BendixKing KHF 990 - Manual (Page 22)

SIMPLEX AND SEMI-DUPLEX OPERATION
The KHF 950/990 is capable of both simplex and semi-duplex opera-
tion.
Simplex operation means that communication signals are transmitted
and received on the same frequency. Simplex operations are used
when communicating with Air Traffic Control (ATC), for example.
Semi-duplex operation means that messages are transmitted on one
frequency and received on another. The HF operator selects sepa-
rate transmit and receive frequencies, then keys the microphone to
transmit and releases the push-to-talk switch to receive. Semi-duplex
operation is usually used for maritime radiotelephone (public corre-
spondence) communications.
AUTOMATIC LINK ESTABLISHMENT (ALE)
ALE is an HF radio management system that selects the optimum
frequency of transmission, places automatic or manual calls to link
one or more users, and communicates digital messages. The ALE
specification and waveform were adopted as standards by the US
government in September, 1988 as MIL-STD 188-141
A (Appendix A)
for the military and as Federal Standard 1045 for civilian government
agencies.
The advent of ALE technology has changed HF communications by
allowing systematic and automatic real-time evaluation of HF com-
munications paths, permitting automatic frequency selection.
Because of this, the operation of an HF radio with Automatic Link
Establishment is greatly simplified and the communications reliability
is increased. A KCU 1051 CDU is required when Automatic Link
Establishment features are desired.
FUNCTIONS OF HF RADIO AUTOMATION
There are many functions, that the HF Radio Automatic Link
Establishment System performs for you. They are Selective Calling
and Handshake, Scanning, Sounding, Polling, and Link Quality
Analysis and Channel Selection
SELECTIVE CALLING AND HANDSHAKE - The selective calling
and handshake function enables the establishment of a link between
two radios. It includes digital address selective calling, followed by an
exchange consisting of a response and acknowledgment, to produce
a handshake (the establishment of a communications link).
Description
1-11 KHF 950/990 Pilots Guide
Rev. 0
Dec/96