Extended Range Direct Mode

Extended Range Direct Mode enables repeater operation on a simplex radio channel. Radios on an ERDM channel transmit on one slot and receive on another slot - the frequency is the same.

With this you get:
  • Repeater-like coverage
  • No need for a 2nd frequency - your simplex channel can be reused.

In this configuration, dual slot operation is not possible and you need to be using a SLR series repeater. IP based dispatch solutions, like SmartPTT Plus and TRBONET Plus, are supported. It also only supports single site conventional operation so no trunking or IPSC.

This feature requires R2.7.0 firmware and is supported on all current generation MOTOTRBO radios. My understanding is that this feature will also work on other makes of DMR radios.

Postscript 20.01.17

Before deploying ERDM, you must check with your local authorities as a simplex frequency licence is tied to a smaller geographical area (i.e. no more than 5km from point X is allowed). Installing a repeater (even though it uses a single frequency) may violate your licensing conditions.

- Thanks and credit to Craig Matthews for pointing this out.

Postscript 04.03.17

A Circulator cannot be used as it does not offer sufficient isolation (<30dB).

- Thanks to Jim for trying this out. Even a negative result is a result. 

Postscript 30.05.18

The SLR1000 has an optional built-in high speed antenna switch that will allow the repeater to be used with a single antenna. The same could be said about the other repeaters but Motorola doesn't produce an antenna switch for them unfortunately.

The antenna relay cannot be used as this is an electro-mechanical device that cannot cope with the high speed switching.


  1. Very good news, Great Wayne


  3. Do we need two antennas for the repeater to work in single frequency direct mode ?

    1. This seems to be the easiest way to arrange the antenna system.

      There is mention in the system planner of switching a single antenna between receive and transmit by using an output on the accessory connector but I don't have any details.

      I thought of using a circulator but have never tested that.

    2. The MOTOTRBO CPS help show:
      Antenna Relay Delay Timer (ms)
      This feature is applicable to MOTOTRBO Conventional and MTR3000 base radio/repeater and SLR series repeaters in Analog mode only.
      so, maybe can't use at this case?

    3. Antenna Relay is for when the repeater is being used as a base station and has nothing to do with ERDM.

    4. I test the SLR8000 in Extended range direct mode using an circulator as you suggested. I manage isolation of 28,5 Db between TX and RX port, it is working with 6 watts Rf power with no indication of desensitization, of coarse I used a antenna with very low VSWR. But I am afraid to use more power, after all SLR8000 is an expensive repeater! What is your opinion?

    5. I would not use a circulator then. Thanks for doing this test. I'll edit this post to reflect your feedback. :-)

  4. I upgraded a SLR5500 and some DP4801 radios to firmware version R02.07.00.04 and I realised that "Extended Range Direct Mode" feature was needed to purchase for SLR5500 repeater. It's not a free feature. I could not see the price of this feature in the current repeaters price list which is published in the MOL.

    1. List Price : $400.00

      Part Number: HKVN4490A
      • License key required to activate the
      "Extended Range Direct Mode" feature in
      an SLR 5500 / SLR 8000 repeater.
      • Also known as "Single Frequency
      • Significantly increases coverage area on a
      single frequency beyond a direct mode
      • Does not require additional frequency
      usually required on a repeater.
      • Inbound burst is repeated 90 ms later on
      outbound (time division duplex).

  5. show the correct settings EXTD RANGE DIRECT MODE in portable radio DP4801, SL4010

  6. We have done some testing of ERDM here in Denmark, and it is really very clever... The radios operate in ERDM when a repeater is present, but when you go out of range of the repeater, the radios continue to talk to each other in simplex. This seems to happen seamlessly, so you don't drop a call when you go in or out of repeater coverage.

    According to someone on Radio Reference, the following relays are recommended by Motorola for use with a single antenna. The relay is driven by the accessory connector. I haven't done it yet, but it's on my "to do" list.

