[Milsurplus] Helicopter Comms Intercept as referenced in "The Greatest Beer Run Ever"

[Mike Morrow]

The NESTOR voice encryption system was developed by the mid-1960s for use with Tactical FM and (much less commonly) military UHF-AM radio sets.

NESTOR crypto units were:

TSEC/KY-8     Ground fixed and mobile
TSEC/KY-28   Aircraft
TSEC/KY-38   Portable man-pack

The Army's most commonly used man-pack set up to 1968 was the AN/PRC-25, but it was not compatible with NESTOR.  The most important change made to its successor, the AN/PRC-77, was its redesign  for NESTOR.  The elimination of AN/PRC-25's one vacuum tube was of only incidental importance.

NESTOR-encrypted communication between all major Army units was thus NOT possible until the AN/PRC-77 showed up in 1968, along with the TSEC/KY-38 portable NESTOR unit.

The TSEC/KY-38 was almost the same size, shape, and weight as the AN/PRC-77.  The two units connected together with a couple of awkward external cables very subject to entanglement in vegetation.  Pity the poor RTO who carried it all plus his own packband weapon.  The KY-38 thus was extremely unpopular with its users.

After 1968 TSEC/KY-28 was installed on most Army combat aircraft.  A Command and Control UH-1 would have a KY-28 for its AN/ARC-54 or -131 Tac FM radio, plus a temporary console in the back with three AN/ARC-54 sets and TSEC/KY-28s.

Ground units had TSEC/KY-8 for some AN/VRC-12-series installations.

Among all users, NESTOR was unpopular due to voice transmission delay after PTT and distortion.   Great care had to be taken with the initialization process on all units prior to an operation.

The USN and USMC did not often use NESTOR in SEA, although the UHF-AM AN/PRC-41A was a modification of the -41 for NESTOR, and the KY-8 was on many USN ships including submarines for UHF-AM service.  It was not installed with PBR and PCF AN/VRC-46 sets, and I have never read of USMC use of NESTOR in Vietnam. (The USMC was mostly out of Vietnam by 1971 except for embassy security.)

NESTOR was replaced by VINSON (TSEC/KY-57) more than 40 years ago.  I don't have any idea what is used now.

Mike / KK5F

-----Original Message-----
From: Rob Flory <farmer.rob.flory at gmail.com>
Sent: Nov 1, 2022 2:52 AM
To: milsurplus <milsurplus at mailman.qth.net>
Subject: [Milsurplus] Helicopter Comms Intercept as referenced in "The Greatest Beer Run Ever"

I recently read this book, quite a story, and it had some radio content.
 
One of the author's friends had a job installing upgraded comms gear in helicopters because VC or NVA were intercepting or at least detecting helicopter comms with an ordinary FM radio.  
 
What was not clear was whether that meant a broadcast radio or an FM field radio of some kind.  
 
I believe helos were equipped with low band FM gear and that either:
 
1)captured or interoperable sets were used or
2)harmonics of the low band FM gear were detected on a relatively empty FM broadcast band. 
 
Option 1 would give legit intercept capability, which could be defeated by encryption.  Option 2 might give enough early warning capability to either disappear or assume a defensive posture.  Presence of signal, encrypted or not, might give the necessary warning.
 
Encryption would require the ground pounders to be encrypted also.  
 
Anyone know anything that might flesh out the story?
 
RF



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