msg wrote:

Greetings:

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

snip

Thanks for the replies. I was surprised to discover these posts from
an archived mailing list that described my signal in similar terms:

From Sat Sep 9 13:18:00 1995
From:
Subject: Coded Signal Identification ?
Message-ID: Chameleon.4.01.2.950908231744.jproc@jproc

Dear BA's,

Back in the 1960's, I remember hearing very loud signals in the HF bands
which sounded exactly like piston aircraft engines. Also evident, was a bit
of alternating Doppler shift in the sound. Someone once told me this was some
sort of high speed, coded message circuit. By the 70's or 80's, it looked
like all of these signals vanished from the bands.

Can anyone identify what I was receiving?

Regards,
-------------------------------------
Jerry Proc VE3FAB
E-mail:
Radio Restoration Volunteer
HMCS Haida, Toronto Ontario

From Sat Sep 9 13:18:00 1995
From:
Subject: Re. Coded signal ident.
Message-ID:

to:

Hello Jerry.

The "aircraft engine" signals you used to hear weren't necessarily coded.
These beasts were VFT, or Voice Frequency Telegraphy.

Essentially, they were stacks of 8, 16, or 24 narrow shift AFSK signals
that were used to modulate an SSB transmitter; i.e., they were multiplexed
RTTY.

The reason most of 'em disappeared (yes, there are still a few around) is
that these point to point circuits have mostly moved to satellite. BTW,
thereis a 50 channel version of the same scheme on the birds.

73's,
Tom, K9TA


From Sat Sep 9 13:18:00 1995
From: Steve Ellington
Subject: Re. Coded signal ident.
Message-ID: Pine.SOL.3.91.950909103627.2439A-100000@iglou


The "aircraft engine" signals you used to hear weren't necessarily coded.
These beasts were VFT, or Voice Frequency Telegraphy.

Aw nuts! When I was a kid I had it all figured out that those were
communist jamming stations. I would carefully tune around them trying to
hear the Jammed broadcast to no avail. Later on I just decided they were
really airplanes. Once, me and a buddy used that noise to record a skit
for a school play involving some aircraft.

I prefer to go on believing they are airplanes. :*o

Steve




At the time, I didn't associate the sound with aircraft engines since it was
much more discordant and had a very aggressive quality when heard on AM through
a wide filter. I used to hear the sound in nightmares...

If anyone has this sound preserved in recordings from that era, I would
appreciate the chance to hear it again and analyze it.

Regards,

Michael
msg _at_ cybertheque _dot_ org