Nordic Breeds WA4VZQ wrote:
I am sure Scott Dorsey knows more about this than I do, but CBS produced
two devices called the Audimax and Volumax that shifted the phase of the
audio as a function of frequency. Another term for these devices is
phase rotator. Kahn Communications also was in the market with its
SymmetraPeak. To the ear, the sound was unchanged, but to the
transmitter, the peaks became symmetrical. There is an excellent
discussion of these devices on James Tonne's (W4ENE) website
http://www.tonnesoftware.com/appnote...s/allpass.html and on Gary
Blau's (W3AM) website http://www.w3am.com/8poleapf.html. {A biased
opinion here — Jim's site contains some _excellent_ free software.}

The original Audimax/Volumax combination had no phase rotator. I worked
at an AM station that used them, and the chief engineer had installed a
phase reverse switch on the announcer mike and auditioned each announcer
to tell them which position to use. (Apparently they had used figure-8
mikes a year or so before I got there, and the announcers just used the
front of back of the mikes).

A lot of stations using the Audimax/Volumax would also have a phase
rotator in the chain, though. CRL made a popular one, and so did Garron.
Some folks made some boards tht dropped inside the Volumax for it too,
but I never used any of those. I went to the Optimod as soon as I could,
and it has a great phase rotator.

The phase rotator is a hell of a great gadget, it gives you a lot of loudness
without any perceived distortion. Mind you, for communications applications
it's no more effective just than aggressive clipping, but there are folks
who don't want aggressive clipping.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message
...
The original Audimax/Volumax combination had no phase rotator. I
worked
at an AM station that used them, and the chief engineer had installed a
phase reverse switch on the announcer mike and auditioned each
announcer
to tell them which position to use. (Apparently they had used figure-8
mikes a year or so before I got there, and the announcers just used the
front or back of the mikes).

A lot of stations using the Audimax/Volumax would also have a phase
rotator in the chain, though. CRL made a popular one, and so did
Garron.
Some folks made some boards that dropped inside the Volumax for it too,
but I never used any of those. I went to the Optimod as soon as I
could,
and it has a great phase rotator.

The phase rotator is a hell of a great gadget, it gives you a lot of
loudness
without any perceived distortion. Mind you, for communications
applications
it's no more effective just than aggressive clipping, but there are
folks
who don't want aggressive clipping.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


Thanks for the corrections, Scott.

Aggressive clipping creates a ton of distortion unless the voice signal
is split into several bands, each processed and filtered, and then
combined. The phase rotator theoretically produces no amplitude
distortion, and due to the way the human ear works, the shifting of the
phases is not heard. I read once that the cochlea and its nerves
perform physiologically something akin to a mathematician performing a
Fourier analysis. I find it amazing that we process sound, for the most
part, on the amplitude versus frequency information, and ignore the phase
versus frequency information.

With modern operational amplifiers, it is fairly simple to produce a good
phase rotator using cascaded all-pass networks. I would hate to have to
manufacture the original SymmetraPeak with its inductor-capacitor network
lattices.

Well, we are pretty far from the original subject, but I have enjoyed the
discussion. However I do have a Boatanchor question.

I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer and
how it worked?

73, Barry WA4VZQ

Nordic Breeds WA4VZQ wrote:

Aggressive clipping creates a ton of distortion unless the voice signal
is split into several bands, each processed and filtered, and then
combined. The phase rotator theoretically produces no amplitude
distortion, and due to the way the human ear works, the shifting of the
phases is not heard.

Right. I think for communications use, though, the ton of distortion can
actually help intelligibility of consonants under bad conditions. Certainly
it gives you a distinctive sound in a pileup.

I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer and
how it worked?

I have only heard of the echo-effect box. "Everything I use must have
X in it, like sex and echoplex" says Lee Scratch Perry.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article ,
says...

I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer
and how it worked?

I have a feeling it's another name for Lincompex, developed by the
British Post Office in 1966. Bell labs in the US apparently then came up
with something very similar - which I seem to remember was named
"Echoplex". Could be wrong - it was all a long time ago.....

