Hz. These audio-frequency mark and space outputs are
referred to as “tones”; thus keyer one has a one-channel,
two-tone output.
A dc telegraph signal on channel 1 determines
which frequency is gated from the keyer to the group
attenuator. Each channel works in the same way. It
accepts a dc signal of marks and spaces from selected
equipments patched to that channel. It then provides an
audio output of either a mark or space frequency-shifted
tone, according to the input.
The individual tones are combined at the control
attenuator into a composite tone package. The control
attenuator ensures that the composite tones remain at a
constant amplitude for modulating the transmitter.
At the receiving end of the communications link,
the AN/UCC-1 reverses the process performed at the
transmitting end. The AN/UCC-1 applies the
information on each of the channels to the selected
equipments connected to the converter of that charnel.
In a frequency-division circuit configuration, each
channel has an input from a different teleprinter. If a
channel fades at a particular frequency, the information
on the channel could be lost or distorted. In such cases,
the information may need to be retransmitted. To help
prevent this, diversity switches that will permit the use
of more than one channel for the same intelligence are
available.
In switch position 1, only the normal channel is
used. In position 2, a single teleprinter signal provides
input for two adjoining keyers. In position 4, four
keyers are connected to the same input loop. The
switches on all keyers must be in the same position to
provide the same intelligence to the selected
combination of channels.
When identical intelligence untransmitted on two or
four channels, it is less likely to be lost or distorted. At
the receiving end, two or four corresponding converters
may be used; the converter having the stronger signal
input automatically provides the signal to be used by the
receiving teleprinter.
In the fleet broadcast multiplexing system, which
consists of 16 channels, 2 channels normally carry the
same intelligence. This process is called twinning.
Another method of multiplexing mentioned earlier
is time-division multiplexing (TDM). In this method, a
digital input is fed to a TDM unit. Here, it is
multiplexed into a composite intelligence stream for
transmission. The output is sent to an end user, where it
is broken into its original individual inputs.
However, instead of splitting the frequencies as in
frequency-division multiplexing (FDM), TDM shares
time. Each input uses the full bandwidth of the assigned
frequency but is assigned unique time portions of the
system. Figure 1-10 illustrates the front panel of a full-
duplex time-diversity modem.
SHIP-SHORE CIRCUITS
As we mentioned earlier, the fleet broadcast is the
primary means for delivering messages to afloat
commands. This section discusses a few of the other
types of circuits by which a ship can transmit its
message traffic ashore or to other ships for delivery or
relay.
SHIP-SHORE CIRCUIT MODES OF
OPERATION
There are three methods of operating
communications circuits: duplex, simplex, and
semiduplex. The mode of operation at any given time
depends upon equipment and frequency availability.
Duplex
Duplex describes a communications circuit
designed to transmit and receive simultaneously. In
such operations, each station transmits on a different
frequency and both stations transmit concurrently. Both
Figure 1-10.—Full-duplex time-diversity modem.
1-10
