read stuff about this before, but would appreciate it if 
> someone could refresh my memory.  During the DLDC contest I 
> was spotted several times by various stations.  Most spots 
> were at or very near my VFO frequency. 
> However, I noticed a few spots that were a couple of kHz 
> below or above my VFO frequency.  For example, while running 
> at 14082.75 (FSK) I was spotted at 14080.6.  Another time I 
> was spotted 2.1 kHz above my VFO frequency.
> 
> I seem to remember this was due to the 2125 Hz shift.  Is 
> this a difference between running FSK or AFSK?  In the 
> example above was that due to the spotting station running 
> AFSK on LSB?  What about the spots above my frequency?  AFSK 
> on USB?  And what about the spots I send out while using FSK. 
>  Are my spot frequencies correct or off too?  It was a bit 
> annoying to call CQ endlessly and finally see someone spot 
> me, but on the wrong frequency!  Can someone clarify this for me?

Discrepancy between your RTTY frequency and what is spotted by another
station depends on what each of you uses for a reference.  Most people use
their VFO frequency as what they spot.  Depending on whether that is the
Mark RF frequency or the suppressed carrier frequency of an AFSK
configuration (and whether they are using LSB or USB and what their local
audio tone frequency is), the discrepancy could be as much as 4.25 kHz.

The "standard" way to denote a RTTY frequency is by the Mark RF frequency.
This is independent of whether you transmit with FSK or AFSK, whether you
use LSB or USB and what your local audio tone frequencies are.  If the radio
displays the Mark RF frequency on the VFO display, then it is easy.  If not,
then it is likely displaying the suppressed carrier RF frequency, which
differs from the Mark RF frequency by +/- the local Mark audio tone
frequency.  In that case, you (or the other station making the spot) needs
do the mental arithmetic before stating the Mark RF frequency.

Of course, if both stations are configured identically, then all of this is
irrelevant and their radio VFO displays will be the same, or very close,
even if the frequency cited is not the RF Mark frequency.

73,
Ed
--------------
Ed Muns - W0YK
www.w0yk.com