BendixKing KHF 990 - Manual (Page 23)

SCANNING - All available stations continuously and rapidly scan
their receivers through their channels, seeking ALE calls. At any
time, a calling station may slowly scan its transmitter through their
channels, calling on each one, until answered on a channel that sup-
ports contact. This function enables the selection of a channel that
successfully supports contact, despite variations in propagation,
occupancy, and other traditional HF challenges.
SOUNDING - Sounding is a special beacon-like technique that
assists all listening stations in measuring the propagation from the
sounding station. The sounding station transmits its address on all
channels, and the other stations measure the quality of the received
signal. Sounding stations provide this service to other stations and
do not use the information themselves.
POLLING - Polling enables two radios to measure the propagation
characteristics for each channel’s receive and transmit path. Then the
information is stored in non-volatile memory.
LINK QUALITY ANALYSIS AND CHANNEL SELECTION - This
function enables the radio to measure the quality of the received sig-
nals (and thus the available links) and to select the best channel for
calling and communicating. This function allows a calling station to
initiate calling on the best known working channel and thereby speed
linking. It also minimizes unnecessary calling on marginal channels,
when a transmitting station knows how well its signal is being
received by the intended stations.
HOW ALE ASSURES THAT THE BEST COMMUNICA-
TIONS LINK IS CHOSEN AUTOMATICALLY EVERY TIME
With Automatic Link Establishment on the job, the radio constantly
scans the available channels for an ALE transmission. ALE trans-
missions are digitized HF signals. When an ALE transmission is
detected, the signal-to-noise ratio of that signal is retained in memory.
The next time a call is made, the radio uses that signal-to-noise ratio
to determine the best channel to use. This way the best channel is
always the one used, allowing you to have the best possible commu-
nications link all the time, in spite of the constantly changing thick-
ness, density, and reflectivity of the ionosphere (a condition that is not
controllable). Every frequency reacts a little differently to random
changes in the ionosphere. The link quality for one frequency may
increase while it may decrease for another for the same random
changes.
Description
1-12 KHF 950/990 Pilots Guide
Rev. 0
Dec/96