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System Administration and Maintenance - Here is where radio system managers can discuss some of the more intricate details of managing their complex radio systems.

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  #1 (permalink)  
Old 09-03-2017, 3:12 PM
Join Date: Oct 2015
Location: Lowestoft - UK
Posts: 355
Default User management on digital systems

Please forgive me for asking what will no doubt be considered a daft question, but I'm thinking about changing one of my repeaters to a DMR version.

It's a small area system here in the UK, and just three users, each with a different CTCSS and they exist with little co-channel issues.
User 1 is a small business with very little traffic
User 2 is similar, and again has very little traffic
User 3 is based around vehicles all talking to each other and while traffic is heavy, it's concentrated in the evenings and night time when the other users are hardly ever working.

The repeater is on permanent talkthrough and coverage is not an issue.

I also use it myself occasionally on a fourth CTCSS tone.

My question is simply how you manage multiple users on a DMR single repeater. I could put the must user on slot 1, say cc1, but how do I separate the other two, or even three users if I include my own occasional use of the system. Does the repeater repeat anything it receives on both slots, or is some kind of processing involved that limits or blocks traffic on certain CCs.

My concern is that if it repeats everything, then if somebody added their own radio on a different cc - I wouldn't be aware of it, and they could get free use of my system. Looking at the manuals for the repeaters I'm thinking about, they don't make any of this very clear at all.

Can they all offer me 3 separate users, each independent? Or will certain brands do this while others won't?
If it helps I'm looking at a Hytera 620 series - probably a 625, but I don't need IP connectivity - but the three user thing is essential.

This also appears to offer analogue AND digital, so could I migrate the busy user to digital, while leaving the other two for a while on analogue?
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Old 09-30-2017, 11:39 PM
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I'm certainly not an expert in DMR but here is some information to get you thinking -

It appears to me as if the biggest advantage to using DMR in your situation would be the effective upgrade from a single talk path (analog channel) to two independent digital talk paths. I believe that if you mix analog and digital on the same repeater, you would lose this advantage.

As I understand the process, when you set up the software of a DMR repeater, it's up to you to specify how many digital talk groups (and which ones) you will "activate". Overall, you would have MUCH more control over your repeater than would even be possible with a analog repeater, and each of the different users (companies) could have their own discrete talk group. Pirate users would not be able to use talk groups that are not authorized, and you would be able to lock out individual radios from your repeater should it become necessary.

One really big consideration, however... In order to transition from analog to DMR, all of the associated radios must be capable of DMR (digital) operation. Otherwise, you would lose virtually all of the advantages of digital operation. This could be a big expense for you and/or your repeater users.

Best of luck.
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Old 10-01-2017, 5:08 AM
Join Date: Oct 2015
Location: Lowestoft - UK
Posts: 355

This is the snag - one user isn;t really op[en to spending money of any kind as in his words "we only use it twice a day to get everyone in the right place and ready to start, then the next message will be at going home time" I see his point.

What I'm not seeing in the CPS for the repeaters I've had an interest in is much in the way of control. One is able to work in mixed mode, with multiple CTCSS operation for analogue users, but most of the digital functions see, to relate to the single digital setup - I still can't work out if there's any control over the two repeater slots. I can set the repeater to it's frequency, mode, and slot - but I assume this to be just what comes out of the speaker and goes in the repeater mic - if something appears on the input on either slot, it goes out, and the programming just controls what I hear and who hears me while I'm next to the repeater. If this is wrong, then nowhere does the CPS seem to indicate any gate-keeping type functions? If it does repeat anything, then I have no real control. If it only repeats what the CPS allows me to set, then if the operational channel is slot 1, then slot 2 won't be an option? Also - if it only repeats what users are in the lists with ID numbers, then it will be a visit to the repeater every time I add or swap a radio from the system? As for the IP control - nowhere does it provide any information on this - if it let me remote programme it that would be one solution, or part-solution, but I don't think it does - it appears to simply pass the data stream to the network, and receive back additional data - making linking repeaters pretty simple with fixed IP at each end.

The Chinese suppliers have been totally hopeless with repeaters. Constantly having to ask the factory questions on almost every query. One I've been considering is built around two modified FM mobiles inside the case (HYT do this in one of their smaller ones, the TR-50, with two heavily modified portables.

In the DMR repeater - there is a DMR processing board than take the discriminator feed and does digital 'things'. Quite what is does is a mystery. If only somewhere there were proper explanations it would really help.
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Old 10-01-2017, 9:35 AM
Join Date: Jun 2013
Location: Texas
Posts: 3,115

Sorry for the post delay. I was writing a reply at 2320 my time and got a phone call from my oldest's grandmother about something crazy my ex is doing an within 10 minutes I was in my pickup on my way to the other side of the state 300 miles away…makes for a long night.

Anyway, what I was originally going to say (when I was replying on my laptop) was Motorola has no form of user/talkgroup management for Tier II DMR (can't confirm the same about Hytera). Traditionally what would be done is the division of useres across the two talk groups however, with most major manufacturers offering pseudo trunking options for a single channel that is actually the best way to go. Think of it as a two channel LTR system with less bulk. Users get the first "available" slot when needed and aren't really tied to an assigned slot.

The big problem, pseudo trunking isn't part of the Tier II or Tier III standard so it is proprietary to each manufacturer. Honestly, I'd recommend Simoco Xd line of repeaters (not just because they are a U.K. company) as they do feature what Simoco calls simple repeater, dual slot (pseudo trunking on a single channel), user/talkgroup management in terms of white and black listing, and true mixed mode operation with out having to purchase any kind of EID or license for the hardware. Just my opinion based on your needs and wants.

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Old 10-01-2017, 11:09 AM
Join Date: Oct 2015
Location: Lowestoft - UK
Posts: 355

Thanks for that. It does seem a missed opportunity in the range of repeaters. Around here there is a VERY strong DMR system, and while it's does operate on a number of frequencies, the main transmission is easily heard within around a 50m radius of where it is based, designed to talk mainly to offshore vessels, and spends most of it's time giving permits for dozens of people to work in normally unmanned locations. It uses a main talkgroup, and then a smaller quantity of users, who seem to be supervisory, who use a different one on the same slot. If some unscrupulous person was to set up a totally new talkgroup, then the authorised users would be totally unaware of the hijacking of the system. This seems a very large flaw, and if these users engaged encryption, then the owners of the system would be unable to find out what is going on - if they detected the unauthorised usage, perhaps if messages clashed and didn't get through, considering the often long path lengths involved, maybe they'd just assume the failures to be a function of distance. If they did work out what is happening it would have to be by the DSD type software, which would show the presence of a new talkgroup and radio IDs. There really should be some kind of security, or at least a monitoring system without using a outside sourced solution. If you actually tracked down the system was being hijacked, with encryption you'd be left with just DF as a tool to find out who or what was going on?

I'll have a look at the Simocos - we do see these here in the UK, but I'd not thought to check their digital offerings.
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