[GreenKeys] TU design

[Jeffrey Angus]

Having been playing with RTTY since the early '70s, I've watched
the development of TUs over the years.
 From the one tube "poor man's TU" which was, honestly, horrible.
To the HAL ST-8000A which was one of the best.

The most reliable TUs used a pair of filters. One for the Mark
tone, and one for the Space tone. And they were operated as a
dual diversity receiver. One for each frequency.
Where they got clever, was in the decoding. With AGC of sorts
and an automatic threshold sensor, then comparing the Mark
and Space decoded levels and making a decision by comparing
then and deciding the result as either Mark or Space.

-- 
"I am a river to my people."
Jeff-1.0
WA6FWI
www.foxsmercantile.com