[RTTY] Spot frequency

[Joe Subich, W4TV]

 > With all the tools at our fingertips, (including a calculator :-),
 > there should be no excuse for not spotting the mark frequency of an
 > RTTY signal properly.

That's the problem ... there are too many software authors who don't
care to educate their users and do not bother to provide the correct
frequency (if they provide any RF frequency at all).  These are the
same authors who say "don't worry about FSK - just run audio tones
into your mic in USB."

When you couple that with users who can't (or won't) read the manuals
for their transceivers - and transceiver makers who don't provide the
correct (mark) readout - it becomes a mess of confusing "standards."
As always when there more than one "standard" there is *no* standard.

73,

    ... Joe, W4TV

On 6/13/2010 9:01 PM, Kok Chen wrote:
>
> On Jun 13, 2010, at 5:18 PM, Gary AL9A wrote:
>
>> I seem to remember this was due to the 2125 Hz shift.  Is this a
>> difference between running FSK or AFSK?
>
>
> By convention, RTTY signals are identified by the Mark frequency.
>
> Most radios when operated in FSK mode will display the mark carrier
> as the VFO dial frequency.  So, the problem is most likely *not* be
> originating from you.
>
> But take the case of an AFSK op who just worked you (and presumably
> zero beat with you)...
>
> If his VFO dial is showing the suppressed carrier frequency of an LSB
> transmitter, and he using the 2125/2295 tone pair, then his (and
> your) mark carrier will be 2.125 kHz below his dial frequency.   If
> he is spotting from his VFO dial, the spot will read 2.1 kHz higher
> than your actual mark frequency.
>
> Now, what if he is using USB?
>
> In this case, assuming he is using the same 2125/2295 tone pair, his
> mark carrier will be 2.295 kHz above his suppressed carrier.  (Notice
> that the mark, by convention is always the higher frequency of the
> two RF carriers.)  If he is reading off a VFO dial that displays the
> SSB suppressed frequency, his packetcluster spot will then be 2.3 kHz
> too low.
>
> That said, good rigs won't have this problem if you set them up
> correctly.  The menu of the FT-1000MP for example, allows you to
> apply a dial offset to the AFSK ("PKT") mode.
>
> Even if the radio does not have that feature, software modems often
> have a place where you tell it to how to label the waterfall
> frequency. cocoaModem for example has a VFO offset box, plus a menu
> to tell it if you are using USB/LSB and it will apply the arithmetic
> gymnastics to display the number that has to be added to or
> subtracted from the VFO dial to get the actual frequency of your RTTY
> mark.  cocoaModem will in fact reverse the waterfall (lower tones
> appearing on the right side of the waterfall instead of higher tones
> always on the right) when you transceive in LSB so that the waterfall
> will show the higher RF carrier always to be on the right of the
> waterfall.
>
> With all the tools at our fingertips, (including a calculator :-),
> there should be no excuse for not spotting the mark frequency of an
> RTTY signal properly.
>
> 73 Chen, W7AY
>
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