Manual
Table Of Contents
- TITLE PAGE
- TABLE OF CONTENTS
- INTRODUCTION
- SECTION I
- CHARACTERISTICS OF HF SSB
- ACRONYMS AND DEFINITIONS
- REFERENCES
- HF SSB COMMUNICATIONS
- FREQUENCY
- SKYWAVE PROPAGATION - WHICH FREQUENCY TO
- WHY SINGLE SIDEBAND IS IMPORTANT IN HF
- AMPLITUDE MODULATION (AM)
- SINGLE SIDEBAND OPERATION
- SINGLE SIDEBAND (SSB)
- SUPPRESSED CARRIER VS. REDUCED CARRIER
- SIMPLEX AND SEMI-DUPLEX OPERATION
- AUTOMATIC LINK ESTABLISHMENT (ALE)
- FUNCTIONS OF HF RADIO AUTOMATION
- HOW ALE ASSURES THAT THE BEST COMMUNICA-TIONS
- CHARACTERISTICS OF HF SSB
- SECTION II
- SECTION III
- SECTION IV
- SECTION V
- SECTION VI
- SECTION VII
- ITU MARITIME RADIOTELEPHONE STATIONS
- DESCRIPTION OF SERVICES
- AT&T HIGH SEAS RADIOTELEPHONE SERVICE
- AT & T COAST STATION COVERAGE MAP
- COAST STATION COVERAGE & INFORMATION
- AIRCRAFT REGISTRATION
- OPERATING PROCEDURES FOR USING THE HIGH SEAS RADIOTELEPHONE NETWORK
- AT&T HIGH SEAS COAST STATIONS
- MOBILE MARINE RADIO, INC.
- WORLDWIDE LISTING OF PUBLIC CORRESPONDENCE STATIONS
- MARITIME RADIOTELEPHONE CHANNEL DESIGNATIONS
- SECTION VIII
- SECTION IX
- SECTION X
- SECTION XI
- SECTION XII
- SECTION XIII
WHY SINGLE SIDEBAND IS IMPORTANT IN HF
COMMUNICATIONS
As mentioned earlier, there are two characteristics of HF SSB com-
munications which allow long range capability. Skywave propagation
has been discussed in detail. The other characteristic is a transmis-
sion process known as single sideband. Single sideband (SSB) high
frequency (HF) communications was developed in the early 1950’s
as a means of increasing the effective range of HF signals. The KHF
950/990 is capable of both amplitude modulation (AM) operation,
such as is used in conventional VHF aircraft communications, and of
SSB operation.
AMPLITUDE MODULATION (AM)
In order to understand SSB operation, a discussion of AM operation
is helpful. Amplitude Modulation (AM) is a transmission process in
which the selected frequency (called the carrier frequency) and two
sidebands (which are frequencies above and below the carrier fre-
quency) are generated and transmitted. (Figure 1-2.) It takes about
two-thirds of the transmitter’s power just to transmit the carrier fre-
quency, yet the carrier does not contain any of the intelligence to be
communicated. Each of these sidebands contains all the intelligence
to be communicated. Standard broadcast stations (550-1600 kHz)
and short-wave broadcasts use AM since it allows simpler receivers.
NOTE: The use of lower sideband isn’t normally authorized for air-
borne HF use. It is normally disabled in the KHF 950/990, but can be
enabled for those who are authorized to use it.
Description
1-9
KHF 950/990 Pilots Guide
Rev. 0
Dec/96
AMPLITUDE MODULATION (AM)
fc = carrier frequency
fm = modulating frequency (voice)
fc-fm
LSB
fc fc+fm
USB
Figure 1-2 Amplitude Modulation