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

[David I. Emery]

On Sat, Feb 17, 2018 at 03:43:22PM -0800, Richard Knoppow wrote:
>    The multiplex signals sounded to me like machinery running. 
> Not to be confused with the Russian jamming stations that sounded 
> to buzzsaws. They were also very strong. There were many 
> multiplex signals on the West coast. I thought at the time they 
> might have been coming from one of the commercial communications 
> services like RCA in San Francisco but they were probably the 
> Navy. It seems to me that there was a very large shared site near 
> Dixon Ca, with Navy, commercial, VOA, Telco and probably other 
> stuff. These days I hear mostly power line noise.

	The US military/gov kind of VFT was 170 Hz spaced 85 Hz shift
and either 8 (some signals on LF) or 16 channels mostly.  Depending on
whether you were hearing it in AM or SSB mode (BFO on or off) it sounded
like a droning sound or roar.  Even in SSB mode the individual tones
were hard to make out and it wasn't easy to hear them as FSK signals
though if you listened carefully as you tuned across the signal the
tones on the ends of the complex could sometimes be heard as FSK RTTY
sounding signals that sort of seemed mixed up with the drone signal as
if they were actually a narrow shift signal right near the droner.  But
they weren't - they were the upper or lower tone of the complex and not
something else nearby.   Very obvious on a spectrum plot.

	There was also quite a bit (around here) of RCA commercial HF
VFT which used mixes of wider FSK and sometimes 4FSK  signals with ARQ
TDM muxed 2 and 4 channel complexes on  them.  Sometimes these were
interspersed with narrow single channel traditional FSK tones. The ARQ
stuff (which was wider shift, 240 Hz or 400 or 600 Hz wide channels if
my foggy brain remembers any of this right) was constantly keyed and DID
sound like some kind of machine running with a constant sort of
repetitive tinkling sound and since these signals *WERE* FDM muxed
complexes on ISB, there were usually three or 4 or more of the ARQ
signals packed right next to each other in a voice frequency channel
making for a sort of audio soup of rapid tinkling FSK sounds.   The
wider shift of these signals made it possible for the ear to hear them
as separate FSK'd tones... they did not sound at all like a drone or
roar.

	Where I lived I rarely heard what I was sure was Russian jamming
in this era... and when I did it was in the SWBC bands and you could
usually hear some hint of radio station audio under it.    The VFT
signals were never (well almost never) in bands allocated to SW
broadcasters... and did not sound like actual jamming.

	Not sure what a buzz-saw sound means exactly, but some of the
strong US gov/mil VFT did have a sort of buzz-saw sound and I do
remember being told by various ham and SWL friends that strong, even
overpowering, signals I KNEW were 85 HZ VFT complexes were obviously the
USSR jamming something.   Indeed if you didn't know what the signals
were it was a pretty logical assumption that that roaring sound was
intended to jam something rather than carry information.   And I have
often heard others describe the VFT signals as sounding like a buzz-saw..

-- 
  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."