[GreenKeys] on-off radio teletype (not FSK)

[David I. Emery]

On Sat, Feb 17, 2018 at 07:58:09AM -0600, Jim Haynes wrote:
> I'm talking about 1940s, early 1950s.
> I'm not sure when FDM on the radio started, but think it was late 50s
> or so.
> 
	I was born in 1948, so that era is mostly before my time... I 
do remember finding some papers in the mid to late 60s about early VFT
experiments and systems discussing work done with mux VFT as HF SSB
emerged in the middle 50s... I believe there was an increasing amount of
it used on strategic long haul HF circuits in that era and have seen
photos of fixed long haul com stations from that time with floor to
ceiling racks of 6U/8U  modulators and demodulators for it implemented in
vacuum tubes and heavy iron.   16 or 32 channels done that way could
easily occupy a couple of bays.. and those sites were loaded with R-390as
and CV-157s and other stuff to support the VFT.

	I also remember as a little boy in the early to mid 50s tuning
around on a 1940 pre WWII Magnavox SW console radio my parents owned and
hearing the very powerful continuous roaring airplane sounds - some of
the strongest signals on the bands...  while this was a long time ago
and memories shift and fade, a number of these same signals persisted
into the early to mid 60s when I was in HS and had advanced to having
model 15 and 28 machines and TUs and actually was able to demodulate and
print some of the traffic on them so I am fairly sure that what I
remember hearing earlier was VFT and not something else.

	But I was in the Boston area which was a hotbed of various
exotic experimental government communications R&D, and a fairly optimum
skip distance and angle for reception of all the HF transmitters aimed
at Europe around DC, PA, MD, and VA... and out on Long Island - and some
in Ipswich Mass as well... so there may well have been more of these
signals at very high level around me as part of strategic HF circuits to
Europe and the middle east than in many other places.

	I do understand that in the late WW II era and on into the early
50s there were lots of SigSaly signals around in my area - these were
described as sounding like the "Green Hornet" radio show intro audio...
and quite distinctive.    They supplied the first really
cryptographically secure HF digital voice circuits ever implemented, and
were used to communicate with European and Far East commanders... (and
of course Churchill and FDR).... and probably also sounded like what you
describe somewhat.   I would have to dig up a recording of one to see if
I ever thought I heard that... the system was only declassified MUCH
MUCH later... well after that stuff was off the air.

	And my area was the site of a pioneering direct sequence spread
spectrum HF system that provided anti-jam RTTY circuits to West Berlin
in the mid to late 50s... and that signal was also distinctive (and I do
remember it, as an odd fading white noise like peak)..  a lot of
important research came out of that... including RAKE receivers... and
all kinds of channel adaptive stuff.. much of it important to modern
digital comms.

	And finally of course there were quite a few of these continuous
HF SSB VFT signals used to communicate with things like the Texas tower
radar sites off the east coast, and BMEWS in Greenland and so forth.

	By the time the Navy took up this mode in the early 60s for the
fleet broadcast the TUs were all transistorized and 16 channels fit into
about the same rack space as a R1051 or two...  and of course by that
era many of the strategic HF circuits were being put on undersea coax
cables and sometimes troposcatter networks (and soon after satellites of
course)... and going off the air on HF.

	High speed Morse (or variants) was well known as a technique for
communicating with submarines which could surface or come up to some
depth where a HF antenna could emerge from the water and  transmit
messages in short bursts of very high speed CW before submerging
again... all before it was easy to reliably find or DF the signal.

	Famously the "elephant cage" wullenweber DF arrays were
developed to make finding and DFing these burst transmissions quickly
and reliably enough to locate and track the transmitting sub possible...
and the world wide Navy network of them for this purpose was installed
in the late 50s and early 60s for locating Russian subs - which has been
discovered to be using this technique to send in regular position and
status reports.  This high speed short burst CW mode for submarines was
something I  understand the Germans pioneered in WWII BTW.

-- 
  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."