Ron Baker, Pluralitas! wrote:

"msg" wrote in message
...

Greetings:

Seeking opinions on an old, commonly heard signal (AM) on HF, of some

snip

Thanks Ron for your detailed reply. Some folks have reported those
signals to be loud and harsh (high power) and not associated them
with airplane engine sounds, as was also my impression of them -- the
transmitters must have been nearby or very high power but who were
the users (in a non-suburban town of 30,000 people why a dozen or
more such signals)? As I had mentioned, I lived near a large Army
training camp and thus suspected a military origin but also wonder
if they had commercial users such as news wires to the media
(newspaper, radio), telephone company, etc.

There are many utes using OFDM these days.
They sound similar but sound more flat,
more whitenoise-like. I've heard them at:
4.28480
snip freq. list

Please listen to two examples I just recorded, the filenames encode
the freq. and date/time:

http://www.cybertheque.org/homebrew/rcvr/audio

I have heard this mode even on WEFAX frequencies during idle times.
It is certainly pervasive on HF and not at all like the old signals.
I had assumed by the spectral quality and frequency hopping
character of some examples that this was a sort of spread spectrum
signal.

Anyone hearing an example of older VFT signals currently on the air, please
post a freq. and/or record some audio.

Regards,

Michael