Two tone voice pagers are still the defacto standard for volunteer fire departments in this part of the world, so it isn't so obsolete. Some areas each department has their own radio frequency, and tones for the pagers may or may not overlap, other areas use a shared frequency for the county, with different departments having different tone pairs. The county to the North of me, when they do their weekly test, sends tones for almost 2 minutes before the dispatcher can put out the announcement. (4 seconds per pair, 50 something paging groups)

Tony Langdon <vk3jed@vkradio.com> wrote:

On 27/05/13 3:34 AM, Bear Albrecht wrote:
On 5/26/13 11:10 AM, Brad NK8J wrote:
Most Fire Stations and ambulances require DTMF Tones to tell them which
station is being sent out to where.  
Well, not exactly. The system here is "two-tone" which has one single tone transmitted for a couple of seconds and then another single tone for a couple of seconds. Precise timing I can look up on Tuesday if needed. Google "two tone paging" for some of the angles. http://www.batlabs.com/qcii.html has some of the info although it doesn't cover what we use, nor several other variants.
We used to use that here in the late 1980s. I was toying with the idea of building a decoder (before software methods were practical) when we had the system installed. I got good at picking the tones by ear in the end, could tell ours from others in use. Those days are long gone, as we now use a statewide single frequency POCSAG network, independent of the voice channels for emergency callouts.
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