Question about LTR?

[klown]

As I understand it our local law enforcemant and fire department use a LTR system. When I think of a trunking system I think of 5 or 6 different frequencies with the radio having the capability to skip to the one not in use. But when listening to my scanner I hear all of the organizations using only one frequency, with the exception of a scrambled frequency that gets used very seldom by the SO and is shared with the city water dept. Often times while I'm monitoring I will hear a dispatcher in the background talking to another officer. I have done a search on all the frequencies being used by our local government, but never here them on any other frequency. I have all the frequencies punched in on my scanner and you can hear them make a short transmission (not voice) which I've read is typical of a LTR system. I have also heard them say go to tac, when they do I search all the frequencies I have stored and can't hear anything, but when they say go to ch. 4, I know that means they are going to use the frequency in which they scramble on. Can someone shed some light on the subject. Thanks.

 

[vs1988]

I'm sure others here can explain it much better than I, but a trunked system is basically a computer controlled radio system. When a radio keys up, it sends subaudible data to the computer, which then assigns it a frequency and tunes all other radios on that talkgroup to that frequency. Moto, EDACS and LTR are all different forms of trunking, but the premise is the same. I believe LTR always sends out bursts of data to let the computer know that the radio is there, and there is no control channel.

 

[captclint]

Before I got an LTR capable scanner, I listened to an 11 Ch LTR system for 3 months. Most of the time, it appeared as if they never deviated from the home channel. Once I mapped the system, I found that 95% of the time, they really did use the home channel. The other 5% of the time was very brief in most cases, so you really wouldn't notice you were missing anything with a conventional scanner. Of course, the number of times a non-home channel is used is dependent on the peak traffic on the system at any given time. Yours may not have a lot of simultaneous traffic. As for your mystery channels, I also found several "hybrid" systems. By that I mean, one or more frequencies were being used under a different license (same licensee) at the same location, but often one or two were licensed ONLY at another location as much as 30 miles away. This is all in the FAQ:
http://wiki.radioreference.com/index.php/Mapping_an_LTR_System
, but it is less likely that a public service LTR would do these "tricks". Just food for thought.

 

[klown]

Also I did a search on the frequency that is used by the S.O. and water dept. (460.6750) and it does not show up on the uls database. Is there a reason for that?

 

[NeFire242]

If its a TAC (talk-around) freq it could be lower power (portables) or you won't be able to hear it because it's not through the repeater and good antenna so it would be a much weaker signal.

You may not have the LTR in it's logical channel number order (LCN) so you may not be following the system correctly.

 

[scanfan03]

If its a TAC (talk-around) freq it could be lower power (portables) or you won't be able to hear it because it's not through the repeater and good antenna so it would be a much weaker signal.

You may not have the LTR in it's logical channel number order (LCN) so you may not be following the system correctly.

I'm pretty sure he's using a conventional scanner.

 

[klown]

Iam using a conventional scanner and a vx-800 uhf transceiver. The thing that gets me is that they only use one frequency. You can hear the burst on the other frequencies within the system but they are never used. So there is no change I'll be able to decode there sub-audible tone with my vx-800.

 

[scanfan03]

Iam using a conventional scanner and a vx-800 uhf transceiver. The thing that gets me is that they only use one frequency. You can hear the burst on the other frequencies within the system but they are never used. So there is no change I'll be able to decode there sub-audible tone with my vx-800.

Everybody must be on the same home channel. For that one back channel, your going to have to do a search (It sounds to me like it is going to be simplex) in the UHF band.