More on ALE


Andrew J. O'Brien <obrienaj@...>
 

Hey, looks like fun...never tried it though.

I found more info....

General Overview:
Automatic Link Establishment (ALE) is the principle where a specialized
radio modem, known as an ALE adaptive controller, is assigned the task of
automatically controlling an HF receiver and transmitter in order to
establish the highest quality communication link with 1 or multiple HF radio
stations.

ALE controllers can be found as external devices (such as pictured above,
the Harris RF-7210A) or as imbedded options in modern HF radio equipment.

Link establishment is dependent on many factors and is fully optimized by
the use of a micro computer in the ALE controller. What follows is a basic
description of how ALE functions as the in-depth workings of ALE can be
elaborate and complicated to illustrate.

ALE controllers function on the basic principles of LQA (Link Quality
Analysis) and SOUNDing. These tasks are accomplished using the following
common elements.

Each controller has a pre-determined set of frequencies programmed into
memory channels.
Channels are continuously scanned (typically at a rate of 2 channels per
second).
Each controller has a pre-determined set of call signs programmed into
memory which includes its own station call sign (SELF), NETwork call signs,
GROUP call signs and INDIVIdual call signs.
ALE controllers transmit LQAs which SOUND the programmed frequencies for
best link quality factors on a regular, automated or operator initiated
basis.
When listening, ALE units log station call signs, frequencies heard on, and
assign a RANKing score relevant to the quality of the link on a per channel
basis.
When a station desires to place a call, the ALE controller attempts to LINK
to the outstation using the data collected during ALE and SOUNDing
activities. If the outstation's data has not been collected by the sending
ALE, the controller will seek the station and attempt to LINK using all
programmed channels.

Upon a successful LINK, the ALE controllers will cease the channel scanning
process and alert the operators that the system has establish a connection
and that stations should now exchange traffic. Upon completion of a LINK
session, the ALE controllers will send a LINK TERMINATION command and the
ALE units will return to the scanning mode awaiting further traffic.
Built-in safeguards also insure that ALE controllers will return to the SCAN
mode in the event of loss-of-contact.

As well as being capable of LQA and Optimum Working Frequency channel
selection, modern ALE controllers are also capable of sending short (87
ASCII characters long) orderwire digital messages known as Automatic Message
Display (AMD) to ANY or ALL members on the network. ALE controllers can
contact individual stations by their call sign, ALL stations, or ANY
stations on the NETwork or GROUP. ALL call and ANY call make use of
wildcard characters in substitution for individual call sings such as @?@
(ALL) and @@? (ANY). NULL Address Calls are used for system maintenance
and are sent as @@@.

Waveform:
ALE controllers conform to MIL-STD-188-141A link establishment functions and
perform encoding and decoding of data by the use of an 8-ARY binary FSK
modulator/demodulator.

Compatibility:
Not all ALE controllers are compatible. Further developments have now
produced 2 generations of link controllers mainly referred to AUTOLINK I and
AUTOLINK II. The second generation controller is both downwards and upwards
compatible with the first generation controllers as long as the
compatibility features are enabled in the system software. The basic
difference between the first and second generation units is in the type of
addressing utilized. Call signs in the generation 1 controllers are limited
to numerical digits (i.e. 112358) and call signs in the generation 2
controllers can employ up to 15 alphanumerical identifiers (i.e. UUT or
UNIT1 etc...).

Reliability:
Research indicates that equipment employing ALE technology over a set of 10
to 20 HF frequencies dispersed across the spectrum can raise the probability
of communication (above 95%) to a distant station several thousand
kilometers away to nearly that of SATCOM systems.

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