[RTTY] Decoder performance on crowded bands

[Bill Turner]

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On Wed, 30 Sep 2015 22:07:14 -0400, Anthony wrote:

>
>Enjoying the thread.  Not a skimmer user but this explains a lot of spots
>in Logger + that indicated call signs on frequencies that were not actually
>there.  I couldn't understand it, but now it makes perfect sense.

REPLY:

There is one other common cause for wrong frequency spots that has
nothing to do with skimmers. Stations using AFSK often spot the
suppressed carrier frequency instead of the actual transmitted MARK
frequency. If you suspect this, look either up or down 2125 Hz from
the spot. It could be up or down depending on whether they are using
USB or LSB. LSB is much more common so I would look down first. 

And some stations like me use tones other than 2125 Hz, but I use FSK
which always spots correctly. For me, 1275 Hz is more pleasant to
listen to. I would go lower if I could but that is as far down as my
radio will go. Sigh. 

By the way, there is a good reason why AFSK stations should NOT use
tones lower than 2125, having to do with audio harmonics not being
suppressed. 

73, Bill W6WRT