THE LINCOLN EXPERIMENTAL TERMINAL
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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Lincoln Laboratory has designed and constructed three satellite communications ground terminals Lincoln Experimental Terminals as part of its program in space communications. The first of these LET-1 is a self- contained, transportable, X-band terminal in which the RF equipment, antenna and mount are on one vehicle, and the signal processing equipment, prime power and operating console are in a second van. The other two systems LET-2 and LET-3 consist of signal processors identical to that of LET-1. They are similarly housed in vans and are used in conjunction with antennas and RF equipment associated with other terminals. The three systems were completed in 1965 and tested extensively since that time, using active satellite repeaters and the moon as a passive reflector. The function of the terminals is to demonstrate satellite communication in which multiple-access and anti-jam performance are emphasized. The use of vocoders for speech compression and an efficient modulation and coding system for signaling result in a low required satellite power per access. Bandspreading by pseudorandom frequency hopping provides the desired multiple-access and anti-jam capabilities. This report is a description of selected portions of the system emphasizing the most novel features. The first chapter gives a general description of LET-1 as a whole, and the second an over-all description of the signal processing system. Chapter 3 discusses the equipmental realization of the signal processing system and Chapter 4 the utilization of a general-purpose computer as an element of the signal processing system. Chapter 5 and 6 treat two specific subsystems the sequential decoder and the vocoder.
- Radio Communications