BDK wrote:

In article , _
says...

Greetings:

Seeking opinions on an old, commonly heard signal (AM) on HF, of some
considerable power, with a very memorable sound.

snip, see thread

It's called several terms FDM "Frequency division multiplexed" is the
most common term. Also called VFT. There are several formats.

It's basically a bunch of RTTY channels all blended together into one
signal.

Here is a purported sample of a VFT modulated signal (from a site with
digital mode sound samples):

http://www.kb9ukd.com/digital/vft.wav

One can hear at least one rtty channel and the background drone (of
FDM rtty 'spacing' on the other channels?).

This is pretty much what I thought VFT would sound like with low baud
rate channels; I can only extrapolate how faster rate channels would
sound and I suspect that it would be very multispectral. The signal
from the 1960s had only a few tones, closely spaced and harmonically
unrelated, was very much harsher sounding and these tones had a
phase-modulated characteristic sound with a period of about one second.
(and it was non-random in character, not like qpsk, modem noise, etc.)
The wide bandwidth it occupied didn't seem to be FDM related but
appeared to be a consequence of its high percentage of modulation
(and didn't appear to be restricted to one set of sidebands). It
contained no audible frequency shifting as one would expect from FSK
rtty. It may have been a self-clocked (manchester style) signal or
set of muxed signals.

One respondent suggested LORAN; even with the recent enhancements
I don't think the description of LORAN modes is much like my old signal
and the carrier frequencies are wrong.

Geolocating it would help to narrow down the potential
users of this signal; please, if you remember this signal, post a
message about signal strength and where you were located.

I will appreciate more recollections and comments

Regards,

Michael

In article Uaeoi.72$zJ4.4@trndny03, HFguy wrote:
LORAN?

Loran A was only around 1800 kHz and was a strange simultaneous
up and down zipping noise.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

"Ron Baker, Pluralitas!" wrote in message
...

"msg" wrote in message
...
Greetings:

Seeking opinions on an old, commonly heard signal (AM) on HF, of some
considerable power, with a very memorable sound.

This will be a bit difficult to describe and I wonder if some folks

snip

The sound on the air was much like hearing several P51 fighters
approaching at high airspeed and props not in phase; the spectral

snip


Regards,

Michael

I remember what you are talking about.
Back in the late 60's using a cheap shortwave
receiver we heard things such that we naturally said,
"That sounds like an airplane." Sounded like someone

snip

Most likely they were, as others have said, VFT or
something like it. They were almost certainly a

Propagation doesn't seem to have been that good
recently. (Height of summer I guess.)
But I managed to catch a VFT signal tonight at
11103 kHz. Switched to AM mode. It didn't sound
like what I remember from way back when.

Also found a signal at 8488 kHz that I think is
a mil-std-188-110 signal. Switch to AM mode. That
sounded more like what I remember from the
60's.

But mil-std-188-110 didn't exist in the 60's. Maybe there
were similar signals at that time.

Ron Baker, Pluralitas! wrote:

"Ron Baker, Pluralitas!" wrote in message
...

"msg" wrote in message
...

snip

Seeking opinions on an old, commonly heard signal (AM) on HF, of some
considerable power, with a very memorable sound.

This will be a bit difficult to describe and I wonder if some folks


snip

snip

Also found a signal at 8488 kHz that I think is
a mil-std-188-110 signal. Switch to AM mode. That
sounded more like what I remember from the
60's.

But mil-std-188-110 didn't exist in the 60's. Maybe there
were similar signals at that time.


I have recently located a friend from those days and the same town
who may also shed some light on this question. Also I do remember
lots of interference from medical equipment at the local hospital,
especially diathermy machines, which may possibly be the source
since the signals were _very_ strong, broadband, and at many
frequencies.

Regards,

Michael