Many public safety pagers and control systems use audio tones to activate. The most common type are two tones that are sent in sequence. Hence it’s names, Two-Tone Paging or Two-Tone Sequential.
A valid two-tone page is comprised of four elements:
If all these items match what the decoder is expecting, it processes the signal and takes action such as beeping, engaging relays, starting times, etc.
If any of these items are incorrect, the page is ignored, and the decoder waits to analyze the next paging signal.
We also take this normal structure and extend it much, much further with non-predictive, Free Format Control.
Listen to an actual page. 788.5 Hz / 600.9 Hz with a 1 second / 3 second timing. This is the Motorola Quick Call 2, Reed Group 2, Code 61. You may have noticed this two-tone page uses the same tones as the page above it, but the tones are reversed. This is quite acceptable. The decoder is watching for the correct tones and the correct tone timing so it treats both the first audio page and the second audio page as completely different events.
These pages are all sent over the same radio channel for every radio, pager and remote decoder in the area to hear, and decide if the signal is intended for them to initiate some action.
Consider a paging signal that has the following characteristics …
In the communications industry, this would be referred to 321.7 / 339.6 at 1 second / 3 second
When this signal is transmitted over the two-way radio, any pagers or control equipment such as sirens, pumps, etc. would be activated if this paged matched what they were looking for.
If any part of the page did not match the decoder in the field, then the radio decoder or pager would ignore the page and would not activate.
If the tone frequencies were both correct, but the decoder required 3 seconds of the first tone, then it would ignore the signal when it only received 1 second of the first tone.
Single-Tone paging is many times referred to as “All-Call” Paging. Where Two-tone pages are normally employed to contact an individual, or a group of decoders or pagers, the All-Call paging signals are normally used to activate all groups. An Single-tone page is only one tone, and it lasts at least double the time of a normal Two-tone page. A common Motorola format has an All-Call tone length of eight seconds.
Other Signaling Codes