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Thread: LTR - Not DMR,

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    Default LTR - Not DMR,

    Hi all,

    I know this is not DMR but couldnt find a section relating to LTR Trunking systems,

    LTR is not commonly used here, and have come across a system and looking for a basic overview of how it works if anyone could help ?

    So far my knowledge consists of

    Each repeater has a controller
    All controllers are linked together
    One controller is a master controller and the others report to this
    No control channel is needed
    No hang time on calls


    Questions I have are

    What is sent over the air from each repeater ? How does a radio know which repeater to use
    What pulls radios of interest into a voice call ?
    What is sent via a master controller versus slave controller channels ?
    What is the advantage of LTR ? just to do with no control channel capacity wasted ?


    Any other info on how it works ? We are not expected to do any work to the system and is being replaced with Cap Max but was more curious than anything ?

    thanks


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    Examples might be Trident's passport (before MSI bought and closed them down to protect Connect Plus) and Kenwood had I think it was called FleetSync.

    There are many others -- A Passport or Connect Plus to Cap Max is not a small move :-)

    -------------------

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    thanks, will look those names up

    The Cap Max system is standalone, and all new radios, so being build side by side and nothing reused so not been too difficult so far

    Quote Originally Posted by phonebuff View Post
    Examples might be Trident's passport (before MSI bought and closed them down to protect Connect Plus) and Kenwood had I think it was called FleetSync.

    There are many others -- A Passport or Connect Plus to Cap Max is not a small move :-)

    -------------------

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    Correct me if wrong, but there is no "master controller". Each home repeaters' controller validates if the group id for that specific home channel is valid. Every groups are identified by an area code (either 0 or 1), the associated home channel number, then a group id from 0 to 255.

    ie. 06-123 is group id 123 from the home repeater 6 with an area code of 0.

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    Apparently NOT a radio professional.

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    I also have access to a complete NTS Passport manual, but you DO NOT want to dig into that 600 page monstrosity.
    Apparently NOT a radio professional.

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    What is sent over the air from each repeater ? How does a radio know which repeater to use
    The radio will always contact it's home channel to request talk access. If the home channel is busy, LTR data will forward the radio to another available repeater.
    If the home channel is not busy anymore but the group conversation is still going on another repeater, the home channel will continue to transmit the data.
    If the home channel is unreachable, the subscriber won't be able to use the system.

    What pulls radios of interest into a voice call ?
    The radio will wait for data coming from it's home channel.

    What is the advantage of LTR ? just to do with no control channel capacity wasted ?
    The fact that it's a protocol that is available in many radios as a basic feature. It was easy and cheap to create a system with third party, external controllers from Trident, Zetron and many more.
    Nowadays I don't think it's really profitable to use LTR, especially with trunking system like Cap+ where you can have at least 4 voice groups going with only two repeaters.

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    Quote Originally Posted by MaxK98 View Post
    Nowadays I don't think it's really profitable to use LTR, especially with trunking system like Cap+ where you can have at least 4 voice groups going with only two repeaters.
    It doesn't lend itself well to any method of wide area linked system. It was meant as a stand alone single site. There have been some linked systems out there, but they were not stellar performers. RegioNet comes to mind. It never quite got off the ground. And as the world migrated towards ethernet transport, and DMR, LTR got left behind.
    Bow wow wow yippie yo yippie yay

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    Quote Originally Posted by radiotechs View Post
    What is the advantage of LTR ? just to do with no control channel capacity wasted ?
    That was it's one huge advantage - all channels available for voice calls. In urban areas with limited spectrum, having one more voice path was important. If you used a Trident system, you could run a positive subscription list to turn users on or off, collect air time statistics, and know exactly who was using the system. And because it was trunking, you could create talkgroups that truely separated traffic on common equipment. The other parties never heard each other. So, you could put competitors on the same community system, and they couldn't eavesdrop on each other. You could put casino security, facilities, food service, and housekeeping on the same system with priority given to security. They were very popular systems in the 90's that went out with the dodo's by the mid 2000's as DMR emerged.
    Bow wow wow yippie yo yippie yay

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    You will notice that one or more channels are "home" channels, which is where the radios try to start their calls at and then return to after they are involved in a call. The home channels are critical to not disturb. When we convert users from LTR or some other Trunking format to Cap Max, we will remove one of the "trunk to" channels and deploy a Cap Max control channel and a voice channel to perform testing. As the users turn off the LTR radios, we would remove those repeaters and add Cap Max repeaters. FB

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    Traditional LTR did not support the ability to disable a single radio, only entire talk group from the system. Which was a pain with leased radios! Unless you got creative with system setup.
    Most customers we programmed two home channels, one was for backup if repeater went down.
    So glad LTR was become a thing of the past for the most part.
    Radio Referenced...Those who think they know it all are very annoying to those of use who do.

