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AN/PRC-77
Portable military VHF transceiver - this page is a stub

AN/PRC-77 was a military portable VHF transceiver, also known as a backpack radio, introduced by the US Army in 1968 as the successor to the AN/PRC-25. The radio was used heavily during the Vietnam War, and differs from its predecessor in that its RF power amplifier stage (PA) is fully solid state, whereas the PA of the PRC-25 was made with thermionic valves (vacuum tubes) [1].

The PRC-77 consists of an RT-841 transceiver and some additional components, made by various companies. It is suitable for secure voice operation, by selecting the so-called X-MODE and adding an external voice encryption unit, like the KY-38 (NESTOR) or the KY-57 (VINSON).

For the European market, it was made by Telemit Electronic GmbH in München (Germany). Telemit improved the radio in several ways, including changing the channel spacing from 50 kHz to 25 kHz. As a result, the radio is still interoperable 1 with most modern military VHF radios today.
  

Both receiver and transmitter cover the 30-75.95 MHz frequency range, divided over two bands, in steps of 50 kHz (or 25 kHz for the European version). The receiver has a sensitivity of 0.5 µV, whilst the transmitter delivers between 1.3 and 4 Watts to the 50Ω antenna. The device measures 273 x 273 x 100 mm and weights 6.2 kg. It is powered by two voltages: 12.5V DC and 2.5V DC, which are usually supplied by military batteries (BA-4386/U, BA-398/U or BA-55984) [1].

  1. Not compatible with the SINCGARS frequency hopping mode (FH).

Voice encryption devices used with the PRC-77
Tactical voice encryptor (NESTOR) Wide-band Voice and Data Encryption Unit (VINSON) Hagelin CVX-396 (SVZ-B) voice encryptor Siemens MSC-2001
The following voice encryption units are known to have been used with the AN/PRC-77:

KY-57
KY-57 was a small tactical wideband voice encryptor that was developed in the mid-1970 by the US National Security Agency (NSA) as a replacement for the NESTOR devices (KY-38).

It features the highly secret SAVILLE encryption algorithm and was for many years the crypto 'workhorse' of the US Armed Forces.

 More information

  
KY-57 voice encryption unit

CVX-396
In the mid-1970s, Telemit added the CVX-396 voice encryption device to the European version, which was in fact a rebranded device made by Crypto AG (Hagelin) in Switzerland.

It has the same width as the PRC-77 and can be mounted on top of it. Note that it is less secure than the Swiss national version SVZ-B.

 More information

  
CVX-396 with open door

MSC-2001
MSC-2001 was a small tactical voice encryption unit, developed in the late 1970s by Siemens in München (Germany). It was initially developed especially for use with the PRC-77 radio, but was also suitable for other radio sets.

It can hold up to 8 different 50-bit cryptographic keys, selectable with a rotary switch at the front.

 More information

  
MSC-2001 voice encryptor

References
  1. RigReference, Military AN/PRC-77 Portable VHF Transceiver
    Retrieved March 2018.
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Crypto Museum. Created: Sunday 11 March 2018. Last changed: Sunday, 23 December 2018 - 10:06 CET.
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