On Oct 3, 2013, at 11:59 AM, Vladimir Sidarau wrote:
> but I am not an expert in ASCII codes and cannot prove it at all.
Vlad,
Over the air, it would be ASCII code, not Baudot.
Baudot characters like R and Y are most critical and most prone to reception
error, in terms of intersymbol Interference (ISI) and multipath, since they
have alternating bits. And that is why you see RYRYRYRY used to tweak RTTY
reception (not really needed nowadays with reasonable software modems).
You can find the Baudot table here
http://en.wikipedia.org/wiki/Baudot_code
For the bit sequence, you can use Fig 16-1 of the ARRL Handbook (from the 2010
edition on).
You are anecdotally correct about TU, at least the T part.
An RTTY start bit is a 0 followed by the LSB of the Baudot character, the rest
of the 5 bits and followed by the stop bit (1).
So a T (including the start and one stop bit) would be keyed as 0000011. That
has minimal bit transitions (and thus less affected by ISI and multipath).
The letter O (0000111) is probably a tad better than T, and has even lower
keying sidebands than a T. The RY sequence produces the widest keyclicks, and
most prone to multipath.
73
Chen, W7AY
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