Lincompex stands for LINKED COMPRESSOR and EXPANDER. The audio is
heavily compressed, and the pre-compression amplitude variations are
used to frequency modulate a 2900Hz control tone. This is combined with
the compressed audio (300-2700Hz) and fed to the TX. At the other end of
the circuit, the control tone is used by an expander to restore the
original amplitude variations.

Lincompex was used widely on international point to point SSB and ISB
voice circuits - and may still be in use (?)

The equipment was made by Marconi, and possibly ST&C (as was, before
Nortel bought them up).

You are both right.

On a 1966 issue of QST magazine, I found the advertisement of "Echoplex" by Kahn
Research Laboratories. It sold for more than 300$, which was not cheap at those
times.

As to Lincomplex, I remember a friend of mine working for Page Europe who told
me having installed Lincomplex on HF transmitters in Africa.

73

Tony I0JX
Rome Italy

"Antonio Vernucci" wrote in message
...
You are both right.

On a 1966 issue of QST magazine, I found the advertisement of
"Echoplex" by Kahn Research Laboratories. It sold for more than 300$,
which was not cheap at those times.

As to Lincomplex, I remember a friend of mine working for Page Europe
who told me having installed Lincomplex on HF transmitters in Africa.

73

Tony I0JX
Rome Italy

Thank you, Tony.

Somehow, I think you are talking about Leonard R. Kahn of Kahn Research
Laboratories in Freeport, Long Island, NY, and not A. Q. Khan of Khan
Research Laboratories in Kahuta, Pakistan (Pakistan's main nuclear
weapons laboratory as well as an emerging center for long-range missile
development). Leonard Kahn is best known for his paper: L.R. Kahn,
“Single Sideband Transmission by Envelope Elimination and Restoration,”
Proceedings of the IRE, Vol. 40, July 1952, pp. 803–806., and for his
work on AM stereo. Google somehow doesn't know the difference...

73, Barry WA4VZQ

"Nordic Breeds WA4VZQ" wrote in message
...
"Antonio Vernucci" wrote in message
...
You are both right.

On a 1966 issue of QST magazine, I found the advertisement of "Echoplex"
by Kahn Research Laboratories. It sold for more than 300$, which was not
cheap at those times.

As to Lincomplex, I remember a friend of mine working for Page Europe who
told me having installed Lincomplex on HF transmitters in Africa.

73

Tony I0JX
Rome Italy

Thank you, Tony.

Somehow, I think you are talking about Leonard R. Kahn of Kahn Research
Laboratories in Freeport, Long Island, NY, and not A. Q. Khan of Khan
Research Laboratories in Kahuta, Pakistan (Pakistan's main nuclear weapons
laboratory as well as an emerging center for long-range missile
development). Leonard Kahn is best known for his paper: L.R. Kahn,
“Single Sideband Transmission by Envelope Elimination and Restoration,”
Proceedings of the IRE, Vol. 40, July 1952, pp. 803–806., and for his work
on AM stereo. Google somehow doesn't know the difference...

73, Barry WA4VZQ

Wow, isn't this a super thread? Learned more here in a week of spare
time than 60 years of experiments and reading magazines! Where was
Usenet when we needed it?

Old Chief Lynn, W7LTQ

Somehow, I think you are talking about Leonard R. Kahn of Kahn Research
Laboratories in Freeport, Long Island, NY, and not A. Q. Khan of Khan Research
Laboratories in Kahuta, Pakistan (Pakistan's main nuclear weapons laboratory
as well as an emerging center for long-range missile development). Leonard
Kahn is best known for his paper: L.R. Kahn, “Single Sideband Transmission by
Envelope Elimination and Restoration,” Proceedings of the IRE, Vol. 40, July
1952, pp. 803–806., and for his work on AM stereo. Google somehow doesn't
know the difference...

Yes, it was Leonard Kahn. I have an Kahn SSB adapter for 455-KHz IF receivers.
It employs a great deal of nuvistors. Very complex machine!

73

Tony I0JX