DMR Cross-band Repeat

Discussion in 'Ham Radio Discussions' started by KC1MUU, May 8, 2020.

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  1. KC1MUU

    KC1MUU Ham Member QRZ Page

    Here is something I have not seen too much info on out there. Using cross-band repeat on DMR using an analog repeater, specifically I have a Kenwood TM V71. Some people say you can, some say you can’t. I tried briefly but didn't seem to have any luck.

    In other words, I am trying to use an HT to cross band repeat my DMR signal to another DMR radio.

    Does anyone have more experience with this?

    Thanks!
     
  2. N1YR

    N1YR Premium Subscriber QRZ Page

    It won't work with an analog radio. DMR uses a four-position frequency shift keying digital modulation data stream. Repeating the sound of the buzz you hear on an analog receiver will not shift the TM-V71's carrier into the appropriate data symbol positions above or below the repeated channel's center frequency.

    Also, don't try to access a DMR repeater through a relay like the TM-V71. The repeater user's radio must receive the timing information from the repeater in order to pulse the transmitter on and off to fit into either the Time Slot 1 or the Time Slot 2 window.
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    You can do it using a Raspberry Pi.

    https://hamvoip.org/

    HAMVOIP
    Asterisk Allstar
    on the Raspberry Pi 2/3/4
     
  4. N1YR

    N1YR Premium Subscriber QRZ Page

    The OP was talking relaying the DMR signal from a handheld through a higher powered radio onto a different band. Repeating recovered analog audio would not do this.

    But something that would be in effect a DMR repeater could be built. The radio or RF section that communicates with the handheld would have to decode the handheld's data, and the radio or RF section that passes it on would have to properly re-encode the data for re-transmission, including receiving slot timing if working a repeater.

    I don't know what the hamvoip Asterisk Allstar device is, but it appears to be one of many internet gateway schemes to create a node or access hot spot at home, or perhaps mobile using cellular data. Would two of these, connected back-to-back on two radios, provide the "no internet" cross-band mobile handheld extender I think the OP was proposing? I don't know, but unless I learn more about them, I expect not.
     
  5. ND5Y

    ND5Y Ham Member QRZ Page

    The AnyTone AT-578UV series are supposed to be capable of DMR/analog same-mode/cross-mode cross band repeat.
     
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    It is basically a very nice repeater controller. It is not necessary to connect it to the internet, But you can.

    There are many users linking DMR to Allstar. To me DMR audio is a bit questionable, Sounding Robotic.
     
  7. KC1MUU

    KC1MUU Ham Member QRZ Page

    Thanks for all the comments, I have learned quite a bit. From what I understand, the DMR information is transmitted slightly above or below the carrier frequency (frequency shift keying). The analog repeater will not incorporate this shift and thus the receiving radio will not be able to decode. Is that about right? Again, this is new to me so I am trying to process everything!

    It is too bad this does not work because that would turn this handheld into quite the powerful unit.
     
  8. N1YR

    N1YR Premium Subscriber QRZ Page

    I think you have it.

    The DMR transmitter modulation is C4FM, a data transmission format which is used by P23, DMR, OpenSky, Yaesu System Fusion, and possibly others.

    There are four frequency positions to shift the FM carrier to. They are a little below channel center, more below center, a little above center, and more above center of the channel. Each position, or symbol, represents 2 bits of data.

    I'm not sure which is which without looking it up, but the binary bit values represented by these symbols are 00, 01, 10, and 11. If the transmit carrier does not stop on time in the correct position for each symbol, no digital information is successfully passed. This could be from attempting to use a transmitter that is not set up to encode the shifts. I have also seen errors from several C4FM transmitters that are so far off frequency that the carriers are bring shifted into data positions that at the far end receiver actually represent different data values than what was intended to be sent.

    C4FM is just a scheme to transfer data. What that data means is different for each format being encoded or decoded. P25, DMR and System Fusion radios can copy each other's data streams, but without the correct software can't understand the meaning of the number streams they copy. It's like copying text in a foreign language, and getting all the letters of the alphabet perfectly, but having no clue what it all means.
     
  9. ND5Y

    ND5Y Ham Member QRZ Page

    DMR (Tier II & III)
    Peak deviation 1.944 kHz
    Symbol Deviation
    01 +3 +1944 Hz
    00 +1 +648 Hz
    10 -1 -648 Hz
    11 -3 -1944 Hz

    NXDN 6.25 kHz (iDAS), dPMR, dPMR446
    Peak deviation 1.05 kHz
    Symbol Deviation
    01 +3 +1050 Hz
    00 +1 +350 Hz
    10 -1 -350 Hz
    11 -3 -1050 Hz

    NXDN 12.5 kHz (NEXEDGE)
    Peak deviation 2.4 kHz
    Symbol Deviation
    01 +3 +2400 Hz
    00 +1 +800 Hz
    10 -1 -800 Hz
    11 -3 -2400 Hz

    APCO P25 Phase I C4FM
    Peak deviation 1.8 kHz
    Symbol Deviation
    01 +3 +1800 Hz
    00 +1 +600 Hz
    10 -1 -600 Hz
    11 -3 -1800 Hz

    Yaesu System Fusion C4FM
    Peak deviation 2.7 kHz
    Symbol Deviation
    01 +3 +2700 Hz
    00 +1 +900 Hz
    10 -1 -900 Hz
    11 -3 -2700 Hz
     
    Last edited: May 12, 2020
    N1YR likes this.
  10. KC1MUU

    KC1MUU Ham Member QRZ Page

    This was phenomenal information, thank you all for taking the time to explain!
     

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