Portable Satellite Communications Link
February 1967 Electronics World
you are - portable satellite communications in the mid 1960s. I guess the definition of "portable" has changed a bit
[Table of Contents]
People old and young
enjoy waxing nostalgic about and learning some of the history of early electronics. Electronics World was published
from May 1959 through December 1971.
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Electronics World articles.
Portable Satellite Communications Link
one thinks of a satellite communications station, what usually comes to mind is a massive parabolic antenna coupled
to a large structure housing a formidable complex of electronics. During the past couple of years, however, many companies
have succeeded in putting together a highly sophisticated satellite communicator in a very small package. In many
cases, these stations are capable of being transported by conventional cargo aircraft to the desired site and then
being set up and placed into operation within a few hours by a crew of only half a dozen men. Such a typical station
is the Mark V AN/TSC-54 Satellite Communications Link Terminal developed by Radiation Incorporated and shown in the
The entire system consists of the antenna portion, which is capable of collapsing down into a small
package on its own trailer; an electronics shelter containing all the operating equipment; and a lightweight 45-kW,
400-Hz diesel generator. Total over-all road weight, including crew and sufficient fuel for 72 hours of operation,
is 12 tons, which, if desired, can be broken down into discrete 3-ton packages for air transport. Set-up by the six-man
crew, time from arrival at the site to actual communications is two hours.
The unusual-looking antenna has
four 10-foot Cassagrain aluminum reflectors, with the outboard section of each vertical pair of dishes capable of
folding laterally on hinges to make the antenna transportable.
Each feed emits its energy through a cone-shaped
foam dielectric material extending out to a small sub-reflector at the end of the feed. Because of the guiding effect
of the foam material, signal losses to the sub-reflector dish are reduced and over-all antenna efficiency is improved.
Gain is 52 dB at 8 GHz transmit and 51 dB at 7.25 GHz receive.
The antenna is a phase-monopulse type using
a special phase shifter which adds and subtracts azimuth and elevation error signals with the sum signal in such a
way as to permit the use of conical-scan signal processing in the receiver. These signals are used to drive servo
motors which control the tracking movements.
The air-conditioned electronics shelter can handle multiplexed
voice, Teletype, and facsimile, either directly from on-board equipment or from remote field equipment linked to the
terminal by an appropriate communications system.
The desired combination of signals is achieved using frequency-division
multiplex; this combination is then employed to frequency modulate a 70-MHz carrier, which is passed to the electronic
equipment in the antenna pedestal base. The signal is next up-converted to a specific frequency in the 8-GHz band
and amplified to 7 kW by a klystron.
In the receive mode, the antenna electronics converts the 7.25-GHz input
signal to the i.f. and then passes this down to the remainder of the receiver in the electronics shelter.
the equipment is set up and under power, the operator must then locate a satellite. The problem of locking onto a
satellite is intensified by the relatively narrow beam width of the antenna (0.3°) and by the fact that the ground
terminal's exact location may be unknown. When the operator presses a button, the antenna begins to follow a programmed
scan pattern very rapidly. Each satellite is identified by means of a coded beacon signal. If, during the antenna
scan, the ground system intercepts a satellite beacon, a relay doses and an integrator (position memory) directs the
antenna to the position where the signal was spotted. If the beacon signal is not detected within two minutes, the
automatic scan is resumed. If it is detected, automatic tracking begins. The received beacon signature first identifies
the particular satellite; then the ground operator selects the appropriate frequencies to be used for that satellite
and proceeds to transmit and receive messages.