Digital Trunking (DMR Tier 3, P25, NXDN) on Amateur Bands?

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andrewket

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Is anyone aware of a digital trunked system running on amateur radio? We have a multi-site multi-channel DMR system up and running and are thinking about taking the next natural step. Would love to connect with anyone who has done this already.

73,
Andrew
N9KET
 

GrumpyGuard

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Andrew,
The DMR radios that are made specifically for amateur use are tier one and tier two radios. These radios won't allow trunking.
 

kayn1n32008

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Is anyone aware of a digital trunked system running on amateur radio? We have a multi-site multi-channel DMR system up and running and are thinking about taking the next natural step. Would love to connect with anyone who has done this already.

73,
Andrew
N9KET
I am aware of one.
 

2IR473

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I’m curious how adding a trunked repeater system to the amateur community would be a benefit ? Beyond the cool factor of actually getting it to work, how would it be better than what already exists with RF and VOIP-linked systems?

And doesn’t a trunked system require several frequencies ? So you be required to coordinate those frequencies through your regional coordination council, and that might be a major PITA ? I have heard this idea floated in the past, and I am just curious about the ”how” and “why” when it comes to amateur radio. Thanks for any explanation.
 

kayn1n32008

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I’m curious how adding a trunked repeater system to the amateur community would be a benefit ? Beyond the cool factor of actually getting it to work, how would it be better than what already exists with RF and VOIP-linked systems?

And doesn’t a trunked system require several frequencies ? So you be required to coordinate those frequencies through your regional coordination council, and that might be a major PITA ? I have heard this idea floated in the past, and I am just curious about the ”how” and “why” when it comes to amateur radio. Thanks for any explanation.
By using a trunking format like Cap+, or XPT you can have a trunk site have only a single channel.

Capacity Plus and XPT do not have control channels. They dynamically assign a time slot based on load. If the system is busy, then add a second channel.

You can also have a mix of bands. With Cap+ you can have a VHF, UHF and 900MHz repeaters all at the same site and have talkgroups across all bands or a combination of bands. Another advantage of Cap+ is not needing a controller. All logic is handled by the master repeater, RDAC allows you to remotely see what’s going on with each repeater(if you have internet connectivity to your site. Remote access also allows you to control what talkgroups appear on what sites/repeaters, and white/black lists control access. Unfortunately Motorola refuses to sell AES in the NA region, RAS will keep those that don’t want to contribute from accessing the system, and while EDP is welfare encryption, and 110% owned, it keeps scanners out as well. If AES is desired, Hytera will happily sell AES to its customers, and XPT using Hytera infrastructure and subscribers is another, low(er) cost way to bring trunking to amateur radio.
 

kayn1n32008

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I’m curious how adding a trunked repeater system to the amateur community would be a benefit?
At one time amateur radio lead the curve in inventing and adopting new communications technology. That ended in the 80’s. Hams are, more or less, content with annoying talking controllers that make all sorts of beeps and boops, all on carrier squelch repeaters, with horrible audio. Hell most places are still stuck on thinking we should only use 30KHz channels. Hell the hammy manufacturers can’t even build a radio to properly do analogue 2.5KHz deviation. It’s pathetic

Beyond the cool factor of actually getting it to work, how would it be better than what already exists with RF and VOIP-linked systems?
Dynamic time slot assignments is a game changer. Too bad there is not a DMRA standard for a Cap+ type tier 2 time slot trunking format.

As for RF linked and VoIP linked systems, analogue linking is reliable(usually) but there are inherent issues with audio quality, and it’s still analogue and susceptible to the wildly variable audio levels of the users operating style and equipment. Same with ROIP. control of the links is cumbersome, by having to control it with DTMF.
 

kayn1n32008

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So you be required to coordinate those frequencies through your regional coordination council, and that might be a major PITA?
It would be no different than coordinating for a conventional repeater.

