'DMR Conventional Networked' Question

[PriorMike]

(Apologies if this has been asked before)

So more of the type of system seems to be showing up here in Ontario, mostly by fire departments:

https://www.radioreference.com/apps/db/?sid=9201
https://www.radioreference.com/apps/db/?sid=9118
https://www.radioreference.com/apps/db/?sid=10130
https://www.radioreference.com/apps/db/?sid=10097

How, exactly, do these systems 'work'? They're not trunking; given that each site has a separate frequency how does 'your' radio know what frequency to operate on?

I'm kinda confused...

 

[troymail]

Based on the listings you've provided, I suspect that each "channel" is fixed/dedicated/indicated by the TG and slot on the frequency (essentially using the frequency/slot as if it is a "conventional channel").

The only different between a single large area repeater frequency and these "two site" configurations is that there are two repeaters - similar to true full-blown multi-site trunking systems - subscriber radios affiliate with whichever site is best given that user's location.

With two repeater frequencies/sites vs. one, it seems logical that the power and coverage area could be reduced on each since each only has to cover a smaller specific area.

Of course, these are just assumptions ....

 

[Mr_Boh]

On DMR 2 slot repeaters if there is no traffic, the repeater has the capability to transmit a beacon on slot 1 to allow subscribers to automatically select the closest repeater. This is what most people refer to as “roaming”. There’s a lot to be found on the subject and some of the amateur DMR users are implementing it on networks that have multiple repeaters offering the same talkgroups so that an operator doesn’t have to flip the knob when switching repeats. Subscriber uses RSSI of the repeaters in the roam list to determine best one.

DMR-MARC touches on it briefly here.

More good info here too.

 

[PriorMike]

Ah, so the 'best' repeater is automatically selected based on signal strength depending on 'your' location.

Since the repeaters are networked, those subscribers on the same TG/Slot on the other repeater still get the transmission, therefore enabling smaller organizations to have multiple repeaters without having to get into the complexity of solving simulcast issues if they were operating on the same frequency, correct?

 

[Mr_Boh]

Ah, so the 'best' repeater is automatically selected based on signal strength depending on 'your' location.

Since the repeaters are networked, those subscribers on the same TG/Slot on the other repeater still get the transmission, therefore enabling smaller organizations to have multiple repeaters without having to get into the complexity of solving simulcast issues if they were operating on the same frequency, correct?

You got it mostly right - it’s not really simulcast issues since in simulcast, all repeaters have the same frequency, toning/NAC, etc. The repeaters are not synchronized like a simulcast so either you could do the same frequencies with different color codes or use separate frequency pairs altogether.

There’s a couple other factors - for example a talkgroup might not be active at a repeater unless the subscriber keys up to activate the desired talkgroup. Then there’s a timeout period before that specific repeater stops transmitting that group’s traffic. However, in the examples you provided, you see that there are only two talkgroups each tied to a time slot. So I’m willing to bet all repeaters in the network are always broadcasting any traffic in either talkgroup.

If you want a more complex example, look at networks like DMR-MARC in Maryland or DMRVA in Virginia, then check out the websites for each of those clubs. You will see that the individual repeaters will tie down certain talkgroup a while others require keying to activate. Also some of the networks have enabled the “beacons” to support roaming and some will require the users to manually select the appropriate tower.