[GreenKeys] Might be a bad weekend...

[David I. Emery]

On Sat, Dec 01, 2007 at 06:43:28PM -0500, Howard Weeks wrote:
> Some years back, the DCS HF networks sometime run up to 24 channels 
> of FSK TTY on one of the audio slots.  If my memory is not failing me 
> (and it may) each of these rtty slots used 85 cycle shift.  I 
> remember some that were set up for 100 cycle shift.  All of it fit 
> into one audio channel on the system which had to have pretty linear 
> response to keep down distortion from intermod products.  

	Back in the 60s when I was a young and foolish pup in HS and
then college I used to monitor all kinds of RTTY traffic off those HF
"tone packs".   At one time there were a gazillion point to point HF VFT
circuits that banged in on the east coast (Maine, NY and MA for me) and
back in this era (at least mid to late 60s) all the Navy Fleet
broadcasts were VFT tone pack as well (before the UHF satellite PSK
era).

	The ones I was familiar with were mostly 16 channels spaced at
170 Hz with 85 Hz shift for each channel.   There was a standard for the
tone frequencies and essentially all the military/government signals
seemed to use it.   Some other VFT signals on HF back then used other
tone spacing including mixtures of wider shift synchronous ARQ signals
and narrow shift TTY channels.

	Some signals ran ISB and had either another tone pack or a voice
circuit on the other sideband.   A few had  suppressed carriers (down
maybe 20 db) as pilots for receiver tracking, others had no carrier. 
And there were a few (notably some used on the AF Eastern Test Range -
Cape Canaveral/Antigua/Ascension) that had 4 voice channels rather than
two - usually with VFT on one or two and data and voice circuits on the
others.

	There were some similar tone pack VFT signals on LF, notably for
me  a really high power one from Nantucket at around 128 KHz (that is
from memory after 40 years or so, so it could be wrong by a few Khz).  
It ran only 8 tones rather than 16...

	Some of the signals used frequency diversity within the tone
pack with two tones (usually 8 tones apart) keyed with the same traffic.
And of course there were quite a few signals that used frequency
diversity at various times during the day with the same tone pack on
more than one RF channel.

	Most of the traffic was crypto most of the time, but many
signals carried wire service feeds (AP and UPI) and weather circuits,
and ITC orderwires and NASA ran many open circuits with RTTY traffic for
their tracking stations and ships in the clear.   And there were various
other odd things that showed up on these signals...
	
> Receivers were R-390s with some special sideband demodulators 
> followed by the multichannel TTY demodulators.  On the air, these 
> things sounded like a 4 engine piston airplane with the engines 
> slightly out of sync.  

	For years when I was VERY little (about 6-8) I thought these
signals WERE airplanes trying to talk over the engine noise (the voice
circuits on the other sideband would be faintly audible...) and in
subsequent years I found quite a few other young hams who really did
believe they had something to do with airplanes or were some kind of
jamming.

	I used a R-390A and 51J3 for my signal explorations, but by the
mid to late 60s the military had the R-1051 for use with these signals
which had under 3 Hz frequency stability and accuracy... and well before
that various other exotic full rack synthesized HF receivers were in use
with VFT signals both at land stations and on larger ships.  A R-390A
was really pushing things to hold stable within the 10-15 Hz it took to
demodulate these signals with acceptable distortion.    The R-390As 
actually used with VFT signals had an outboard tracking demod (a CV-157
if I remember right) that tracked the partially suppressed carrier with
a mechanical servo (I kid you 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."