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.