Another d**n newbie question....

[davenkaryn]

Afternoon all, I have been reading everything I can get my hands on regarding digital trunking, but it's still not too clear to me. To some extent I understand the concept of trunking, but I don't know how to get it to work in my BC296D. Unfortunately, the instruction manual is about as helpful as, well, nothing. I used the standard frequency "Search" function on my scanner to locate a dozen or so 800 MHz frequencies for Howard Co.; just enough to keep me entertained. But, when I look in the RR Database for Ho Co it looks like I'm missing a lot of the good stuff by not listening to the talk groups. I guess it's throwing me off because I am old-school and only recognize frequencies in the decimal-point format, such as 866.375 and such. If I understand trunking correctly, within this specific frequency there are sub-frequencies that are controlled by a central computer. That computer receives a header from the incoming packet which identifies the transmitting radio. The computer then assigns that transmission to a specific channel within the assigned frequency. Does this sound right? I realize that over time and with extensive studying I will eventually understand all this stuff. But in the meantime, for my listening enjoyment, can someone post a quick & dirty method for assigning talk groups on my BC296D? By the way, it has the APCO-25 card in it. I got it from www.usascan.com (not endorsing the sight, just saying). Thank you in advance to my fellow Marylanders for helping out this newbie. --Dave.

 

[crayon]

davenkaryn,

Welcome to the group!

I cannot comment on how to setup your BC296D since I do not own one personally, but I'll take a stab at Trunking 101 concepts for ya.

If I understand trunking correctly, within this specific frequency there are sub-frequencies that are controlled by a central computer. That computer receives a header from the incoming packet which identifies the transmitting radio. The computer then assigns that transmission to a specific channel within the assigned frequency. Does this sound right?

ummm .. in a word - sorta. There is not any sub-frequencies and we dont really use the word channels in the context of a trunked system. Some departments might tell the users they can use a channel A or channel B .. but this is really a label for a talkgroup.

Usually, a trunked system will contain a group of frequencies. Lets say five frequencies make up our example group. One of these frequencies will be transmitting the control channel all the times. The information contained in the control channel is what is pivotal to understanding trunking. But first we need to talk about talkgroups. So here goes ..

In the past it was one or two frequencies per department. One for Police, one for fire, one for the dog catcher, and so forth. On a trunked system department get assigned a talkgroup. The beauty of this is you can have as many talkgroups as you want without needing to acquire additional frequencies!

With that being said, our example control channel is spewing out information about which talkgroup(s) are now currently active on which frequency.

So you got Joe Officer sitting in his car and it just so happens that his patrol group has a talkgroup ID of 12345. Even though his radio is not active, it is listening to the ever present control channel for talkgroup/frequency assignments. Once the control channel assigns his talkgroup ID a frequency (because someone within the 12345 talkgroup keyed up), his radio will automatically tune to the assigned frequency (one of the four that is not in use) and break squelch.

This is a very effeicent way of radio communication for large organisations, because the law averages is that not everyone is going to be talking all at the same time. Dynamically allocating frequencies from a pool gives radio access to more people on less frequencies.

Hope that helps ya out ..

 

[Llwellyn]

Without going into the theory of it, think of a trunked controller being like a "router" for radio traffic. Talkgroups are not sub-frequencies; they are logical, rather than physical, allocations given by the controller. It uses computer language and subaudible tones to route the traffic and keep it separated.

For programming the scanner, the easiest method is to use some form of scanning software to program it in... if that's not feasible, then it's easiest to set up the system on control channel only mode.

You have to specify this through the menus and program the frequency through the menu, not just into the bank like a regular frequency. You also have to enable control channel only mode, which is another menu option.

I'd take you through the exact steps but I'm sure someone else can post it quicker than I can, as my scanner is at home and I'm at work until 7.

 

[davenkaryn]

Thanks for the explanation. That certainly makes sense. So, the talk group ID is a sub-component of a frequency? Is it an N:1 ratio; in other words, multiple talk groups for 1 frequency?
I'm using the Uniden software that came with the scanner. So where do the talk-group IDs go? It's pretty straight-forward for programming standard frequencies, but I'm not sure where the talk group IDs would go. If anyone has a .txt or some other type of file for Howard County frequencies, that'd be greatly appreciated.
I've really enjoyed listening to everything that goes on in this crazy county. Everyday someone does something that makes me scratch my head. I always thought cops in Ho Co would be bored out of their skulls, but now I realize they're too busy responding to residential and business false alarms.
Thanks again ya'll. --Dave

 

[Llwellyn]

The talkgroups are a component more so of the trunked system than of the frequency; there is no set ratio. Any given talkgroup could appear on any of the allocated frequencies at any given time. They are just simply a way to separate traffic from other traffic.