If multiple repeaters, on the same band, are needed at the same location coordination would likely be an issue, due to OF hams stuck in the past, ones with a clue should have no issue.

The issue is doing a proper IM study to ensure the frequencies selected are not going to cause a 2-5 Ofer IM product, that’s going to cause issues to the system, or others at your site. A lot of issues can be avoided by using proper RF design, and building a proper plumbing system to keep RF out of places it should not be.

The biggest issue is going to be dealing with a coordination council like we have where I live.
The usual answer is ‘nothing available’. I recently found 28 usable pairs for a new repeater site being built. Again, OF hams living in the 80’s with their out of date 30KHz channel band plan.
 
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kayn1n32008

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Cap+ and XPT also have an indirect advantage. It has a ‘barrier to entry’ in the cost of subscribers. While Gen 1 Motorola subs are pretty cheap, they suck and have ****ty audio. Hytera radios are not cheap either.

However, with patience, deals can be found. I got my UHF XPR7550 for C$200, and my 25w VHF XPR5550 for C$300 and a remote kit for C$195.
 

kayn1n32008

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Means nothing. Plenty of Gen 2 radios around here have working AES. Matter of fact, AES is loaded in every Gen 2 radio sold in the USA. It’s just a matter of unlocking it. And no key loader is needed to enter the key. The laptop enters the key.
Agreed. However it requires ‘skills’ not discussed in public. The average user is not going to be using AES with Motorola DMR gear.

Discussing how to activate AES in gen 2 NA Motorola subs will get scum bags like Peter Wilt with HSI coming to your door, or detaining you in an airport, accusing you of supplying AES to drug cartels and terrorists.
 

Project25_MASTR

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I’m curious how adding a trunked repeater system to the amateur community would be a benefit ? Beyond the cool factor of actually getting it to work, how would it be better than what already exists with RF and VOIP-linked systems?

And doesn’t a trunked system require several frequencies ? So you be required to coordinate those frequencies through your regional coordination council, and that might be a major PITA ? I have heard this idea floated in the past, and I am just curious about the ”how” and “why” when it comes to amateur radio. Thanks for any explanation.
The major downfall to DMR (as built by the amateur radio community) is how it was built. Originally, the setup called for a local timeslot (not linked to anything) and then a linked time-slot which carries multiple talkgroups. The downside to this, if a local timeslot is busy a user at the remote site has no way of knowing and the traffic to the remote site is simply never received. Creates missed traffic all over the place especially when multiple local users are fighting for different talk groups on the same timeslot. This is not an issue limited to amateur radio but it is most prevailiant with amateur radio (that being said if a commercial customer has more than three talk groups in use for a standalone DMR repeater they really need to look into a small trunking system).

The quick solution is to convert the system to a pseudo trunking format such as Motorola's Capacity Plus or Hytera's XPT. We call this pseudo trunking because it is not true control to the system. Timeslot assignment is based purely on the concept of next available timeslot. Essentially, if someone is actively using timeslot 1 the system will automatically direct the next incoming call to timeslot 2 (regardless of what the TG is). If all timeslots are busy, then the users will get a notification when they try to key up but will receive a notification when a timeslot is available. This also scales to multiple repeaters at a site. DMRA really screwed up when they failed to define a pseudo-trunking standard. Pseudo-trunking came about partially because it took DMRA nearly 5 years to created the Tier III standard (by that time Motorola and Hytera had both created pseudo-trunking formats and Trident Micro systems (the guys behind LTR Passport) had created Connect Plus trunking (and would later be bought out by Motorola). One of the big issues with pseudo-trunking though is that you can still have some network hangups due to not having enough resources or a site trying to pass more remote talk groups than it has capacity for (which is where control based trunking comes in).

