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.