[GreenKeys] RTTY receiver noise immunity?

[Nick England]

I’ve been in a discussion with the USS Iowa guys about what to expect when
there’s no RTTY signal just receiver noise. They are concerned because they
get a bunch of garble when there’s no signal and the AGC turns up the gain.

Note. This discussion is not about noisy RTTY signals but responding to
noise when there is NO RTTY signal.

I am fairly new to RTTY but use vintage equipment.  It seems normal to me
that some noise will trigger the space filter and the TTY will print some
random characters every now and then, more often or almost continuously if
the noise level is high. The same discussion holds true for autostart I
guess.

OK, software or complicated digital hardware can do all kinds of things to
mitigate random characters, but what about earlier TUs? What is your
experience from the olden days (or today using vintage gear)?

I can see a couple of non-software strategies
1) SELCAL with a M28 stunt box. The TTY still cycles but doesn’t start
printing until the correct sequence of characters arrives.
2) manually riding the receiver RF gain to keep noise low when there is no
signal
3) having a receiver with squelch or COR (carrier operated relay)
4) use a multivibrator to Mark hold unless a space pulse is at least 22ms
long.
5) use a multivibrator to Mark hold until there is a  long Space or Mark
signal. Typical autostart circuit I guess.

Or???


-- 
Nick England K4NYW
www.navy-radio.com
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