figuring out frequencies and talk groups

[hockey4370]

hey guys i live in rhode island and i am confused as too figure out what talk groups go with which frequencies. i was looking at this http://www.radioreference.com/apps/db/?sid=4275 . i was specifically looking at Providence County - Providence City Fire Talkgroups. i am assuming that the DEC is the talk group but i dont know the frequency it belongs to.. any help would be greatly appreciated

 

[RoninJoliet]

In todays trunking scanners you set up the "Trunk System with what type it is, then enter the red and blue freqys which are the Control Channels that run the system and provide ALL the TG's....No one TG belongs to a certain channel, the control channel picks the freqy that compliments the TG....Your PD and FD have certain TG's that belong to each sevice but the freqys belong to all .....

 

[wyomingmedic]

Hello Hockey!!!

Scanning today's systems is a little daunting to wrap your head around if you are not used to technology. You may know some (or all) of this already, but let me write it out as a whole picture.

Modern systems that use talk groups (TGs) are digital systems. Just like a cell phone, the voice is converted to a digital format, to be sent over the air. It is then "picked up" at the receiving end and converted back into understandable language (hopefully LOL). But it also send out digital information that we cannot hear to the other radios who are listening. It tells them how to keep track of the conversation and where to go next.

The 2nd thing these systems do is "trunk". For example, your local digital system may have 10 frequencies that it can transmit and receive on. In a conventional repeater setup, this would allow only 10 agencies to have a channel.

With a trunking system, many dozens of agencies can use it. Because of the idea that not all agencies are going to be talking at the same time, the system can take the digital channel IDs (TGs) and assign them the next available frequency to talk on. Within the space of a normal conversation, the system may actually change frequency 4 or 5 times, but since all of the radios have the same TG, they will follow the conversation. The idea here is that you minimize silence on the frequencies, which is just a waste of the frequency. You can get a LOT more use out of several frequencies than we ever could before.

The problem can happen when everybody tries to talk at the same time. Then the user may get a busy signal similar to a telephone saying "try again later". But if the system designers have built the system correctly, it should handle all of the peak traffic and not lock anybody out.

So what does this mean to us scannists? Well, we need a scanner capable of following digital traffic. The scanners that follow current systems follow the TG associated with an agency, instead of the frequency (because there is no ONE frequency assigned to any agency).

Hope that helps,

WM

 

[ka3jjz]

If you want some detailed explanations as to how trunking works, this article from our wiki has lots of information...(anything in blue is a link)

Just look at the stuff in the overview section - UPMan's excellent intro article is linked there, and note that it's a PDF...

Trunked Radio Systems - The RadioReference Wiki

73 Mike

 

[hockey4370]

thanks for all the help guys. this new digital system came out of no where for us and i couldn't really grasp it. it seems like a great improvement over the uhf/vhf that most of are state has.