por Patman » 01 Nov 2013, 12:44
Todo este texto es muy interesante:
"In 1964, production of the Nestor series of enciphered voice communications (KY-8 vehicular mounted, KY-28 aircraft, and KY-38 manpack) was begun, but over a year passed before the KY-8/38 reached Vietnam in sufficient numbers, and even then few existed below battalion level. The Nestor equipment was sensitive to humidity and heat, and aircraft carrying KY-28s required frequent refitting. However, most of the problems involved the KY-38 because of its weight and bulkiness. The initial solution was to divide the communications gear, connected by a cable between two soldiers. During combat, the weakness of such an arrangement was obvious."
Ref The Most Secret War, govt. printing office, ISBN 0-16-051284-0, page 74.
"Initially reluctant to produce a cryptographic device for the combat infantryman that would undoubtedly be captured, the National Security Agency in January 1966 nevertheless agreed to develop a security device for portable radios. The National Security Agency and the U.S. Army Electronics Command designed the PRC-77, a modified PRC-25 that could be connected to the speech security gear." pg. 400
...
"In late 1967, after 15,000 PRC-25s and 7,000 models of the VRC-12 series radios were in the hands of American troops, and 9,000 PRC-25 models were being issued to the South Vietnamese Army, the Electronics Command produced an improved version of the PRC-25 even before the first PRC-25's had been sent to South Vietnam, the laboratories at Fort Monmouth were working to replace the power amplifier tube, the only vacuum tube in the set, with solid-state circuitry to lessen power requirements. They also added filters to reduce interference that later plagued communicators on crowded retransmission sites such as Nui Ba Den.
In December 1965 a means for connection with a security device, called an X-mode capability, was added to the specifications, and the new radio was designated the PRC-77. Although the Army had tested and produced the new radios to give the National Security Agency time to correct deficiencies in the companion security devices. Having had difficulties linking components of major assemblies in South Vietnam even when they were transported together, the Army wanted to issue the radios and security devices, the KY-38's (KY-28's for aircraft use), at the same time. The most serious problem encountered when the radios were finally fielded was the breaking of the cables connecting the radio to the security device. Then 500 replacement cables which had been quickly fabricated in a depot in the United States were lost in the crash of a cargo plane. The National Security Agency resolved another problem by developing a pressure-relief valve to preclude the buildup of hydrogen gas from the KY-38 batteries that had caused several KY-38's to explode after prolonged operations. By December 1968 modifications were completed, and over 9,000 new radios were in the hands of American combat radiomen." pg 448
Patricio
LW8DBP