4 ms·

I'm working in a project for my local fire station to receive GPS data via VHF radio (widely used by emergency services in my country). We are trying with DTMF,

by emi420 7y ago

I'm working in a project for my local fire station to receive GPS data via VHF radio (widely used by emergency services in my country). We are trying with DTMF, this seems interesting.

paulie_a 7y ago
Don't they already do this? I hear them all the time on my scanner? Hell they use a four digit unencrypted code to activate the emergency sirens.
- copperx 7y ago
  I thought that fire trucks had a switch to activate the sirens by the drivers; I had no idea they were activated remotely by radio.
  - paulie_a 7y ago
    I was referring to the standalone towers in the Midwest. Maybe elsewhere. When I was a kid i would wake up on Saturdays at noon due to the siren. My dad also had a police scanner I could hear. One summer I put 1 and 1 together All you need is a dtmf decoder and a small transmitter to set the off those large sirens on high poles throughout that sprinkle the country in small towns and probably large cities
jrockway 7y ago
There is a lot of prior art here, the most relevant of which is probably APRS: https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_Sys... Newer digital modes do much better than this older AFSK system, but FSK does work pretty well. Some newer things to look into: https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) FT8: https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software) https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software) The more interesting modes (WSPR, FT8) are designed for high-loss channels, so have a lot of error correction. For example, I can use 5W of power, indoors, to communicate across the country with it. For high-bandwidth VHF channels, it doesn't matter what you use really. The goal would be to find something that already exists and is easy to integrate, and there are a lot of options.

by emi420 7y ago

I'm working in a project for my local fire station to receive GPS data via VHF radio (widely used by emergency services in my country). We are trying with DTMF, this seems interesting.

paulie_a 7y ago

Don't they already do this? I hear them all the time on my scanner? Hell they use a four digit unencrypted code to activate the emergency sirens.

copperx 7y ago
I thought that fire trucks had a switch to activate the sirens by the drivers; I had no idea they were activated remotely by radio.
- paulie_a 7y ago
  I was referring to the standalone towers in the Midwest. Maybe elsewhere. When I was a kid i would wake up on Saturdays at noon due to the siren. My dad also had a police scanner I could hear. One summer I put 1 and 1 together All you need is a dtmf decoder and a small transmitter to set the off those large sirens on high poles throughout that sprinkle the country in small towns and probably large cities

jrockway 7y ago

There is a lot of prior art here, the most relevant of which is probably APRS: https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_Sys... Newer digital modes do much better than this older AFSK system, but FSK does work pretty well. Some newer things to look into: https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) FT8: https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software) https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software) The more interesting modes (WSPR, FT8) are designed for high-loss channels, so have a lot of error correction. For example, I can use 5W of power, indoors, to communicate across the country with it. For high-bandwidth VHF channels, it doesn't matter what you use really. The goal would be to find something that already exists and is easy to integrate, and there are a lot of options.