Clarifying the Amateur Bell 202 Modem

Since its inception more than three decades ago, packet radio has seen several significant changes in technology and applications. Despite its age, the 1200 baud Bell 202 modulation used in some of the earliest packet systems still enjoys a wide user base in several of the major amateur packet networks. Oddly, despite being one of the longest-lived amateur packet modulations in use, the amateur radio community seems to have neglected to write a detailed specification document for this integral part of so many packet systems. This paper presents information gathered from network protocol specifications and amateur packet radio articles to assist other amateur radio operators implementing modems for this prototypical modulation.