BendixKing KHF 990 - Manual (Page 13)

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. A familiarization with fre-
quency, skywave propagation, amplitude modulation, single sideband
operation, suppressed carrier versus reduced carrier, simplex and
semi-duplex operation, and automatic link establishment will make
this pilot’s guide easier to use and understand.
The following explanations will help provide a base to build on as you
acquire experience in operating your KHF 950/990. If you have had
experience with HF radio previously, the following material will serve
as a review.
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 represent-
ing 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 mega-
hertz (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 repre-
senting 29,999.9 thousand cycles per second. In using HF, you will
encounter both MHz and kHz notations for frequencies. KFS 594 and
KCU 951 control display units always express frequencies in terms of
kHz. The KCU1051 control display unit always expresses frequen-
cies in terms of MHz.
The high frequency (HF) band , with which we are primarily con-
cerned in this pilot’s guide, covers from 2.0 MHz to 30 MHz (2,000
kHz to 30,000 kHz). The HF band lies between the medium frequen-
cy (MF) band and the very high frequency (VHF) band. Pilots are
familiar with the characteristics of MF frequencies through the use of
ADF equipment 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 affect-
ed by atmospheric disturbances. As will be discussed next, HF has
its own characteristics which allow long range communications to
take place.
Description
1-2 KHF 950/990 Pilots Guide
Rev. 0
Dec/96