[Milsurplus] overheard telephone conversations

[George Babits]

Sure, I remember the "bagpipes."  By the way, A-3 was the older designation 
for AM.  A-1 = CW; A-2= MCW, A-3= AM.  Things were a lot simpler back then. 
I also remember endless 5 letter crypto groups on both CW and RTTY.  Thot 
would ahve been in the early 1960's.

73,
George
W7HDL


----- Original Message ----- 
From: "John Vendely" <jvendely at cfl.rr.com>
To: <milsurplus at mailman.qth.net>
Sent: Tuesday, May 31, 2016 6:39 PM
Subject: Re: [Milsurplus] overheard telephone conversations


> On 5/31/2016 6:50 PM, AKLDGUY . wrote:
>> The consensus seems to be that WW2 necessitated encryption
>> and spurred on its development, but there's nothing to suggest
>> that 1937 radio telephone calls were made unintelligible to the
>> casual HF listener.
> Those circuits using the aforementioned A-3 would have been unintelligible 
> to and virtually unbreakable by the casual listener. A-3 was commonly used
> by Bell for commercial traffic, not just military.  So far as I can 
> determine, in the late thirties Bell was using both SSB and AM on 
> transcontinental HF telephone circuits.
> I suspect they used mainly SSB for their own circuits, and may have used 
> full carrier DSB AM where needed to be interoperable with other systems, 
> though I'm speculating here.
>
> Needless to say, Sigsaly mainly used SSB; it probably was almost a 
> necessity, as this system operated with essentially zero margin. It's 
> really remarkable that it worked as
> well as it did.  I seem to remember reading somewhere that on a few 
> Sigsaly circuits DSB AM was used as an expedient (perhaps on the shipborne 
> systems?), but I can't be certain.  I've seen very little written about 
> the radio links themselves.  I wonder if anyone else has found anything on 
> this?
>
> I do recall hearing some conventional AM international telephone circuits 
> on HF into the late 1960s and early 70s, though most everything was SSB by 
> then.
> One AM system in particular was said to be between Cuba and the USSR, and 
> used some kind of speech inversion technique.  I remember hearing this 
> system frequently
> from the mid 1960s, and upon occasion maybe as late as 1975.  It had a 
> peculiar channel marker mode in which an odd little electronically 
> synthesized melody with a reedy
> sound reminiscent of bagpipes played endlessly in the absence of traffic. 
> The carrier would drop momentarily between repetitions of the melody.  Any 
> one else remember
> hearing this thing?
>
> 73,
>
> John K9WT
>
>
>>
>> It doesn't even seem clear whether SSB was used. Terrestrial
>> telephone links certainly used upper sideband in broadband
>> Frequency Division Multiplex systems pre-war, as I pointed out
>> in an earlier post where I described the Western Electric crystal
>> filters. I just now recalled that those filters had the ring modulator
>> or demodulator (depending on speech direction) built-in, together
>> with impedance matching transformers.
>>
>> 73 de Neil ZL1ANM
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