A standalone ALE radio combines an HF SSB radio transceiver with an internal microprocessor and MFSK modem. It is programmed with a unique ALE address, similar to a phone number (or on newer generations, a username). When not actively in contact with another station, the HF SSB transceiver constantly scans through a list of HF frequencies called "channels", listening for any ALE signals transmitted by other radio stations. It decodes calls and soundings sent by other stations and uses the bit error rate to store a quality score for that frequency and sender-address.