MDC-1200

Lore & Background

MDC-1200 was developed by Motorola as part of its Motorola Data Communications (MDC) family, which also includes the slower MDC-600 variant. The system uses AFSK to encode data as bursts of tones at 1,200 Hz and 1,800 Hz, sent over the voice channel. It supports a range of programmable features, including unit ID, status buttons, emergency button, selective inhibit, radio check, and selective calling. These features are typically found in high-end analog FM commercial and public safety radios made by Motorola and other manufacturers. At least two other companies produce compatible base station decoders.

Motorola radios with MDC options can be programmed to filter out data bursts from receive audio, replacing them with a short chirp. A general option enables or disables acknowledgment (ack) data packets, which confirm receipt of a selective call or status message. The ack packet takes roughly the same air time as the original call, doubling total air time on busy channels. Unit ID can be sent as leading or trailing a voice message, with leading IDs including a header tone and a programmable delay to accommodate CTCSS decoders and voting comparators. The standard Motorola encoder-decoder displays the most recent four-digit push-to-talk ID and can connect to a printer to log IDs and times.

Reader's Guide

MDC-1200's significance lies in its widespread adoption in public safety and commercial radio systems, particularly in environments where reliable unit identification and status reporting are critical. The system's unit ID feature allows dispatchers to see which radio is transmitting, and in computer-aided dispatch (CAD) environments, the four-digit ID can be translated to a local unit name, such as 'Downtown 6.' The emergency button sends the unit ID with an emergency flag, often repeated three times silently, and can be programmed to transmit on a specific channel to avoid interrupting primary dispatch. Status buttons reduce dispatcher workload by automatically logging predefined status changes, such as 'available' or 'meal break,' even when the dispatcher is on the telephone. Selective inhibit allows a stolen or unauthorized radio to be disabled remotely, sometimes called 'stunning.' Radio check and selective calling further enhance system control. During the patent period, Motorola charged heavy licensing fees, creating a lock-in that restricted many agencies to Motorola radios. Third-party manufacturers such as Midian Electronics, Control Signal Corporation, and Cimarron Technologies produce compatible encoder/decoder modules and dispatch display units.

Did You Know?

• Emergency messages are sent silently three times by default to increase the chance of reception.
• Selective inhibit is sometimes referred to as 'stunning' or 'radiokill.'