[R-1051] R-1051 Speakers

[David I. Emery]

On Thu, Dec 12, 2019 at 10:39:26AM -0500, Nick England wrote:
> Possibly 85Hz shift on 170Hz spacing - that was the usual military VFCT
> (AN/UCC-1, etc) as well as commercial gear from Tele-Signal, etc.

	The wire services used a 60 Hz shift 22/24 channel mux instead
of the 85 Hz shift 16 channel common in military service (UCC-1 and
several later).

	The military standard was 85 Hz shift and 170 Hz tone channel
spacing in the mux - with 16 tones active in most cases.   This standard
was widely used on HF from the mid 50s or so until the 80s... as well as
on many wireline circuits used by the military and government and some
UHF and microwave/troposcatter systems.   It supported 75 baud (~100
wpm) tty circuits and that was the most common bit rate used with it,
either in various crypto formats or ITC Baudot.

	A commercial standard that emerged in the 60s based on the
military standard (and practice inside telcos) used 60 Hz shift and 120
Hz tone spacing.  This allowed 22 or 24 channels to fit in standard VF
audio wireline channels.   That represented a significant savings for
users sharing a common audio circuit, as more services could be stuffed
into the same line, reducing cost per channel and the number of different
"wires" that could be provided over one phone line.

	Commercial use of this technology for wire services and the like
mostly involved lower bit rates than 75 baud (45.42, and 50 baud  being
common) ... which allows narrower shifts and channel filters without
serious degradation of the signal distortion margins.  And commercial
use did not usually include circuits with lots of analog distortions
such as HF ISB signals and troposcatter FDM channels.   So it was quite
practical for most uses to use 60 Hz shift 120 Hz spaced channels even
for some 75 baud 100 WPM circuits with some small  degradation of
distortion margins.


-- 
  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."