    0310909E68 SCRTPG,M4X0.7X35,STARPAN STL ZINC( 2 req’d)
    30009310002 CABLE, ANT RELAY DC
    40009272001 COAXIAL RELAY, 14V

    My next task is to see what we can do about System Bridging two ERDM repeaters using TRBOnet :)

    I think that ERDM is one of the most exciting developments to come out in years.

    1. Be careful not to use an electromechanical relay, it'll struggle to keep up with the 30ms switching rate required for ERDM. Most relay manufactures only guarantee their relays for up to 10^5 operations, which in this case means the relay could start giving trouble after after a day or so.

      The RF relay used for ERDM must use PIN diodes.

    2. Solid state relay is the only option as far as I can see. I'm checking the part numbers that are on the list at the moment...

      Wayne, you mention using the Vertex EVX Link to get IPSC-like operation. Have you done this? Do you have a design diagram for this? I have an application right now for exactly this sort of system, but I don't have EVX boxes to test with.

      Would one use an EXV box with a control radio at each site, then IP link the EVX boxes? I have to assume that this config would allow only one talk group per control radio, and no data (text, GPS etc)

      I thought that a better option would be to link both ERDM repeaters as "master" repeaters in TRBOnet (ie. two separate systems) and then do a System Bridge through TRBOnet, however TRBOnet has told me that we would require TRBOnet Plus, as well as NAI Data and NAI Voice licenses.

    3. [EDIT]......PIN diodes or any other semiconductor device that allows high speed switching; will not generate intermod and can handle the RF power throughput.

      40009272001 is a RF relay. It can handle the power but cant switch fast enough.

  7. I've checked pricing with Motorola... List price for the parts is:

    0310909E68 SCRTPG,( 2 req’d) USD27.00 each
    30009310002 CABLE, USD21.50 each
    3084921Y21 RF CABLE, USD23.50 each
    40009272001 COAXIAL RELAY, USD461.00 each

    That's the Motorola recommended parts list.

    I've tried looking for Solid State coaxial relays, but have drawn a blank so far...

  8. I've just checked... looks like the relay 40009272001 is electromechanical so it's not suited for ERDM use.

    1. Have a look at:

    2. The Xmicrowave XM-A3N2-0409D SPDT RF Switch (based on the PE42820 from Peregrine) is a ready to use 50W PIN diode switch (just need a metal housing). Unlike most ready to use PIN switches this is affordable. A home brew version would of course be cheaper. The SLR provides a signal to do the switching on its accessory connector.

  9. Thank you Wayne.

    Any comment on creating an IPSC-like system?

  10. Anyone has tried the 50S-1220 4.3 GHz Wide-Band Solid-State Coaxial Switch?
    we contacted motorola but so far they only offered the "EXTENDED RANGE ANTENNA SWITCH KIT mod:PMLN7263A".
    But is only for the srl1000 and slr1000 is only in UHF.

    1. I see one problem: 50S-1220 is only rated for 30dBm (1W). You could turn the power down on the repeater but the switch would still be running full-out. Perhaps the 50S-1268 (same supplier) would be better?

  11. We are working on our first ERDM project at the moment. I'm quite excited to see it "in action" as it were... :)

    1. Very interested as to what antenna system you found successful. Twin antenna or switching.

  12. Can we use ERDM on SLR1000 repeater programmed in Analogue mode?

    1. ERDM is only supported in digital mode. It uses the two time slots which are not applicable in analog mode.

    2. Thanks. The reason I am asking is that we currently have analogue Motorola radios (200+) and a repeater site which consist of a combination of analogue radios and two DR300 repeaters. We currently have coverage issues in our open pit (250M deep) so I was thinking of using the SLR1000 in ERDM just to boost the signal in the pit but the problem is that we are operating in analogue mode. Any bright ideas how i can resolve this?

    3. Hi, This is a complex issue that I have come across before. My problem is that I work for a company that distributes Motorola equipment, so while I can post here on my experiences in my private capacity, as soon as I work on a customer's system it becomes work related, and I don't believe that this blog is the correct forum for this.

      If you PM me, I can perhaps move this conversation off this blog space and advise you further.

    4. Hi Mark can you please give me your e-mail address


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