The control computer just monitors each of its available frequencies to find the ones that are not in use. Howard County I believe uses 16 frequencies... the chances of 16 users talking at once is practically nil except in the case of an extreme disaster. So the controller will assign talkgroups the next available open frequency when traffic is being passed.

PD 1 presses his PTT button to talk to dispatch to call 10-8. His is the first transmission for a while, so let's say he gets the first frequency. Then FD 1 calls the station on their admin talkgroup to tell them to start cooking dinner. He gets the next frequency, #2. Meanwhile, PD 1 has concluded talking for the moment on his talkgroup, but then dispatch calls him back a few seconds later; in the meantime, however, the dog catcher calls in that he's going on break, and is assigned frequency #1 since PD 1 was not actively transmitting or receiving. When PD 1 keys up again, he'll get frequency #3 but still be talking only to his dispatcher and other PD employees... so the same talkgroup will be on multiple frequencies over a given period of time. The talkgroups are what separate the traffic apart from all the other traffic and ensure that the units are talking to the right dispatch and only receiving traffic that is relevant to them. All of this is being conducted by the controller over the control channel frequency.

As far as working with the E-scanner software, I didn't use it to program my scanner. It's a horrible program as far as the interface is concerned so I'm not surprised you can't find what you're looking for (I couldn't and gave up on it). I used the demo version of Trunk*Star 785D for my programming, and next paycheck I'll probably buy the full version. ARC250 is another good one. Do a search in this forum and you'll find an earlier post where I linked these two programs. I'm at work still so I don't have access to my bookmarks. Either one will use your existing interface cable, nothing additional is needed and both of them are MUCH easier to use. You'll also likely be able to find an ARC250 file for Howard County.

 

[davenkaryn]

Thanks Llwellyn!

I downloaded the demo version of ARC250 and it is awesome! This is definately a lot easier than that junk that Uniden wrote. Once I got ARC250 downloaded & installed I googled ARC250 and Howard County and found a link to Capitol Hill Monitors Scanner Radio Home Page. That's where I found plenty of .mem files to keep me occupied for a few more weeks. Thanks for your help and as I learn more I'll try my best to pass along my knowledge to other newbies.

Thanks again, and Go Orioles! 8) I love New York; it's the Yankees I hate!

--Dave

 

[emtLarmy15]

The most simple description of a trunked radio system that I have ever heard is as follows:

Imagine you are in a bank (where you get money..)
You and everyone else stand in a line. Imagine every person in the line is a "talkgroup", The tellers are the "frequencies". As a talkgroup needs to talk it goes to the next available frequency. When its done talking it goes back into line. And the frequency is freed up for the next talkgroup in line to follow.



Then on top of all that.....
this is just for kicks...
You throw in things like Opensky which can carry 4 voice conversations on one frequency at one time
Priority talkgroups.... such as PD probably has priority over animal control...

Trunked systems do SOOO much.

Chris

 

[davenkaryn]

Great post and excellent description! Thanks! I got a bunch of talk groups loaded into my scanner last night and I think I finally understand how it works. I could see the conversations taking place on different frequencies which were very close together. The other way I could follow them was based on the 5 digit M- ID, which I assume was the talk group ID. Police converstions were on IDs like 45616 and 42070 (I think those numbers are right, or at least close). Thank God for the ARC250 software because I don't think I could've programmed that info on my own. Thanks again to everyone for their assistance and explanations.

--Dave

 

[TinEar]

Dave, you're getting into the red meat area now and you'll soon see how simple the system is - once it's all programmed into your scanner. Talkgroups 47120 (North Dispatch) and 47152 (South Dispatch) will quickly become prime listening for you. If you download one of those memory files from Capitol Hill Monitors you'll have all the talkgroups programmed too and they'll be identified with their ID tags so you'll know precisely what you're monitoring. I have two files posted there although small changes to Howard County have taken place since I posted them. Use the data base at this site (top of this page marked RR Database) to keep up with changes in identities or new recoveries. Using the ARC250 program makes life much easier as you're finding out.

 

[bear105]

If you download one of those memory files from Capitol Hill Monitors you'll have all the talkgroups programmed too and they'll be identified with their ID tags so you'll know precisely what you're monitoring.

Yup...a great place to start for files but I noticed lots more in some of the Yahoo Groups for specific programs. For ARC250 there is the arc250785 group. MEM files are arranged by state for the whole country. DC, MD and VA have several files...

 

[davenkaryn]

Another favor....Could someone post a link to a good list of 10 codes for Howard County?

Thanks all,
--Dave

 

[n3bxv]

Click on Bear105's Profile and follow the link to his homepage, he has most Maryland Counties' freqs and codes detailed..

Chuck