I've noticed over the years that some manufacturers (for whatever reason)
have moved to use a 200Hz shift instead of the standard 170Hz shift. The
reason for the move is unclear, perhaps it is merely for simplicity.
Whatever the case, it is claimed that tuning between two stations, one
using 170Hz shift and the other using 200Hz, is not all that great. When
the tuning between the two is centered, there is an offset of only 15Hz.
(200-170 = 30; 30/2 = 15) In the days when filters were a lot broader,
this offset was insignificant. I think Chen will bear me out that under
strong signal conditions this offset doesn't matter.
The only time when such an offset is important is when very sharp filters
with tight skirts are used AND the signal strength is weak or fluctuating.
That would lead to more errors.
I've been using an SCS modem for years with 200Hz shift on AFSK and I don't
seem to have a problem decoding weak RTTY signals.
Any thoughts or explanation?
Thanks,
73 de Phil - N8PS
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|