[GreenKeys] Loop supplies. Again.

[Jeffrey D Angus]

At 45.45 baud, or 60 WPM, each signaling bit is 22 mS wide.
The range adjustment on a TTY machine is there to move the sampling
of the data bit plus or minus a few mS from the center of the data bits.
This is done to account for either Marking or Spacing distortion of the
signal.

Nominally, the range control sets the sample time to 30 mS after the
initial start pulse and then every 22 mS thereafter.

IF you're running too low a loop supply voltage, the selector magnet
will not pull in in time to be properly sampled as a Marking signal.

If you're running the local loop with a solid signal source with no
distortion, it will work with a 48 volt supply. If you're trying to copy
a marginal signal, such as "over the air RTTY" it will add enough
distortion to make garbled copy.

Original TTY loops were considerably longer than a few tens to
hundreds of feet, and radio circuits added their own distortion to
the signal.

If your signal source is a tape reader and a short local loop, or an
accurate audio signal into a terminal unit (like the audio from ITTY)
then you don't have as big a problem with distortion and can use
a lower loop voltage.


-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com