data are sent in bursts over the radio system's voice channel. Motorola radios with MDC options have an option allowing the radio to filter out data bursts from the receive audio. Instead of hearing the AFSK data, the user hears a short chirp from the radio speaker each time a data burst occurs. (The user must turn on this feature in the radio's option programing settings). MDC signaling includes a number of features: unit ID, status buttons, emergency button, and selective calling. These features are programmable and could be used in any combination desired by the user. They are typically incorporated in high-end analog FM radios made by Motorola. In addition to Motorola, two other companies make compatible base station decoders for MDC-1200. Other in-band signaling Modat Modat, also written MODAT, is an obsolete Motorola data system using a sequence of seven audio tones similar to the five-tone-sequential Selcall format. Some systems still use Modat today. Modat is used for unit ID and emergency buttons, rather than for selective calling. In a typical installation, each radio in a system is assigned a unique seven-tone code. Each time the radio's push-to-talk button is pressed, the radio transmits the seven tone sequence at the beginning of the transmission. To prevent the user from talking while the tone sequence is broadcast, the seven-tone sequence is played over the two-way radio receiver's speaker. Modat tone sequences are described as either a six-digit or seven-character string. For example, a single Modat code could be described as either 698R124 or 6988124 (where the "R" tone indicated "repeat the last digit"). The data format coming from a Modat decoder is unclear. Modat features are programmable and could be used in any combination desired by the user. For example, some systems use only push-to-talk unit ID or only emergency button. Others may use both. One setting that is adjustable is the length of time from push-to-talk press until the tone sequence starts. This delays the start of the tone sequence to allows systems with long time constants in CTCSS decoders or voting comparators to open an audio path. In addition to Motorola, other companies make add-on encoders that can modify a different brand of radio to work with a Modat system. Modat unit ID systems are frequently heard from radios on Barbour television productions, such as the Cops television show, portraying southern California law enforcement agencies in the