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    I'm the guy who actually liked LTR It did what it was supposed to do, and did it well. It was simple & nearly foolproof. As other's mentioned, the real bugger from a system manager's standpoint was bandit radios.

    LTR is a constant subaudible data stream that's similar to DPL, but with some extra information bits. The radio homes to a specific repeater, listens to the datastream, and knows when the home channel is busy, and also knows if there's an available "trunk-to" channel that's open. Each transmission starts with a simple handshake, then you're granted access to either the home channel, or your transmission is assigned to another available repeater.

    There were some systems available which would hold hang-time for user groups, allowing continuing conversation to maintain their hold on a channel. Most systems though were transmission trunked, meaning if the system got busy, your reply could get busied out, but transmission based trunking increased the overall efficiency of the system.

    Trident Microsystems made the Passport networked controllers (which did add an ESN or some other mobile identifier to reduce fraud & increase system management/control) - and Trident ended up being bought by Motorola, which was pretty much the death of Passport. It's been almost 20 years since I messed with that, hard to believe.

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    I always thought LTR would be a lot of fun on the ham bands.

    Probably no point in bothering with it now when you've got DMR, though thanks to DMR, LTR controllers are now cheap and easily available.

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    Quote Originally Posted by phonebuff View Post
    Examples might be Trident's passport (before MSI bought and closed them down to protect Connect Plus) and Kenwood had I think it was called FleetSync.


    -------------------
    FleetSync is just a signalling system rather like MDC-1200. Similar functions & capabilities. Unit ID, both individual & fleet-wide calling, radio stun, etc. Worked on an LTR system that had FleetSync; the FleetSync could be used to turn off individual radios if they didn't pay their monthly rental fee.

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    Trident guys actually wrote the software for Connect Plus. We send out Connect Plus controllers to North Carolina to get serviced. FB
    Obviously NOT a radio professional!!

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    And a few of the key players still work at Moto and have Moto email addresses.
    Apparently NOT a radio professional.

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    wow, there are radio techs out there that don't know how LTR works smh

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    There are people that have never worked on 9600 baud modems too.
    Bow wow wow yippie yo yippie yay

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  29. #19
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    It is not a commonly used system where I am.
    I understand it is common in other places, we have either Conventional systems, Smartnet, Connect Plus, and Capacity Max.
    There is only one place I am aware of here using LTR and it is being phased out but have been dropped in on it, and no harm in asking questions

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    Quote Originally Posted by com501 View Post
    Awesome, thank you,. that should answer all the queries im sure

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    I doubt it's possible to top the files in com501's post in terms detail, but as a broader overview -- LTR has a sort of elegant simplicity, and has seen wide use here in the United States (at least) for a couple decades. It's cheap and pretty reliable.

    To specifically answer a few of your questions:

    Quote Originally Posted by radiotechs View Post
    What is sent over the air from each repeater ? How does a radio know which repeater to use
    All of the signaling is via subaudible data.

    Every talkgroup has a "home" repeater which it monitors continually. As a random example, let's say your radio is programmed for talkgroup 0-07-123. If we break that down:

    - The leading "0" is known as the area code, and it's either 0 or 1. This is the same value throughout a system (I think?), and in the wild it seems like it's almost always set to 0. It's just there so that if someone else on the same frequency is also running LTR (presumably on a faraway system that subscriber radios periodically hear if the bands are open), you can set up the system with area code "1".

    - "07" is your home repeater.

    - "123" is your talkgroup ID.

    Your radio, configured for 0-07-123, will always monitor the repeater at 07. However, if another user (let's say talkgroup 0-07-100) keys up, your home repeater is obviously not available at the moment. Since all the repeater controllers share a data bus, they all know which repeaters are available. The subaudible data stream being transmitted will indicate what the next repeater is, so when you go to key up on 0-07-123, your radio will know that, say, repeater 13 is the next free one.


    Quote Originally Posted by radiotechs View Post
    What pulls radios of interest into a voice call ?
    All the radios are following the outbound data stream and will see 0-07-123 come up on repeater 13. Those programmed for that talkgroup will unmute.

