DMR Primer?

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Kirk

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I'm starting to get the DMR bug a bit after finding a DMR system just went on the air in my area. I'd like to understand a bit better how this works.

Specifically:

It appears the repeaters support multiple talkgroups, split between two timeslots. Does the subscriber unit affiliate with the repeater when it's turned on (without the user keying up)?

If I key up a radio on the right talkgroup, it makes sense that it could be routed to the right place, but if I'm just monitoring, how does the repeater know which talkgroups to transmit?

I monitored the local frequency on my drive in today and heard nothing (on an analog radio). I expected to hear digital noise. But maybe there's only noise if there's an affiliated subscriber unit in the area?

Just trying to sort this all out.
 

WA0CBW

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It is a "goz inta-comz outa" operation. Whatever talk group/time slot goes in is what it comes out. If you are monitoring a talk group/timeslot you will hear it but if you are monitoring a different talk group or timeslot you won't hear anything. You can have two simultaneous conversations going as long as one is on time slot 1 and the other is on time slot 2.
 

Kirk

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But say timeslot A is capable of talkgroups 1-5 and timeslot B can do talkgroups 10-50, and there are five hams on that repeater, each monitoring different talkgroups, how does it decide what to transmit?
 

WA0CBW

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It transmits the talk group/time slot that comes into it. If I transmit on talk group 5/time slot 1 then the people on talk group 5/time slot one hear me. None of the other talk groups/times slots hear the conversation. The repeater is a pass through for the specific talkgroup/time slot it hears. There is no affiliation of units. The repeater is a dumb box.
 

Kirk

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Thanks, John. I'd seen that earlier on a mailing list and it's a good start.

What I'm wondering is what happens in the following scenario:

User A is monitoring TS1, TG1.
User B is monitoring TS1, TG9
User C comes onboard, and initiates a conversation with User A on TS1, TG1.
User D turns on his radio to TS1, TG9. He doesn't hear the conversation between A&C because he's on a different talk group. What happens when he tries to call User B? Does he get a busy tone, etc? Is there a way for the repeater to assign levels of priority to certain talkgroups, or is it just whomever's first wins?
 

KE5MC

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Couple of sites I did not see in other posts you might find useful. The CS700 at the current internal software level has to be programmed from a PC. Software free, cable $5 and radio $180. It can scan, but only what you have programmed. It trasmits (4w) and is used by many hams. Second link works, but link name not what I expected. Goes to Connect Systems site for the CS700.


DMR-MARC Network

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I'm starting to get the DMR bug a bit after finding a DMR system just went on the air in my area. I'd like to understand a bit better how this works.

Specifically:

It appears the repeaters support multiple talkgroups, split between two timeslots. Does the subscriber unit affiliate with the repeater when it's turned on (without the user keying up)?

If I key up a radio on the right talkgroup, it makes sense that it could be routed to the right place, but if I'm just monitoring, how does the repeater know which talkgroups to transmit?

I monitored the local frequency on my drive in today and heard nothing (on an analog radio). I expected to hear digital noise. But maybe there's only noise if there's an affiliated subscriber unit in the area?

Just trying to sort this all out.
 

w2xab

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RX Lists

Thanks, John. I'd seen that earlier on a mailing list and it's a good start.

What I'm wondering is what happens in the following scenario:

User A is monitoring TS1, TG1.
User B is monitoring TS1, TG9
User C comes onboard, and initiates a conversation with User A on TS1, TG1.
User D turns on his radio to TS1, TG9. He doesn't hear the conversation between A&C because he's on a different talk group. What happens when he tries to call User B? Does he get a busy tone, etc? Is there a way for the repeater to assign levels of priority to certain talkgroups, or is it just whomever's first wins?
Most amateurs program RX lists for the two different TSs so they will hear everything on a TS. My TG9 channel is programmed on TS1 and the RX list includes TG1, TG3, and TG9; this way I will know that the TS is in use. TGs do not have priority, FIFO.
 

Stupidfatkid

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User D turns on his radio to TS1, TG9. He doesn't hear the conversation between A&C because he's on a different talk group. What happens when he tries to call User B? Does he get a busy tone, etc? Is there a way for the repeater to assign levels of priority to certain talkgroups, or is it just whomever's first wins?
If user D presses the PTT while user A or C is actively transmitting user D will receive a channel busy tone. Also referred to as getting "bonked". This is assuming you're following the subscriber setup recommended by DRM-MARC. Channel access controls are programmed into the radio not the repeater. Section 2.2.3 of the MOTOTRBO System Planner covers the topic in detail.

I noticed you posted your question to the Trunking Forum. I'm not sure if your original question referred to amateur DMR repeaters or commercial DMR repeaters. I haven't seen trunked DMR repeaters on the amateur bands. All the repeaters I've seen are single channel systems with two time slots.
 
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Kirk

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I've been at this long enough that I should have known better. I posted to the wrong forum. I am talking about amateur DMR, not trunked.


Thanks for the info.
 

N8NQP

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Ok, lemme give it a shot...

Time slots - Think of them as repeaters. Just like you have to be on the machine that you want to hear something on, the same applies (we will leave linking out for now)

Talk Groups - These are just another way to keep the subscriber unit (the radios) quiet when there is traffic that they don't want to hear. What you can do with talk groups that is different than say ctcss is that you can have multiple talk groups monitored. That said the channel you set up can ONLY TRANSMIT a single talk group. Typically I am programming a Monitor slot 1 and a Monitor slot 2 channel that are receive only. I then use a 1 to 1 on the other channels (so the receive group matches the transmit talk group.) The reason I do this is so I can spin thru the channels and FIND the talk group that I need to use so the folks I am hearing will hear me.

The idea of creating receive groups that can hear everything is good up to the point that you will often hear people that you can't talk to, and with the PTT talk groups that are set up in the C-Bridges, you could knock someone off the machine. (I.E. local has priority and you key up while someone was on TG 310)

-Mike
 

N8NQP

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Most amateurs program RX lists for the two different TSs so they will hear everything on a TS. My TG9 channel is programmed on TS1 and the RX list includes TG1, TG3, and TG9; this way I will know that the TS is in use. TGs do not have priority, FIFO.
This is where it gets tricky...

If there is a C bridge involved, they can have priority, I am speaking specifically of the PTT talk groups.
 

AA9VI

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I'm starting to get the DMR bug a bit after finding a DMR system just went on the air in my area. I'd like to understand a bit better how this works.

Specifically:

It appears the repeaters support multiple talkgroups, split between two timeslots. Does the subscriber unit affiliate with the repeater when it's turned on (without the user keying up)?

If I key up a radio on the right talkgroup, it makes sense that it could be routed to the right place, but if I'm just monitoring, how does the repeater know which talkgroups to transmit?

I monitored the local frequency on my drive in today and heard nothing (on an analog radio). I expected to hear digital noise. But maybe there's only noise if there's an affiliated subscriber unit in the area?

Just trying to sort this all out.
We have listed an Amateur Radio Guide to DMR by W2XAB on the dmr-marc.net website under Member Toolbox.
 

Kirk

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I got my CS-700 this week and both local repeaters have lost their network connections. Sigh.
 

Kirk

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This thread is two years old... I'm quite up to speed on DMR these days. :)
 
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