Question about Alabama Interoperable Radio System (AIRS)

[threeofnine]

Several agencies across the state use AIRS Alabama Interoperable Radio System (AIRS) Trunking System, Varies, Alabama. The system is composed of several towers spread out across the state. I am slightly confused as to how the system works. When choosing towers I was recommended to only choose the towers closest to me. Do all the towers act like repeaters or relays, and if so, would this mean that one could listen to an agency 200 miles away or does range from the source still matter?

 

[RaleighGuy]

Several agencies across the state use AIRS Alabama Interoperable Radio System (AIRS) Trunking System, Varies, Alabama. The system is composed of several towers spread out across the state. I am slightly confused as to how the system works. When choosing towers I was recommended to only choose the towers closest to me. Do all the towers act like repeaters or relays, and if so, would this mean that one could listen to an agency 200 miles away or does range from the source still matter?

Each repeater works for a specific area of coverage, as a unit travels across the state it moves from repeater to repeater, it doesn't mean you can hear traffic on all the repeaters from all areas. That said there are exceptions, if an out of area unit is able to affiliate with a local tower you and calls back to his home TG, then you will be able to hear the communications from that TG on your local tower.

 

[TomServo]

I find the way trunked radio systems work pretty fascinating and RaleighGuy's explanation is a good one.

What you'll be able to hear really seems to depend on how much coverage the agency needs. If you're willing to share where you're located, someone in that area might be able to tell you what you could hear.

As an example of how quirky it can be, I'm in central Baldwin County, and can't hear some comms in Orange Beach and Gulf Shores despite both being less than a 14 mile drive from my listening post. The sites in Orange Beach, Gulf Shores and Fort Morgan just don't come in where I am. But at the same time I regularly hear Medstar EMS calls in Escambia County, which is like a 1.5 hour drive away, all off the Seminole tower.

In the summer, it's not unusual for the local towers to start playing some police comms from well outside the area, due to officers bringing their radios with them on beach vacations, ha ha. And if Life Flight from central AL is in the air and down this way I can hear some of their stuff from anywhere from Birmingham to Atlanta or Columbus, which is pretty neat.

 

[threeofnine]

If you're willing to share where you're located, someone in that area might be able to tell you what you could hear.

I'm in north Jefferson County, almost right between the Graysville and Warrior towers. Speaking of that, is it possible to monitor all traffic going through an individual site, for example the Warrior site?

 

[radiogod_2103]

NO
Them sites are called stand alone towers. They only broadcast traffic that a radio connects to. example would be like warrior pd, warrior fire, kimberly fire, morris fire, and prob the sheriff's department. i am not able to hear them 2 sites. but based off a knowledge of the warrior area i am pretty sure thats who you would prob hear. I know for a fact you will not hear birmingham fire or hoover pd/fd unless they are within range of that tower. If you want to hear everything in jefferson county you would need to monitor the main simulcast site and i see from reading your other posts you have a sds 100 . So you should not have any issues with the main simulcast site

 

[morganAL]

RaleighGuy is spot on with his explanation. Yes, there are some statewide talkgroups but most of them require a radio to be affiliated to that talkgroup in order for a site to transmit any traffic on it. There's no benefit in tying up limited site resources to transmit something that no one is listening to. Explaining that to LEOs was always a pain. They wanted to scan and hear EVERYRHING and didn't care about technical limitations. It was always the same answer.. "we used to hear everything on the old radios". Simulcast sites vs the non-simulcast interconnected sites has an advantage in that respect but there are other factors that can preclude the use of simulcast; cost and terrain being the biggest 2.

Retired AIRS sys admin.