Automatic Link Establishment (ALE)
Automatic Link Establishment (ALE) is a technology that takes the guesswork out of choosing the best frequency to use to contact a specific station. Stations on an ALE network periodically send out a signal that identifies the station. This is called sounding. The sounding message is digital and contains error correcting data.
ALE stations scan a set of frequencies on numerous bands. When an ALE station receives a sounding on one of those frequencies it performs a link quality assessment (LQA) and stores the assessment in a table along with the frequency on which the sounding was received. If a received signal (sounding) was a good strength and required no error correction the LQA will be a high number. If the signal strength was low or required error correction to restore the digital message the LQA will be a lower number. The weaker the signal or the more correction required, the lower the LQA.
To call an ALE station you press the call button on the radio. It is usually marked with a large green handset. The radio prompts you for the station you wish to call which must already be in the radio’s database. Most radios allow you to add stations to the database on the fly. The radio may have additional prompts:
- The radio may prompt for the network to use. A network is a collection of ALE frequencies shared by other ALE radios on the same network.
- The radio may prompt for your call sign. You may have more than one call sign to choose from, such as a tactical call sign.
- The radio may prompt you to choose from a list of frequencies or choose “automatic” which allows the radio to choose based on the LQA database. Good radios will present the LQA data for each frequency as you scroll through the list.
Once the prompts have been finished the radio begins calling the destination station. If that station answers a link is established and the radio shows you that a link has been established. At that point you are free to use the microphone for a voice contact or a modem or sound card software for a digital contact. ALE’s job is done when the link is established. At the end of the session you generally press a button on the radio to break the link and resume scanning. A link timeout can optionally be set in case this final step is forgotten.
Software has been written to give ALE capability to ordinary HF amateur radios using CAT control of the radio and a sound card interface for the sounding and linking signals. As of this wiritng the software is free and is supported by a yahoo discussion group.
Generally, an ALE radio is silenty scanning the pre=determined net frequencies when no link is established. If a call is received the radio alerts the user and communication begins. This is, to many, much better than listening to static or constantly tweeking the squelch control during periods of inactivity.
Seasoned Hams generally understand propagation and know which frequencies are likely to be best for a given contact at a given time. But ALE removes all guesswork, allows unseasoned operators to choose the best frequency every time, and allows quiet monitoring of a network of frequencies until it is time to make or receive a call.
