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- In a conventional, analog two-way radio system, a standard radio has noise squelch or carrier squelch, which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel (co-channel users), selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—individual calling and group calling. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios. Selective calling is akin to the use of a lock on a door. A radio with carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct "key", in this case a specific digital code. Selective calling systems can overlap; a radio may have (group call) and DTMF individual calling. Selective calling prevents the user from hearing others on a shared channel. It does not eliminate interference from co-channel users (other users on the same radio channel). If two users try to talk at the same time, the signal will be affected by the other party using the channel. Some selective calling systems experience falsing. In other words, the decoder activates when a valid signal is not present. Falsing may come from a maintenance problem or poor engineering. (en)
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- leading push-to-talk ID with data muting. (en)
- leading push-to-talk ID without data muting. (en)
- Sound of a two-tone sequential dial up paging terminal. (en)
- Example of a CCIR-format call. (en)
- Example of pick up and delivery truck radio traffic using Modat unit ID. (en)
- Two Quik-Call I sequences. (en)
- Single tone or tone burst selective calling audio example. (en)
- Example of DTMF used as push-to-talk ID on a two-way radio system. (en)
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- TRucking leading PTT ID MDC1200 non-Motorola recvr.ogg (en)
- Trucking w leading PTT ID using MDC1200.ogg (en)
- CCIR 04221.ogg (en)
- CEGL DKNP Z.ogg (en)
- DTMF trucking push to talk ID example.ogg (en)
- Modat trucking example with ID 6988103.ogg (en)
- Simulated two tone sequential code 415.ogg (en)
- Trucking tone burst.ogg (en)
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- MDC-1200 sounds (en)
- DTMF P-T-T ID (en)
- MODAT push-to-talk ID (en)
- Quik-Call I (en)
- SelCall (en)
- Tone and voice paging example (en)
- Tone burst sound (en)
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- In a conventional, analog two-way radio system, a standard radio has noise squelch or carrier squelch, which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel (co-channel users), selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—individual calling and group calling. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios. (en)
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