Choosing a first DMR rig: an ignoramus speaks

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This topic contains 2 replies, has 3 voices, and was last updated by 2e0dxo 2e0dxo 2 years, 10 months ago.

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  • #582

    VicS
    VicS

    Participant

    If you are a ham considering purchase of your first DMR rig, congratulations on having selected such an excellent mode. To business:-
    Hand held rigs are a popular first buy. If you intending to operate well within the footprint of a DMR repeater then these might be a good choice. You need to be realistic: your rig will be knocking out around 4w to a rubber duck, most likely at UHF (There are only two VHF DMR repeaters, one at Tring, one at St. Helier).

    UHF can be badly attenuated by trees, weather, buildings and hills so even if you are located well within the footprint of a repeater you may be unlucky and not be able to ‘get in’ to your local repeater. The rule of thumb is that if you can’t see the repeater you can’t talk to it, you need line-of-sight at UHF/VHF!! As an illustration, from my home QTH I can sometimes hear the ‘local’ repeater but I can’t access it. Moving to a point high in the Pennines, I can hit that box from 52 miles away with 4w to a rubber duck: an uninterrupted view of the box is vital.

    If it becomes clear you’re unlucky, you need to be able to unscrew that rubber duck antenna to attach a collinear antenna with substantial gain. The feeder needs to be low loss: if the antenna needs an N-type terminated feed cable, give it one. Don’t use an N-type–>PL259 adapter because they can and do put an swr bump in the feed. On detecting high-ish swr, (1.7:1 can do it) some rigs protect themselves by folding back the output power, making you a lot worse off. In the shack, a short patch lead connecting the handi to the low loss feeder reduces the strain/leverage on the rig antenna connector. Operating from a car is another possibility: a decent mobile antenna on a mag mount can make a great difference to your chances of success.

    Of course, if you bought a rig with a non detachable antenna, you’ve had it. You’re stuck with having to travel to a good spot to operate DMR: sorry about that. Which leads me to another consideration: if you travel a lot, you’re absolutely guaranteed to find yourself in a DMR desert sometimes. So until there’s a DMR box on every other street corner, it is a very smart thing to choose a handi which also does analogue FM & CTCSS so that you can at least work an FM repeater. DMR-only rigs with non detachable antennas are the least flexible solution; undoubtedly they will meet the needs of some (definitely not all) hams.

    Another route to DMR heaven is to go straight to the mobile rig solution. They can whack out much more power, can have excellent, powerful audio and are full of DMR goodness. From my outside-the-fringe area home QTH, 10w to a decent collinear produces an iffy contact with a dmr box 40miles away. 12w, on the other hand nets a solid contact. That’s the wonder of DMR: so long as you can generate a good ‘handshake’ you enjoy perfect Q5 contacts. No gradual deterioration, no degraded signals, just perfect copy until you drop out. In my difficult case, 2w made all the difference: I could go to 25w but why use more power than necessary? -And, of course, you can use mobile rigs …errr… mobile, when 25w might be really useful. I can’t speak for all mobile rigs, but some can certainly handle FM analogue repeaters with CTCSS, which is potentially useful.

    One weird thing to note is that some mobile rigs cost LESS than some handys. More power, good audio, less £££s, what’s not to like?

    OK, that’s the take of an ignoramus on DMR rig acquisition. I’m not going to recommend any particular brands, rigs or dealers: researching what’s available is a major part of the fun. I’m writing as an ageing ham elbowing his way into the switched-on digital world. There are switched on professionals here who can be relied on for solid help: don’t ask me, I don’t know what I’m talking about.


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    #586

    Hax
    Hax

    Keymaster

    Excellent article Vic … Thanks for taking the time to post on MBARS too 🙂


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    #602

    2e0dxo
    2e0dxo

    Keymaster

    Nice post, wish that had been here before i got bullied into DMR 🙂


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