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Characteristics Of Hf Ssb Communications; Hf Ssb Communications; Frequency; Appendix A - Honeywell KHF 1050 Pilot's Manual

Hf communications system with ps440 control display unit
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APPENDIX A

CHARACTERISTICS OF HF SINGLE SIDEBAND
COMMUNICATIONS

HF SSB COMMUNICATIONS

High frequency single side band communications achieve reliable long
range transmission and reception over distances of thousands of miles.
The primary reason is due to skywave propagation which allows HF
radio waves which are beamed toward outer space to be reflected back
toward the earth's surface by the ionosphere. Another reason is
because of a transmission process known as single sideband which puts
all the transmitter's power into sending just a radio wave containing the
intelligence to be communicated. Both of these make HF radio highly
useful to aircraft flying over water or desolate land areas when they are
out of reach of VHF communications which are limited to line of sight
transmissions.

FREQUENCY

The frequency of a radio wave is the number of cycles of that radio wave
which pass a given point within one second. The longer the wavelength,
the lower the frequency. The frequency is often expressed as cycles per
second, with one complete wave representing a cycle. The term hertz
(Hz) is more commonly used today to represent one cycle per second.
Expression of the measurement Hz has a shorthand of its own. When
thousands of Hz are expressed, they are designated kilohertz (kHz),
and millions of Hz as megahertz (MHz). Thus, the notation 29.9999
MHz represents a signal which is passing a given point at 29,999, 900
cycles per second. Expressed in kHz, the same figure would read
29,999.9 kHz representing 29,999.9 thousand cycles per second. In
using HF, you will encounter both MHz and kHz notations for frequen-
cies.
The high frequency (HF) band covers from 2.0 MHz to 30 MHz (2,000
kHz to 30,000 kHz). The HF band lies between the medium frequency
(MF) band and the very high frequency (VHF) band. Pilots are familiar
with the characteristics of MF frequencies through the use of ADF equip-
ment and know that these signals hug the ground and are sensitive to
variations in terrain and to atmospheric disturbances. On the other hand,
pilots know that VHF frequencies such as are used in VOR navigation
and normal communications with Air Traffic Control facilities generally
travel line-of-sight range and are not greatly affected by atmospheric dis-
turbances. As will be discussed next, HF has its own characteristics
which allow long range communications to take place.
15
Revision 0 Mar/2003
KHF 1050/PS440 Pilot's Guide

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