On Aug 25, 2013, at 9:33 AM, Bill Turner wrote:
> Chen, we'll have to agree to disagree on that point, but that was not the
> reason for my original reply to Kai's post. Kai said "The theoretical
> bandwidth of 170 Hz shift 45.45 baud RTTY is just under 250 Hz."
As an "emission designator," the ITU uses the formula
Baud + Shift*1.2
for specifying channel spacings ("neccessary bandwidths") of an FSK signal.
See here if you won't take my word for it:
http://life.itu.ch/radioclub/rr/ap01.htm
Scroll down to Part B in the above link, look for the class of "direct printing
telegraphy" as the representative formula.
The 1.2 factor is purely empirical. But if you follow the ITU formula
religiously, steam RTTY comes out as having a bandwidth of 249.45 Hertz.
You can quibble that Kai's number is off by a quarter percent from the official
ITU number, but Kai obviously rounded that ITU number up to 250 Hz. Indeed,
you often see Amateur RTTY specified with a "250H" prefix in its Emission
Designator.
Anyhow, you now know where Kai got the 250 Hz from, and it is not from his
backside, or I would have already called him out on it.
73
Chen, W7AY
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