Technical informations - Systems

Versione radioamatoriale del sistema CCIR X25 ma con campi di indirizzamento estesi. La trasmissione Ŕ costituita da pacchetti di dati sincroni inviati alla velocitÓ di 300 baud in HF e a 1200, 4800, 9600 baud in VHF. Ogni FRAME o 'pacchetto' Ŕ costituito da : una sequenza sincronizzata, un segnale di inizio, un campo di indirizzo, un pacchetto effettivo di dati fino a 256 caratteri in modo ASCII, un'informazione CRC, e un segnale di fine.

A mode used to allow data communications between PCs and dumb terminals. This system is typically used by radio amateurs, and to a lesser degree, United Nations organizations. Incompatible versions also exist and are in use by quasi-governmental organizations such as ICRC, UNHCR or IFRB. Typically the AX.25 protocol incorporates a modified CRC. On HF there are a few items to note. Typically 300 bd on SW. Data is arranged in packets of up to 256 bytes of 8 bit ASCII data. Each packet contains a 1 byte start flag, 3 byte address field, 1 byte control field, 0-256 bytes of data, 2 byte CRC and finally a 1 byte end flag. Packets are transmitted with no fixed timing. See the latest specification published by the American Radio Relay League (ARRL) for complete details on this system. There is also some 1200 baud PSK work done in the 10 meter ham band.