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Recorded Audio: AM or SSB ?




 
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Author Topic: Recorded Audio: AM or SSB ?  (Read 1472 times)
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KA2PTE
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« on: February 21, 2022, 08:17:37 PM »

This has been a project a couple yrs dabbling.

Curious if anyone is familiar about the types of scrambling used in
military or private type radios, as I have a vintage tape recording
where 2 stations are transmitting in perhaps a scrambled type of audio....or maybe SSB
or possibly overdriven AM.

At first I thought it was SSB, then was advised that since its on a very old
70's cassette tape, the tape material has degraded, lost its properties and is the reason
why there is this kind of distortion present.

Since then I have had a few audio professionals try to clean it up to no
avail. Then I noticed the cass tape housing was missing the felt pad inside that
presses on the play head when in play mode. I thought that was the entire issue, but after an entire
transplant of the tape into a new housing with the felt pad, the noise and distortion is still
there. A segment of the audio
 can be heard in a wave and ogg file here:
https://www.mediafire.com/file/xo8nw1vbyigpbvo/Airstrike.zip/file

Couple weeks ago I played more of the tape and about half way through, the 2 stations
get in touch with another 2 stations
and they are heard perfectly, but anytime the other 2 stations transmit,
they are still distorted and not very readable
which is why I think this is perhaps a secure scrambled channel between them I believe.

Thought maybe some of the older vets around that did radio back then may be
able to know for sure if its a scrambler or maybe a way to clean it up.

I was told is sounds more like overdriven AM, when 2 stations are too close in proximity
and the front ends are overloaded, but then I think they would not be able to converse at all
and they sound like they have a solid qso.



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CW is just a narrower version of AM


« Reply #1 on: February 21, 2022, 10:23:20 PM »

Back in the 80's two companies were merged and I worked for the new one. One of them was Controlonics of Westford MA, one of Dodge Morgan's companies (Whistler radar etc..). He also was that guy who sailed around the world solo. He had like 10 failures and 2 successes and still ended up with millions. Anyway, among other audio devices, Controlonics. They made voice scramblers mostly multiband inversion types. The market was fishermen who needed to communicate but not have other boats show up.
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KA2PTE
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« Reply #2 on: February 22, 2022, 01:37:38 AM »

Yep inversion was something bought up as a possibility. There is a video out there showing someone
who made a home brew scrambler using this method but it does not sound like a perfect match.
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w3jn
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« Reply #3 on: February 22, 2022, 08:22:30 AM »

Thats not speech inversion scrambling, which sounds exactly like listening to, for example, a station transmitting LSB when you have your receiver set to receive USB.

Looking at the file in audacity, it's severely clipped.  Seems to be either a problem with the tape, or the original recording - someone had the gain up too high on the recorder.  Probably not recoverable.
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KA2PTE
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« Reply #4 on: February 22, 2022, 02:23:37 PM »

Yea thats been bought up before by some others.

These 2 guys are pilots on I think close flying aircraft to each other on a mission to viet nam in the 70's.
Later in the tape they hit some kind of checkpoint(s) and theres chatter heard as they enter that airspace
and the other 2 stations sound fine. But the local pilots are always distorted.

I plan on moving the entire recording to mp3 at some point so that can be heard and the rest in entirety.

I did mess with audacity's clipping tool, and at some point playing with the settings, some parts cleaned up
and I thought I was onto a good recovery, but its definately complex.

Thats not speech inversion scrambling, which sounds exactly like listening to, for example, a station transmitting LSB when you have your receiver set to receive USB.

Looking at the file in audacity, it's severely clipped.  Seems to be either a problem with the tape, or the original recording - someone had the gain up too high on the recorder.  Probably not recoverable.
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WB6NVH
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« Reply #5 on: February 25, 2022, 05:50:57 AM »

In my experience in military helicopters based on carriers in the Vietnam era there was a scrambler in an ugly gray box with a padlock on it and a nameplate saying "NSA" with a model number of KY- something wired to the ARC-51BX UHF aircraft radio.  No way you will decode the audio from one of those with hobbyist equipment.

I have a matched set of Lynch scramblers in Samsonite attache cases circa 1970.  These are rather complex things with a telephone handset and digital code keys made of plug-in circuit cards.  There are interfaces for either a home phone line or a Motorola VHF mobile radio (and a 12V power cable.)  Those saw diplomatic use and there's no way you would decipher those with simple equipment (or at all, actually, unless you were the CIA/NSA or KGB with a full lab and a staff of engineers.)

In police service in the early 70's we had Motorola "Voice Privacy Adapters" which were simple voice inversion devices that you could indeed decode easily with some simple gear.  At least one scanner accessory company sold a "decoder" for that purpose.  Never found any crooks who knew that, however.
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Geoff Fors
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« Reply #6 on: February 25, 2022, 10:50:30 AM »

WB6NVH said:
Quote
In my experience in military helicopters based on carriers in the Vietnam era there was a scrambler in an ugly gray box with a padlock on it and a nameplate saying "NSA" with a model number of KY- something wired to the ARC-51BX UHF aircraft radio.  No way you will decode the audio from one of those with hobbyist equipment.
That was the box that held the permutator cards. They held a key code that was changed daily like Mode 4 IFF, NTDS Link 11 etc. I know, I was a CMS custodian and changed the codes daily on ship.
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Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
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« Reply #7 on: February 25, 2022, 03:25:03 PM »

You jogged my memory, I recall that now! 
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Geoff Fors
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KA2PTE
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« Reply #8 on: May 18, 2022, 12:52:34 PM »

I contacted the Air Force vet who is one of the voices on the distorted recording, and I mentioned
it may be scrambled audio, but he seems VERY certain there is no scrambler onboard.

If it were the degraded magnetic material on the tape, I think the other voices coming in later
as they check into the waypoint station would be distorted the same too.

Im starting to think as someone else mentioned, there is just overdriven input to the recording head.
So that ought to be not too hard to resolve...
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