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Single Sideband Operation; Suppressed Carrier Vs. Reduced Carrier; Simplex And Semi-Duplex Operation - Honeywell KHF 1050 Pilot's Manual

Hf communications system with ps440 control display unit
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SINGLE SIDEBAND OPERATION

By electronically eliminating the carrier wave and one sideband, a single
sideband transmitter manages to pack all of its power in transmitting the
remaining single sideband. (Figure 3A). Either the upper sideband
(USB) or the lower sideband (LSB) can be used since each sideband
contains all the required intelligence. However, from a practical stand-
point the USB is used almost exclusively in airborne HF SSB operations
and the LSB may be disabled. Upon receiving this SSB signal, the
receiver then generates the carrier frequency internally and combines it
with the one sideband in such a way that the intelligence (voice) can be
heard and understood by the pilot.
The result is that an SSB system has the effective transmit power of AM
units having many more times the transmitter power. Also, SSB commu-
nications allow the frequency band to be utilized more efficiently since
the space or "bandwidth" of only one sideband rather than two sidebands
is required to transmit the message.

SUPPRESSED CARRIER VS. REDUCED CARRIER

The single sideband (SSB) operation just described with the carrier fre-
quency virtually eliminated is actually referred to as single sideband sup-
pressed carrier. If just a small portion of the carrier is transmitted along
with the sideband, the operation is referred to as single sideband
reduced carrier.

SIMPLEX AND SEMI-DUPLEX OPERATION

The KHF 1050 is capable of both simplex and semi-duplex operation.
Simplex operation means that communication signals are transmitted
and received on the same frequency. Simplex operations are used
when communicating with Air Traffic Control (ATC), for example. Semi-
duplex operation means that messages are transmitted on one frequen-
cy and received on another. The HF operator selects separate transmit
and receive frequencies, then keys the microphone to transmit and
releases the push-to-talk switch to receive. Semi-duplex operation is
usually used for maritime radiotelephone (public correspondence) com-
munications.
Revision 0 Mar/2003
SINGLE SIDEBAND (SSB)
fc = carrier frequency
fm = modulating frequency (voice)
fc-fm
fc
LSB
Figure 3A - Single Sideband
22
fc+fm
USB
KHF 1050/PS440 Pilot's Guide

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