receiving system. With the path length and direction
fixed, propagation factors are simplified. This
provides highly reliable hf communications.
powered transmitters, lower noise receivers, and more
efficient antennas.
Fleet Broadcast
Ship-to-Shore
High-frequency atmospheric communications
between shore stations are relatively easy because
shore stations have sufficient space for efficient
omnidirectional antennas or arrays that provide hf
coverage of large areas. Ship-to-shore hf communica-
tions are more difficult because the ship is moving and
constantly changing direction. This change of
direction and severe space limitations aboard ships
make the installation of large, efficient hf antennas
impractical.
To overcome these problems, ship-to-shore
systems have two major differences from point-to-
point systems. First, shipboard antennas are omni-
directional. Second, several frequencies are usually
assigned for each circuit. If one frequency starts to
drop out, another can be selected to match the
propagation path conditions between the ship and the
shore terminal.
Ground-to-Air
The use of hf radio for ground-to-air com-
munications is similar to its use for ship-to-shore
communications. An additional problem is that an
aircraft moves much more rapidly than a ship. This
rapid movement (plus additional space limitations)
requires that all major circuit im-provements be made
at the ground stations. Examples of improvements that
can only be made to the ground station are higher
As the name implies, this service involves
broadcast area coverage from shorebased transmitters
to ships at sea. To overcome propagation problems,
messages are sent on several frequencies at the same
time (frequency-diversity). Space-diversity with
physically separated receive antennas also helps
overcome propagation problems.
Now let’s look at typical shipboard high-frequency
transmit and receive systems.
Shipboard HF Transmit
The high-frequency transmit signal can contain
either voice or teletype information. Figure 2-5 shows
a typical shipboard high-frequency transmit system.
The same equipment used to receive teletype
messages on low frequencies (teletype, DC Patch
Panel SB-1210/UGQ, crypto equipment, and DC
Patch Panel SB-1203/UG) are used to send teletype
messages on the high-frequency system; but of course,
in reverse order.
An AN/UCC-1(V) or CV-2460 telegraph terminal
converts a dc signal into a tone signal. This signal is fed
to the SB-988/SRT transmitter transfer switchboard. A
C1004 transmit keying and control/teletype is used to
key the transmitter during tty operation. Voice
communications also can be connected to the SB-988/
SRT switchboard. The voice communications are
developed at a handset connected to the C-1138 radio
Figure 2-5.—Shipboard hf transmit system.
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