Control based trunking requires a controller...typically multiple. The advantage to control based trunking is that is smart. A zone controller watches a group of sites. Site controllers then control the repeaters at the sites. When a user at a site selects a talkgroup, a request for affiliation is sent to the site controller. The site controller checks with the zone controller to see if that user can use that talkgroup and if yes will tell the site controller what other sites that talkgroup has affiliations (so the traffic can be routed appropriately). The benefit to this, traffic doesn't pass to sites where there are no active affiliations to a talk group (i.e. you don't key up repeaters where no one is listening to the talkgroup). Very efficient but can also be quite costly (Simoco's Xd is the cheapest Tier III solution at the moment as the function of the Zone Controller and Site Controllers are built into the Xd repeaters).

Now, DMR Tier III can operate on a single channel trunk (one timeslot for control, one for vocie). P25 can also operate on a single channel trunk (control channel will drop for a call).
 

Project25_MASTR

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Septura Tier 3 infrastructure has a controller built in each repeater, I believe.
So does Capacity Max...you just need the "Zone Controller" i.e. two HP servers running ESXi with HA running a single instance of the Zone Controller software in a VM. You also need a RM server but that's a whole different story. Mother M charges a pretty $25,000 for that nearly. Used to have a customer who'd Cap Max system would lock up every 3 or 4 months due to the zone controller having some sort of brain fart. That one system was so troublesome our sales reps swore off of Cap Max.
 

N4KVE

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Agreed. However it requires ‘skills’ not discussed in public. The average user is not going to be using AES with Motorola DMR gear.

Discussing how to activate AES in gen 2 NA Motorola subs will get scum bags like Peter Wilt with HSI coming to your door, or detaining you in an airport, accusing you of supplying AES to drug cartels and terrorists.
I bought my 7550 second hand. This is what the seller told me. And we keep it simple here on our DMR repeaters. Every repeater except for one has only one TG on a TS. So if you don’t hear someone talking, you won’t get a busy bonk when you key up. DMR as it should be.
 

andrewket

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Andrew,
The DMR radios that are made specifically for amateur use are tier one and tier two radios. These radios won't allow trunking.
That's ok. Many of our users have Motorola radios, or would be willing to buy commercial if we make the move.
CCRs won't trunk, but there are plenty of UHF (~400-470 MHz) DMR radios that can handle the job.
Yep. Our current system is UHF. We have experimented with 900mhz but the availability of hardware is very limiting.
Tait, Hytera, Kenwood and Motorola all produce Tier 3 capable radios. All make radios that cover the 2m and 70cm ham bands.
Our current repeaters are Motorola, and I had assumed we would stick with it. Having said that, having done just a little research so far, Tait and Kenwood have some impressive products. For example, simulcast with sync over IP looks easy to implement.
I’m curious how adding a trunked repeater system to the amateur community would be a benefit ? Beyond the cool factor of actually getting it to work, how would it be better than what already exists with RF and VOIP-linked systems?

And doesn’t a trunked system require several frequencies ? So you be required to coordinate those frequencies through your regional coordination council, and that might be a major PITA ? I have heard this idea floated in the past, and I am just curious about the ”how” and “why” when it comes to amateur radio. Thanks for any explanation.
We currently have 3 UHF pairs coordinated, with a request in for a 4th. The major benefit is getting out of traffic management. Right now we have contention between TGs that are currently on the same channel and time slot, while a time slot on a different channel sits idle. As the system owner we could move the TG to a different channel/slot, but it requires a massive undertaking to get every ham out there to update their codeplugs/radios. Trunking allows users to use all the TGs that are available with no contention (unless of course we get to a point where we're using all channels all the time, which is highly unlikely.) With some trunking technologies we can even add additional sites/channels without any codeplug changes. It's all exchanged on the control channel over the air.
I think it would be great to have a trunking system available. No need for everyone to sit on one or two talkgroups or tie up the entire system. Private calls (encrypted or not) that don't bother others, etc. Hell, why not?
Exactly. Plus, it's amateur radio. Isn't the entire point to experiment?
 
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