[GreenKeys] anyone using a two tone TU ?

Tue, 30 Mar 2004 11:04:18 -0600

Almost all TU designs use two tones; regardless of whether they are AM
(no limiter) or FM (with limiter).  Both approaches (AM and FM) still
have their place.  As you pointed out, limiterless operation tends to
work better when RTTY is sent at full machine speed. Where as the FM
variety (with limiter) works well with either full machine speed or hunt
and peck.

But there are situations where Limiterless (AM) mode is preferred no
matter what the speed.  When there is deep fading, an FM (with limiter)
TU will capture and amplify the noise in a channel when the signal fades
below the noise level, leading to errors in the copy.  An AM TU
(limiterless) will often copy right through these deep fades
particularly when equipped with the ability to dynamically copy on a
single channel or both channels.

My experience has been that for most situations, the FM type will do the
best job on the majority of signals.  But when deep fades and multipath
signals start causing errors, I usually switch to AM (limiterless)
operation with an improvement in copy.

TU's like the Hal's ST-6000 and ST-8000 can operate in either mode for
maximum flexibility.  However, Hal primarily focused on developing the
FM (with limiter) approach where Dovetron was the champion of the AM (no
limiter) approach.  For maximum flexibility, you need both.  For causal
listening, I would chose FM.\

Best regards -- Roy Norris, K4EEG

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stan Wilson
Sent: Tuesday, March 30, 2004 2:28 AM
To: [email protected]
Subject: [GreenKeys] anyone using a two tone TU ?

Anyone running an AM or limiterless TU design from the 60s?

I believe the weakness of the two tone AM design was hand typing but
with so many running RTTY today using

a computer plus the use of diddle I would think the limiterless version
of a TU would really stand up and do it's thing.

What has been anyone's experience ?

Thanks, Stan ak0b

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