The easiest way to find trunked systems in the United States is the radioreference website alternatively you can google or if you are really persistent scan the frequencies. The access to systems like these to perform research is very limited by government bodies, regulations and getting hold of the devices to test.
For example if we look at the recordings below from the SF Fire Department: An example would be one of the San Francisco groups for the police is called Dispatch Mobiles Southern B Tenderloin J Districts, which covers all police working in these areas.Īnnouncement Groups (or sometimes just Groups) are a larger category that hold various TGs that might be relevant to a certain department. These talk groups are typically things like a group of people working in the same area where sharing all calls is relevant. Radios on trunked systems are divided up into what is called “Talk Groups” (TGs), which is simple a group of radios that all “talk” to each other. The control channel tells radios what frequencies they should tune to to listen to ongoing calls, where they should tune to make calls and other information that is needed for day to day usage. These control channels are usually digital broadcasts that radios “listen” to while not in use. The majority of a trunked networks are handled by what is called a control channel, there are always one or more of these (usually 2 primary and 2 backup channels). If we didn’t have these systems people would be a mess trying to find each other on the same channels (frequencies) and talking over each other!
A trunking system ensures different calls (talkin’ on the walkies’) can be made at the same time without any user interaction to change channels, unsquelch or perform any manual tasks to make and receive calls. The essential gist of trunked networking is that it is a way to share a small amount of communications paths (bandwidth) over a large number of devices. In San Francisco the system used is Smartnet.
Basically after having a look at some of the documentation this is the basic premise, and seems to fit for all trunked networks, from the older Motorola Smartnet systems to the newer P25 networks. We are gonna go through setting up trunk-recorder as well as uploading all the calls to OpenMHz so that we can listen to all these calls! The end product looks something like this:įirstly, I am not a radio person, so a lot of this is guess work and lies. This is because it is a trunked radio system, there is a control channel that radios follow to figure out what frequency to ‘talk’ on. The thrill of randomly clicking on every spike that comes up and being able to hear the audio is amazing! However it quickly becomes tedious as they keep popping up all over the place and you have to try and chase them down. Generally you will be able to find the range they are in and see some sort of waterfall that looks like this with your radio: Naturally this often extends to networks of people with radios (sometimes called portables?) such as Police, Fire, EMS, Security services and so on. One of the more common things to do with an RTLSDR (or any SDR for that matter) is to listen to what’s being transmitted. I am uploading all of San Francisco CERS ( Public Safety ), including Police/EMS/Sheriff/Citywide/gov/etc to Ĭovers the area in the pic attached. TLDR You can listen to all of the San Francisco CERS (Public Safety) Trunked system at , this guide will show you how you can do the same for it or another trunked system!