[RTTY] Shift 170 -vs- 200

[Anthony (N2KI)]

I seem to recall that some of Europe was using a 200hz shift years ago, but
I could be wrong about this.  When selecting the narrow band filters, I
would be able to copy a 200hz shift signal on a 300hz filter and not very
well on a 250hz filter. I was able to copy the 170hz shift signal with the
250hz filter.  In lieu of this, I stopped using 250hz filters for RTTY and
subsequently gravitated to the 300hz filter allowing me to copy both 170hz
and 200hz shifts fine.  Again, I don't recollect this fully.  Please
enlighten me if this is not the case.  T


Anthony - N2KI
 www.n2ki.com

-----Original Message-----
From: rtty-bounces at contesting.com [mailto:rtty-bounces at contesting.com] On
Behalf Of Phil Sussman
Sent: Thursday, June 09, 2011 7:59 AM
To: rtty at contesting.com
Subject: [RTTY] Shift 170 -vs- 200

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



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