[GreenKeys] Re:

[David I. Emery]

On Sun, Dec 02, 2007 at 10:18:36PM +0000, sdaitch at mor.ibb.gov wrote: > 

> We, at VOA Greenville, had some Northern Radio SS TTY mux units that
> may have been more for HF tone pack operations, since as best as I
> remember, there were some diversity options.  Early solid state gear,
> but we did not use them, instead we had earlier tube type NR systems on
> the VOA HF TTY circuits.  We did not use the full 16 channels, we used a
> high tone pair and a low tone pair, and the demod unit was also capable
> of diversity. Seems Type 107 rings a bell.

	Interesting.   Now you mention NR 107, I suddenly realize that
the tone filters I used with the somewhat modified Irv Hoff/Vic Poor TTL
II I first used to copy VFT WERE NR 107 tone filters I found surplus
somewhere.   I found a significant part of a complete set and I think
later eventually found the rest of the thing (it had plug in tone
filters on a little aluminum chassis along with a discriminator). The
tone filters were sealed in metal transformer cases and I think were 600
ohm in and out networks... substantially better shape and filter
performance than what one could easily do with 88 mhy toroids and a desk
calculator and set of filter tables (computer realization of such was
still more or less a dream in that pre-PC era).

	My hack to the TTL II design worked a lot better than the actual
NR 107 as I remember it... the ATC threshold correction and LPFs helped
a lot... copy off of 85 Hz shift mux channels was at least as good as off
170 Hz ham stuff with the normal filters in the original design.

	And I do remember copying 100 WPM Voa stuff from your feeder
signals... I guess what sticks in my mind about it was the required
repetition of negatives, every time the word NOT was used they said NOT
RPT NOT...


-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."