DMR Question

[tommypickles]

I am new to scanning and receiving DMR.
I have been monitoring a local school system that has a one frequency DMR repeater.
I understand that the color code is similar to a NAC in a P-25 system.
I have received 3 talk group ID's, 1000, 2000, and 3000.
I have identified TG 1000 as the buses and 3000 as teachers at dismissal time.
My main question is the time slot.
The scanner has always displayed the color code (9) and one of the above TG's.
The thing that changes is the time slot. The TG's are showing as being in slot 1 and 2.
When I see a posting on radioreference it usually shows a CC # folowed by a TG # then by an SL #.
Do the TG's on a single frequency DMR repeater change time slots? No data such as GPS is being transmitted in the apposing slot, at least from what I can tell.
Thank you for your responses.

 

[hiegtx]

I am new to scanning and receiving DMR.
I have been monitoring a local school system that has a one frequency DMR repeater.
I understand that the color code is similar to a NAC in a P-25 system.
I have received 3 talk group ID's, 1000, 2000, and 3000.
I have identified TG 1000 as the buses and 3000 as teachers at dismissal time.
My main question is the time slot.
The scanner has always displayed the color code (9) and one of the above TG's.
The thing that changes is the time slot. The TG's are showing as being in slot 1 and 2.
When I see a posting on radioreference it usually shows a CC # folowed by a TG # then by an SL #.
Do the TG's on a single frequency DMR repeater change time slots? No data such as GPS is being transmitted in the apposing slot, at least from what I can tell.
Thank you for your responses.

That's going to vary by system. In some systems, a specific talkgroup ID will always use the same slot. But in other systems, such as what it appears you are seeing, the TGID could be in either slot. Unless I can verify, positively, that a given talkgroup will only ever use one specific slot, then I do not assing a slot in OFT systems. The scanner will then receive the TGID no matter which slot is used for the transmission.

 

[tommypickles]

Steve,
Thank you for the information.
Always something to learn in this hobby.

 

[werinshades]

That's going to vary by system. In some systems, a specific talkgroup ID will always use the same slot. But in other systems, such as what it appears you are seeing, the TGID could be in either slot. Unless I can verify, positively, that a given talkgroup will only ever use one specific slot, then I do not assing a slot in OFT systems. The scanner will then receive the TGID no matter which slot is used for the transmission.

I have also found the same thing on DMR OFT systems. When I assign a talk group a slot, put it in ID search, their are times it will appear as a new talk group displayed. Slot set to Any and set to ID search is the best option.

The only method that would require assigning a slot number is if the same talk group is used for separate users. I have a couple of those. Then you assign it with the Slot number (Ex. Security TGID 169/Slot 1...Maintenance TGID 169/Slot 2).

 

[IAmSixNine]

This might help.
Go to your main menu, Search For... Select the frequency band that your monitoring, then hold on the frequency your currently listening to. If its conventional it will show DMR, if its trunking it will show Cap or Con or i think T3.
Because you are seeing the same TG using different slots its possible its a cap plus single frequency system or one of those hytera psudo trunking systems.

 

[WA0CBW]

I don't know how scanners handle time slots but in the commercial DMR world the only way a talk group shows up on two time slots is that it is programed twice, once on each time slot.......like werinshades said. In DMR three things are required for a talk group, the ID, time slot and color code.
bb

 

[IAmSixNine]

OP said he was new to DMR, and is seeing the same TG ID appear in both time slots so its possible he has stumbled upon a 1 channel cap plus system or a hytera psudo trunking system.
By going into frequency search mode, and him holding on the frequency, this should help him identify it is a true DMR concentional or if its cap plus or other trunking.

 

[DaveNF2G]

When using Uniden's OFT option, you can set the slot on each TG to Any and you don't have to be concerned with which one is actually used. If you configure the channel as DMR Conventional, then you need the slot numbers to be correct for each TG.

 

[werinshades]

OP said he was new to DMR, and is seeing the same TG ID appear in both time slots so its possible he has stumbled upon a 1 channel cap plus system or a hytera psudo trunking system.

Their are a couple DMR OFT systems around me who assign one talk group ID to each slot. If he listens long enough, the usage will be determined.

During a conventional search, if DMR is showing in the display, you're receiving a One Frequency DMR system. CAP/CON/IDAS is a trunking system.

 

[werinshades]

Their are a couple DMR OFT systems around me who assign one talk group ID to each slot. If he listens long enough, the usage will be determined.

During a conventional search, if DMR is showing in the display, you're receiving a One Frequency DMR system. CAP/CON/IDAS is a trunking system.

Didn't have time to edit:

I have a couple of systems that assign Duplicate TGID's to each slot per frequency.

 

[IAmSixNine]

Assigning duplicate TG ID to each time slot is still a DMR Conventional set up. Uniden likes to muddy the waters (my opinion) by calling it a OFT even though its not actually trunking. There is no site controller. Its a conventional DMR channel that is using different TG with different time slots. The reason they like to call it OFT is so you can program in the different TG in different time slots and enable or disable them.
True trunking would be Cap plus, Con Plus or T3. The only trunking i am aware of with out a site controller is Hytera pseudo trunking. That will use the same TG but it can use either time slot. That is controlled by the hytera repeater and is proprietary to hyetra and is an option / feature they offer. But not many of them around that i am aware of. @werinshades im not arguing or disagreeing with you, just clarifying a bit. There are many ham repeaters around me who use different TG on different time slots. You do program them as OFT in a uniden scanner but its a DMR conventional channel as no actual trunking takes place.

Again back to the original question. If he does a search for the frequency and holds on it, it will tell him if its DMR (OFT) or CAP,CON, T3.
That is the best way for him to determine what the frequency in question is transmitting.

 

[werinshades]

Assigning duplicate TG ID to each time slot is still a DMR Conventional set up. Uniden likes to muddy the waters (my opinion) by calling it a OFT even though its not actually trunking. There is no site controller. Its a conventional DMR channel that is using different TG with different time slots. The reason they like to call it OFT is so you can program in the different TG in different time slots and enable or disable them.
True trunking would be Cap plus, Con Plus or T3. The only trunking i am aware of with out a site controller is Hytera pseudo trunking. That will use the same TG but it can use either time slot. That is controlled by the hytera repeater and is proprietary to hyetra and is an option / feature they offer. But not many of them around that i am aware of. @werinshades im not arguing or disagreeing with you, just clarifying a bit. There are many ham repeaters around me who use different TG on different time slots. You do program them as OFT in a uniden scanner but its a DMR conventional channel as no actual trunking takes place.

Again back to the original question. If he does a search for the frequency and holds on it, it will tell him if its DMR (OFT) or CAP,CON, T3.
That is the best way for him to determine what the frequency in question is transmitting.

You're correct and it also allows radio ID's in OFT mode. I think the OP determined he has an OFT and has programmed it correctly.