DMR Slots, color codes and Talkgroup interaction

[wbloss]

I was in Columbia, MO recently with my TRX-2 and peeked at the University of Missouri DMR TRBO system.

This is my first foray into DMR trunking and I am needing to understand the relationship of slots, color codes, talk groups and frequency assignment.

In this system, a slot/color combination apparently gets you to a specific frequency in the list of frequencies on the system.

So far I have determined the following slots and color codes show up only on the specific frequency:
S1c2--- 859.2125
S1c3--- 858.2125
S1c5--- 856.2125
S1c7--- 855.2125
S2c1--- 860.2125
S2c3--- 858.2125
s2c5 --- 856.2125
S2c7--- 855.2125

Is this normally how DMRs work? Seems quite different from the process of P25 NACs and trying to make an analogy is difficult.
Any help?

Wally

 

[RayAir]

Think of a color code as a PL tone.

There are many different flavors of DMR (simplex, conventional repeater, IP Site Connect, Capacity Plus, Connect Plus, Hytera XPT, Hytera Pseudo Trunk,etc).

Example of a single frequency conventional repeater set up:

461.9625 Color Code 1
Time slot: 1 Talk Group: 1 Security Dispatch
Time slot: 2 Talk Group: 2 Maintenance

The repeater sync's the time slots so two users can use a single 12.5KHz frequency at the same time.

For a better understanding of DMR, I'd search for MotoTRBO System Planner and download it. It will explain the ins and outs. There's also a Connect Plus System Planner and Hytera has their own planner also.

They'll give you a better idea of how the systems you're trying to scan operate.

 

[nd5y]

A DMR repeater has one color code and two time slots.
In a DMR trunked system the talkgroups are assinged to a voice channel repeater and time slot. As far as I know the color code is always the same for a particular repeater.

DMR Color code is about the same as P25 NAC.
Normally P25 trunked systems use the same NAC on all repeaters but they don't have to.
Normally P25 conventional repeaters use talkgroup ID 1 but they don't have to.

 

[Project25_MASTR]

Looks like you spied a trunk system and guessing from the fact it's 800 MHZ (Tait is the only other 800 MHz DMR manufacturer in the US currently thats in common usage) I'd guess a Capacity Plus (Motorola pseudo trunking) system.




Sent from my iPhone using Tapatalk

 

[K845rp]

W5, I saw the 800Mhz too and thought thats odd -- never seen that in my area --
I suspect the more main line use is going to be the cheaper Radio (MD380/390) Freq. as the one thing I think these inexpensive radios have done is brought many more operators (back) on the airwaves (assuming they are comfortable and able to learn new tech, which many of my older friends, like computers, think (THINK) they don't need it or want it -- when I explain the advantages they go "Hmm"

Murph

 

[YehudaEMT]

How many talk group number are there like for example 1 to ?

 

[KevinC]

How many talk group number are there like for example 1 to ?

1 to 16776415 .

 

[YehudaEMT]

So there is no way to figure out someones talk group?

 

[n5ims]

So there is no way to figure out someones talk group?

Most scanners (not talking commercial radios here, but typical scanners such as those from Whistler and Uniden) that have the necessary firmware updates to handle DMR can be programmed for "a wildcard talkgroup" that will decode any talkgroup on frequency and display the talkgroup number. They will similarly handle "wildcard color codes" and will decode any color code and display what one was being used.

Using those features, you're in a good place to figure out the talkgroup information. That's the "easy" part. The hard part is listening to that talkgroup over time to figure out based on the traffic who may use it and what it's used for. For example, if you hear lots of traffic on a talkgroup dispatching tow trucks to various locations, you can be pretty sure that talkgroup is used to dispatch tow trucks.

Further listening may allow you to catch which company's trucks are being dispatched, perhaps something like "Truck 7, pick up a blue Toyota at the city PD's investigation lot and deliver it to the impound area for the Jones Wrecker Service main secure parking area. When you get here, hand me the paperwork and let me know which space you parked it in.". You may even get lucky and have them dispatch to a location just down the street and you can read "Jones Wrecker Service" on the tow truck as it passes by.

I DO NOT recommend driving to a dispatched location to help do any of this identification. First off, it gives scanner users a bad name to show up at a scene and make it more difficult for everyone attempting to work that scene. Second, you don't know what's going on at that scene and you may get trapped into something dangerous or at best be stuck there while they attempt to clear the affected area. Also, they may dispatch from multiple companies to help clear the scene so you still won't know which company it was.

 

[YehudaEMT]

Thank you very much i know the company name just when i searched for the frequency the color code showed up and the talk group had a * as well as the zlot number so if the scanner can show the talk group i should be good to go just can you throw a scsner model out I'll look into it