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ALE in Ham Radio

For the past 7 years, a group of Amateur Radio operators has joined together for communications using ALE and Selective Calling. The number of hams has grown from just a handful active in 2001, to the thousands of enthusiasts in it today. Some are following the traditional ham curiosity to explore interesting aspects of communications; others are developing dependable HF nets, or just using it to keep in touch with a circle of ham friends. The need to call up emergency nets or inter-operability and liason with government HF systems has led many hams to adopt the government ALE standard, called FED-STD-1045 or MIL-STD 188-141. This standard caught on slowly in the ham community, initiated by a few operators with limited government surplus gear and some with expensive commercial equipment having embedded ALE or hardware controllers. Recently, the cost of embedded ALE transceivers has been reduced, and they are now available at similar to the cost of a medium priced ham radio. Also, with ALE software, a ham HF transceiver, a PC computer as the controller, and an appropriate antenna system, hams can harness the power of ALE.

How ALE Works

Each ham radio ALE station uses the operator's callsign as an address in the ALE controller.When not actively in a QSO with another station, each HF SSB transceiver constantly scans through a list of frequencies (called channels in ALE jargon), listening for its callsign. To reach a specific station, the caller simply enters the callsign just like dialing a phone number. The ALE controller selects the best available frequency and sends out brief selective calling signals containing the callsigns. When the distant scanning station detects the first few characters of its callsign, it stops scanning and stays on that frequency. The two stations' ALE controllers automatically handshake to confirm that a link is established and they are ready to communicate. The receiving station, which was muted up until now, will typically emit an audible alarm and visual alert for the receiving operator of the incoming call. It also indicates the callsign of the linked station. The operators then can talk in a regular QSO. At the conclusion of the QSO, one of the stations sends a disconnect signal to the other station, and they each return their ALE stations to the scanning mode. Some military / commercial HF transceivers are available with ALE options. Amateurs commonly use G4GUO's PCALE soundcard software interfaced to a ham transceiver via RS-232 CAT port, multi-frequency antenna.

ALE Using a Computer as the Transceiver Controller Unit
In 2001, Charles Brain G4GUO, wrote and released a soundcard PC program for ALE appropriately named PCALE. Charles is to be commended for his wonderful generosity and technical achievement. By doing this, he effectively opened up ALE to the non-professional user at low cost. The availability of PCALE in various improving versions made it possible for more amateur radio operators to start experimenting with ALE.

Ham Group for Coordinating ALE
During 2001, several hams in USA (including this author) started using PCALE, at the suggestion of Elaine WA6UBE. Elaine's already-operational Motorola Micom 2R transceiver (with embedded ALE) became one of the center points for testing and linking. In December 2001, from this core of early ALE operators,  HFLINK was founded by the author. The purpose of  HFLINK would be to further the development of methods and coordination for use of ALE and Selective Calling in HF Amateur Radio. HFLINK worked out guidelines for use and developed the digital programming protocols and standards for ham-friendly ALE. The scanning frequencies essential for effective ALE operation evolved and were coordinated with all IARU Regions of the world to become the International ALE Channel List.

Link Quality Analysis
For operation as an ALE system, the HF communications system normally has a number of  frequencies throughout the HF spectrum. The system works much like a telephone in that each radio in a net has an address (callsign or ID). When not in use, each radio receiver constantly scans through its various frequencies (channels), listening for calls addressed to its own callsign. To reach a specific station, the caller simply enters the desired callsign just like dialing a phone number. It takes a lot of time for the radio to go through the sequence of calling a station on every possible frequency. But there are several ways the ALE system can be programmed to decrease the time it takes, over simple random scanning and sequential channel calling. Methods for decreasing the time by using a "smarter" way of predictive or synchronized linking can be applied. An ALE system utilizing (Link Quality Analysis) capability uses periodic sounding and linking signals between other stations in the network, to stay in touch, and to predict which channel is best to call a particular station on at any given time. Various stations may be operating on different channels, and this enables the stations to find and use a common channel that is clear, that they both have.

Here’s how it works in an adaptive system using LQA. Once every hour or so, each station in a network will attempt to "sound" out each channel by sending a short transmission to all the other stations in the net, the transmission is its own callsign, and it may be sent on each of the channels it is operating on. All stations in the net who are scanning that channel may receive the sounding transmission and measure the signal quality on each channel for each other station IDs it receives. These signal quality "scores" are stored in a complex matrix of:

  • STATION ID
  • TIME DATE STAMP
  • CHANNEL NUMBER
  • SIGNAL QUALITY LEVEL
When a call is initiated to a station, the radio automatically checks its LQA matrix “memory” to make a determination of the most probable and best quality channel for the call to the desired station, based upon its record of recent Link Quality data it has logged on that station. It then makes its first attempted linking call on that most probable channel. If the link cannot be established, it will try again on the next best frequency in the matrix, and so on, until a link is established. Typical ALE systems using LQA make use of recently measured soundings or stations received within the past few hours.
 
---Bonnie Crystal, KQ6XA
HFLINK Founder



























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HFLINK is the international resource for ALE Automatic Link Establishment High Frequency Communications, HF Digital Messaging, Emergency / Disaster Relief, Interoperative HF Communications, HF Network, Ham Radio.