MMTTY AFC, O-scope (Re: [RTTY] Re: Noise with MMTTY

[Bill Turner]

On Wed, 24 Mar 2004 10:58:09 -0600, Don Inbody wrote:

>In the Navy, when we used RTTY extensively, it was 850Hz shift, 100 baud.
>Of course, we also had the signal encrypted, so that required constant
>"diddling" to ensure the crypto remained synchronized.  
>
>My question is this: is there any proof that narrow shifts (170Hz for
>example) is better than wider shifts (850Hz) for resistance to phase
>shifting.  Also, what is the history as to why we settled on 45 baud 170Hz
>and not some other.  I know a lot of experimenting went on in the 1950s and
>1960s, but can't seem to locate the data.
>
>I did an experiment with 850hz shift the other night, but can't see that it
>is any better or any worse.

_________________________________________________________

According to Brian, K6STI - whose opinion I highly respect - the wider
shift provides more resistance to selective fading, as you mention
above.  I suspect, but don't know for sure, that 170 Hz was selected
because it just fits (including sidebands) in a 250 Hz filter, which has
been pretty common for years.  As to the 45 baud, it's about as fast as
anyone can type, so it accommodates the abilities of just about
everyone.

These are just my opinions; no scientific proof is offered.  :-) 

--
Bill, W6WRT
QSLs via LoTW