MICOM-3F/3T/3R HF-SSB Owner’s Guide
34
Using Automatic Link Establishment
(ALE)
The MICOM-3 unit supports the Automatic Link Establishment (ALE) function, a method that enables
automatically selecting the best working channel from a group of preprogrammed channels without
any user intervention, thereby facilitating communication among HF radio stations and improving the
communications quality and reliability. The ALE incorporates all the advanced data transmission
techniques required by MIL-STD-188-141B and FED-STD-1045.
The ALE function ensures the best possible link without requiring prior knowledge of radio
communication conditions, and thus enables reliable HF communication even under rapidly changing
propagation conditions. For this purpose, HF radio sets using the ALE function continuously monitor and
evaluate the transmission quality on each frequency assigned for communication, and automatically
select an optimal frequency for each transmission. After selecting the optimal frequency, a link between
the communicating stations is established via an automatic handshake process, which is performed
without requiring operator’s intervention.
ALE combines sounding, scanning, selective calling, channel selection and LQA (Link Quality
Analysis). These features, all automatic, ensure that communication takes place on the channel with
the best link quality, even with an unskilled operator. The ALE also includes many types of calls you
can use to rapidly and efficiently set up links with other ALE users, and features such as messages,
stack and quick call.
The following sections present an overview of MICOM-3 ALE capabilities and services, and then
provide instructions on using ALE.
ALE Capabilities and Features
Scanning
The method used to select the best channel is based on scanning: as long as it is idle, a radio
operating in the ALE mode switches frequency at a relatively rapid rate (programmable at 2 or 5
channels per second) within the group of channels that can be used (the ALE frequency table, with up
to 100 frequencies). During this process, it collects information regarding the state of each channel
(busy/free and its background noise) that can be used together with the quality information collected
by sounding when the user initiates a call.
•
When a station initiates a call, it selects the best free channel on the basis of the most recent
information, switches to that channel and then transmits a call request for a time sufficient for
any station to finish scanning all the preprogrammed channels and reach the selected channel.
•
Any station that should receive this call will then stop on the channel used by the initiating
station, and will use the channel for communication. The exact response to the call request
depends on the type of call (call types are described below): as a result, it is possible to program
any desired station to ignore some types of calls (in fact, any call not specifically addressed to it).
Sounding
Automatic sounding is the method used by ALE for testing the quality of channels and propagation
paths under field conditions. The sounding signal is a unilateral identifying broadcast, repeated at
periodic intervals on unoccupied channels.