    Quote Originally Posted by radiotechs View Post
    What is the advantage of LTR ? just to do with no control channel capacity wasted ?
    The ability to use all of the repeaters for voice calls is indeed a big one. At the time it was seeing widespread deployment, I think the alternative wasn't really another trunking protocol; it was either dedicated repeaters, or community repeaters (multiple different groups of users sharing a single repeater, just using different PL tones).

    As MaxK98 said, the availability of radios from multiple vendors helped a lot, too. (To be honest, I've never even seen an EF Johnson LTR radio in the wild, even though they created it. But lots of radios made by Kenwood, Motorola, and Icom (and probably others) have built-in LTR support.)

    Here in the US, another detail is that, as I understand it, LTR can be licensed as an FB6 (or FB7) station class, which is more like a regular repeater. Centralized trunking systems require FB8 licenses, which are much more stringent in terms of what can be allocated. So putting an LTR system on the air was potentially a lot easier than something like a SmartZone system.

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    Default awesome, thanks thats very helpful

    thanks for that detailed info, that helps a lot

    It is the first system I have seen that was LTR and we are working on an aerial/feeder fault only, so wont get to play too much with the system.
    As it is being retired for Cap Max I doubt I will see another, but curiosity got the better of me as LTR is very rare here.


    Quote Originally Posted by fogster View Post
    I doubt it's possible to top the files in com501's post in terms detail, but as a broader overview -- LTR has a sort of elegant simplicity, and has seen wide use here in the United States (at least) for a couple decades. It's cheap and pretty reliable.

    To specifically answer a few of your questions:



    All of the signaling is via subaudible data.

    Every talkgroup has a "home" repeater which it monitors continually. As a random example, let's say your radio is programmed for talkgroup 0-07-123. If we break that down:

    - The leading "0" is known as the area code, and it's either 0 or 1. This is the same value throughout a system (I think?), and in the wild it seems like it's almost always set to 0. It's just there so that if someone else on the same frequency is also running LTR (presumably on a faraway system that subscriber radios periodically hear if the bands are open), you can set up the system with area code "1".

    - "07" is your home repeater.

    - "123" is your talkgroup ID.

    Your radio, configured for 0-07-123, will always monitor the repeater at 07. However, if another user (let's say talkgroup 0-07-100) keys up, your home repeater is obviously not available at the moment. Since all the repeater controllers share a data bus, they all know which repeaters are available. The subaudible data stream being transmitted will indicate what the next repeater is, so when you go to key up on 0-07-123, your radio will know that, say, repeater 13 is the next free one.




    All the radios are following the outbound data stream and will see 0-07-123 come up on repeater 13. Those programmed for that talkgroup will unmute.



    The ability to use all of the repeaters for voice calls is indeed a big one. At the time it was seeing widespread deployment, I think the alternative wasn't really another trunking protocol; it was either dedicated repeaters, or community repeaters (multiple different groups of users sharing a single repeater, just using different PL tones).

    As MaxK98 said, the availability of radios from multiple vendors helped a lot, too. (To be honest, I've never even seen an EF Johnson LTR radio in the wild, even though they created it. But lots of radios made by Kenwood, Motorola, and Icom (and probably others) have built-in LTR support.)

    Here in the US, another detail is that, as I understand it, LTR can be licensed as an FB6 (or FB7) station class, which is more like a regular repeater. Centralized trunking systems require FB8 licenses, which are much more stringent in terms of what can be allocated. So putting an LTR system on the air was potentially a lot easier than something like a SmartZone system.

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    Another popular technique around me was a multiax system. Mostly Philips/Simoco shops, I don't think any other vendors supported it.

    This basically gives you transmission trunking across a pool of community repeaters, using PL tones. Each user group gets a different tone.

    The mobiles scan the repeater pool for their tone, and unmute when they find it. When they transmit, they'll automatically search for and key up on the next vacant repeater.

    Mobiles generally have some smarts to share the load across the whole repeater pool; if a radio last keyed up repeater A, it'll try repeater B on the next over, and so on.

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    Quote Originally Posted by fogster View Post
    To be honest, I've never even seen an EF Johnson LTR radio in the wild, even though they created it.
    I owned an 8560 limited keypad portable at one time, but never had the programming bits for it. There were a couple of Multinet public safety systems in my area back in the day and a handful of SMRs.
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