No LOS, no problem!


Digital Repeater Backhaul allows IP Site Connect sites to be connected via a backhaul link that uses repeaters. This feature is especially useful in areas where no site link connectivity exists (e.g. Microwave).

This feature is supported by all the SLR series repeaters but not the (discontinued) MTR3000 or DR3000. Up to 14 backhaul chains are supported as well as up to 8 over the air hops per chain.

It supports all call types including Emergency call, All Call; Group Call; Individual Call; data and CSBK messaging.

All the repeaters in such a system can be monitored using RDAC - though the amount if information provided is limited when compared to IP-linked IPSC.
The repeaters support roaming beacons; NAI voice/data/control/phone; CWID and RAS. However, only standard GPS is supported - this means enhanced and single-CSBK GPS are not supported.

Transmit Interrupt; Repeater Call Monitoring; Digital Telephone Patch; Digital Voting; Confirmed Group Data and CSBK based data are also not supported in a Digital Repeater Backhaul system.

The sites at the beginning and end of a chain are known as the Origin and Terminating Site. The sites in between the the Origin and Terminating Sites are known as a Link Sites.

In a Digital Repeater Backhaul system, radios will talk (and listen to) to Drop Repeaters through regular DMR channels (just like a regular standalone/IPSC repeater). The Drop Repeaters repeat the calls over the air (just like a regular repeater) and send call streams to Link Repeater(s) over IP.

The Link Repeaters receive the calls from the connected Drop Repeater and forward this to the adjacent site/site's Link Repeater(s) through a seperate DMR link channel.

The Link Repeater(s) at the other end will receive the calls from over the air and send the call streams to its own Drop Repeater over IP.  and forward to adjacent site Link Repeater (except Origin & Terminating sites).

The frequency pairs (see above diagram) can be reused if there is no overlap between sites and/or links.

It's also possible to have a hybrid system consisting on regular IPSC repeaters and repeaters connected via a repeater backhaul - as shown in the diagram below.



Digital Repeater Backhaul makes an excellent substitute, or replacement, for EVX-link -  which was discontinued with the rebranding.


29 comments:

  1. What would a four site layout look like? Do the 'Link' sites in the middle require two repeaters each? If the drop repeaters are VHF, use UHF for the link repeaters?

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  2. Greetings Mr Holmes,

    are interim repeaters needed or would this work without them? For example, if we only have a master and one peer repeater in an IPSC, would Repeater Backhaul work with only an Origin and a Terminating Link repeaters?

    Cheerio.

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  3. Great news! I translated this article for my colleagues and customers.
    Thanx, Wayne!

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  5. Very Good Solution, Requirement is very high end from costumer. But..!
    It looks very complex architecture. Linking 3 repeaters required 4 additional Repeaters, Combiner and multiplexer,
    and Additional 8 frequencies. means for this solution required 14 nos Frequencies...? Very Expensive..
    There are two slots in repeater, If they use Slot 1 for RF-link and Slot 2 for Voice, then It will be the better solution.

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  6. hi guys! anyone had a chance to set the feature up and running? vendor's instructions is not clear enough.

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    1. There is, as far as I can remember, a job aid in the update training that covers the setup. Have you had a look at this?

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  7. Yes i had. The setup is described there though its a bit vague and i can not get it to work. My configuration includes 4 repeaters i.e 2 sites with 1 backhaul link.

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    1. ИЛЬЯ ВАЙНЕР, it looks like you and I are doing exactly the same thing at exactly the same time. Can we communicate tomorrow? Maybe we can compare notes.

      My email address is (phonetics for safety) mike lima uniform AT danimex.com

      I have been trying all day to get the link repeater to transmit, but no go.

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  9. hi Mr. Wayne,
    very interesting solution, but it's not clear to me whether the signal will be tied into the loop (in the analog the signal is looped into the loop).

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    1. This is a digital feature (there are other ways of doing this in analogue).
      You need to be careful about the frequencies - the link and drop repeaters need different frequencies.

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  10. Hi Wayne
    will the system pass both slots at the same time or is it any single slot at one time ?
    ie can site 1 have slot 1 and slot 2 in a call and that be relayed to the other connected sites over RF ? on a test system we have we are only able to use one slot at a time over the link it will pass both but only one will go over the link ?

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    1. If Slot 1&2 is selected in the channel then both slots are passed over the link.
      If this is not happening, you might have a configuration error.
      If SYNC cable is not correctly setup, this might also cause the symptom you're seeing.

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  11. Andy Griffith, in my test scenario I was able to pass both time slots simultaneously and in both directions as well. I picked up SIGNIFICANT RF issues with the test setup even though I use 20dB attenuators and short antennas on the Tx. We had the added problem of having the drop and link repeaters on VHF, but once the RF issues were sorted out, the system appears to work very well.

    The documentation I had on the implementation was confusing and in places actually wrong, so it took a lot of playing and fooling around to get it to work.

    I am pretty sure that Motorola will be reviewing their documentation as time goes by.

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  12. thanks both for the reply i belive what we are seeing is connected to talkgroup timers will extend then and test futher , any chance for sample code plugs to compare ?

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  13. Sure. I have the codeplugs and some documentation available, but not sure how to share them here.

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    1. Here is a presentation I made at work. It will also go on Motorola Online sometime soon. http://bit.ly/2Lx212o. This might answer the question.

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    2. Hi Wayne, nice document. I'm glad to see you simplified the terminology and called the repeaters "standard" and "link". I also like the fact that you simplified the sync cable to be bi-directional... makes much more sense.

      I have two questions:
      1) Motorola told me that I had to use the same UDP port for the standard repeater and the link repeater at each site. This appears to work, but I see you've done it differently. Any comments?

      2) How would a sync cable look if you added a standard repeater to the interim site in example 2? I suspect you just parallel pin 23 and ground, make one link repeater the output and the others all inputs?

      We'll be testing this all out during the next two weeks :)

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    3. You can use the same UDP port. I prefer to use different ports (old habit from Linked capacity Plus) as this sometimes makes things easier to diagnose (e.g. when looking at Wireshark captures).

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    4. I did not include that but since the GPIOs are high impedance you would just parallel the inputs to the output. So one repeater would generate sync and the other two would receive sync.

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    5. I'm a great fan of testing in house before deploying - even if it's not a fancy FAT like we do at work and even for small systems.
      Nothing worse than having the customer peer over your shoulder while you're scratching your head (ask me how I know :-)).

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    6. (Sorry, for some reason I was logged out of my Google account, so my previous post looks anonymous)

      Agreed on point 3. We don't have a customer lined up though right now, but we're getting a lot of questions about it so we need to understand it properly. I think I will be doing a small in-house presentation on it in the next two weeks or so.

      OK, we were wondering why we were told specifically that the UDP ports had to be the same. We'll try both and see if makes any difference.

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    7. There were some mistakes in the document. These have now been fixed and an updated version is at the link http://bit.ly/2Lx212o.

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  14. We in Norakom have testet in our lab 3 sites with voice repeaters and it's working fine.
    You have to setup IPSC slot 1 and slot 2 on link repeaters, same port numbers on all repeaters on each site. On the radios you must turn on Private call confirmed and Data call confirmed.

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  15. Correct - see http://bit.ly/2Lx212o

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  16. Great document and post!
    quick question. im guessing that if i use UHF for the "access" repeaters i can use VHF for the link repeaters?

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    1. You can have the link in the same band or in a different band. Using a different band just makes RF filtering easier.

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