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Figure 2-16.—Basic tone-modulated (AFTS) system. | Up
Electronics Technician Volume 03-Communications Systems | Next
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SIMPLEX RFCS TELETYPE SYSTEM
A simplex communications circuit consists of a
single channel, which may have two or more stations
communicating over it. However, they cannot
communicate at the same time. The stations have to
alternate using the channel.
RFCS teletype systems are used in the lf to hf band
for long-range communications. To reduce fading
and interference, the Navy uses two methods of
diversity reception called space diversity a nd
frequency diversity. In space diversity reception, the
transmitted signal is received by two or more antennas
spaced at distances greater than one wavelength.
Because of the spacing requirements, space diversity is
normally limited to shore stations. In frequency
diversity, two or more signals are transmitted on
differing frequencies, but carry the same intelligence.
Another type of frequency diversity is called af
diversity or tone diversity and is used with
multichannel broadcasts.
A simplified block of a simplex RFCS system is
shown in figure 2-17.
Figure 2-17.—Simplex RFCS system.
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