G7TXU

Selcall is a form of signalling which uses a rapid string of in-band tones. It is used mainly in Europe, Asia, Australia and New Zealand.

This sequence of tones usually consists of 5 separate tone frequencies, each one denoting a hexadecimal number. Numbers 0-9 are used as digits and numbers A-F are used for exreas such as repeat or group tones.

The repeat tone is used as when sending two consecutive tones, it is possible for the receiver to incorrectly decode them both as one digit. In order to avoid this, a repeat tone is substituted as the second digit. In this example, 'E' is the repeat tone and the code which is to be sent is 12344.

When sending, the second '4' is replaced with 'E' and 1234E is sent. At the receiver, the code is converted back to its original value of 12344. If 44444 needed to be conveyed, then 4E4E4 would be sent.

Maximum information transfer rate is 90 bits per second.

Very few scanners are able to decode SelCall although being as the are in-band, you can use just about any scanner to decode them via your PC with an application such as WinTone.

Download WinTone (1.5MB)

The different standard duration and frequency values were devised by international committes and sometimes amended by users or manufacturers. There are many standards and variations thereof.

Most radios allow arbitrary modification when programed. Dispite the huge array, you may often find radio systems in use which do not truly adhere to any normal of the normal standards.

Variables are not only the tone frequencies themselves, but also tone duration and time between the tones.

One of the great things about 'standards' is there are so many to choose between.

Frequencies shown in Hertz, times shown in Milliseconds.

The following tabe was taken from Wikipedia. Some discrepancies are apparent.

CCIR - Comite Consultatif International de Radio

EEA - Electronic Engineering Association, UK

Zuverein der Electronisches Industrie

Zentralverband der Electrotechnischen Industrie, West Germany

Originally designed to operate on 20kHz bandwidth systems so when used with todays 12.5kHz bandwidth systems, problems can occur with the highest tone which is 2800kHz.

For this reason, Depressed ZVEI was introduced which used 825Hz instead for the B tone.

DZVEI - Depressed ZVEI

DDZVEI - Double Depressed ZVEI

NATEL - Scandinavian National Telephone

They were generated using a Schlumberger SI 4923 Radio Code Analyser.

These files should decode in Wintone

Standard	Message	Tone Duration (ms)	Description	File
EEA	12345	40	Typical length
EEA	12345	120	Slower than usual
EEA	54321	120	Slower than usual
EEA	1234567890ABCDE	120	All tones
ZVEI 1	12345	120	Slower than usual
ZVEI 1	1234567890ABCDE	120	All tones
ZVEI 2	1234567890ABCDE	120	All tones