4-12
SHIPBOARD RECEIVE-ONLY EQUIPMENT SYSTEMS
The purpose of a shipboard receive-only system is to receive fleet multichannel teletypewriter
broadcasts, which, as you recall from chapter 1, require no receipt. These are transmitted from a ground
station and relayed to naval vessels by satellite.
Figure 4-13 is a typical shipboard receive-only system. In this system the transmitted carrier may be
frequency modulated (fm) or phase-shift-key (psk) modulated for tty operation. The receiving antennas
for this system are positioned about the ship. They are arranged in a manner (normally one in each
quadrant of the ship) that at no time allows the line-of-sight to be blocked between the relay satellite and
one or more of the antennas. Incoming signals pass from the antennas to an amplifier-converter. Each
amplifier-converter routes an IF signal on one line of a twin axial cable that connects it to the combiner-
demodulator. An operating power and local-oscillator signal are coupled from the combiner-demodulator
to each amplifier-converter on the other line of the cable used for the IF signal. Because of signal path
variations, shading, and reflections, the incoming signals are subject to random phase and amplitude
variations. The combiner operation performed within the combiner-demodulator removes the phase
variations from each input signal. It then measures the amplitudes of the signals for optimum combining
and sums the signals. After being combined, the signal is demodulated and coupled from a receiver
transfer switchboard to a telegraph demultiplex terminal.
Figure 4-13.—Typical shipboard receive only system.
Q10. What is the function of shipboard receive-only equipment?
Q11. What types of modulation are shipboard receive-only equipment designed to receive?
