Embraer EMB145 Operation Manual page 2337

NAVIGATION AND
AIRPLANE
COMMUNICATION
OPERATIONS
MANUAL
HF COMMUNICATION SYSTEM - HF-230
The airplane may be equipped with a HF-230 High-Frequency
Communication System. All functions of the HF-230 System are
controlled by the CTL-230 Control Panel located at the control
pedestal.
HF OPERATING MODES
The HF-230 High-Frequency Communications System provides the
following operating modes:
AMPLITUDE MODULATION
Amplitude modulation (AM) is a transmission process in which a
selected frequency (called carrier frequency) and two sidebands
(frequencies above and below the carrier) are generated and
transmitted. The upper sideband (USB) is the sum of the carrier
frequency and the voice, while the lower sideband (LSB) is the
difference between the two. The disadvantages of AM are that it
occupies a wide spectrum and is inefficient in the sense that a great
deal of unneeded carrier is generated, as well as redundant
information in the unused sideband.
SINGLE SIDEBAND
Single sideband operation achieves the same function as AM with
considerably greater efficiency. The SSB transmitter electronically
eliminates most or all of the carrier wave and one of the sidebands.
The major advantages of SSB (either USB or LSB) as opposed to AM
are greater talking power (about eight times that of AM for a given
power input), reduced power drain, longer range and conservation of
the spectrum (since only one sideband is required to transmit the
message).
Page Code
1 01
2-18-21
JUNE 29, 2001