Cross-digital-mode through hotspot?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K7GAF, Feb 16, 2020.

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  1. K7GAF

    K7GAF XML Subscriber QRZ Page


    I found tons of information on hotspots and there seem to be several MMDVM version out there that can handle D-Star, DMR as well as C4FM. Yet, somehow I can't seem to find a clear answer to the one question that makes or breaks the deal for me:

    Will these multimode hotspots (i e. this MMDVM hotspot) actually translate between the modes or do they just funnel through what goes in?

    In other words, can I use a C4FM radio to talk to the hotspot and have the hotspot forward my signal to a DMR network like Brandmeister? Do I need to use a DMR radio to get onto a distant DMR repeater or con I use a C4FM radio and the hotspot does the conversion?

    Thank You!

    Marco K7GAF
  2. WB2LBV

    WB2LBV Ham Member QRZ Page

    The only hotspots that do this in hardware are the Openspots. OS 1 and 2 can do C4FM-DMR in both directions but not D-Star. The new OS 3 can do cross-mode between all 3.
    The MMDVM Pi-Star hotspots do have C4FM-DMR (not D-Star) cross-mode capability but it's not the same and is done online. I haven't tried it and I don't know how well it works if at all.
    If doing this is important to you then you'll want to pony up for an Openspot. The OS3 is about $300 and there is currently a wait if you order one since they just came out and are being built and shipped in batches.
  3. K7GAF

    K7GAF XML Subscriber QRZ Page

    Thank You, WB2LBV!

    I will read up on those. I am not that much interested in D-Star but I want to get onto the Brandmeister network using my FT-70DR, so C4FM-DMR is all I need.
    This is exactly the information I was looking for. Thank You!

    Marco K7GAF
  4. WB2LBV

    WB2LBV Ham Member QRZ Page

    If you don't care about D-Star then the Openspot 2 may suit your needs. You can still buy a new one from Shark RF for about $200US-
    Or keep an eye out for used ones, they turn up here in the Swapmeet occasionally. Here's a current one (note I have no relationship with the seller, just posting the link as a courtesy)-
    Openspot 1's are discontinued but also can be found used and are a good option if you can use a wired network and don't need wifi.
  5. W4EAE

    W4EAE Premium Subscriber QRZ Page

    It helps to know a little about digital modes.

    D-Star uses one version of AMBE.

    C4FM (DN), NXDN and DMR use a second version of AMBE. They use the same actual audio codec, but in different containers.

    C4FM (WV) and P25 both use the IMBE codec. Again, audio is identical, but container is different.

    So, software on the hotspot can transcode between C4FM(DN)<->DMR<->NXDN with no AMBE chip. This is done by the OpenSpot, the OpenSpot2, and Pi-Star (although it is a lot more clunky in Pi-Star).

    The OpenSpot3 is a different animal. It contains 2 AMBE chips, so it can transcode between AMBE codecs. C4FM(DN)<->DMR<->NXDN<->D-Dstar. What it is actually doing is taking one mode from AMBE to PCM, then from PCM back to AMBE in another mode. Where this excels in comparison to the more limited software method is that audio levels can be adjusted in the transcoding process. With the software container transcoding, you have no access to tweak the audio because the audio is never touched.
    AB6RF, WD9EWK, N8FNR and 2 others like this.
  6. N8FNR

    N8FNR Ham Member QRZ Page

    Do you have an OpenSpot 2? If so could you do a mini-review of it?

    Zack N8FNR
  7. W4EAE

    W4EAE Premium Subscriber QRZ Page

    MMDVM hostspots and the OpenSpot2 pretty much do all of the same things (with a few differences). I will also stress that both work quite well.

    Advantages of the OpenSpot2:

    -Very small, single package product with nothing protruding other than the power supply.
    -More robust and easier to use cross-moding (as described in previous post)
    -A very capable, but much more simple interface than Pi-Star
    -Automatic firmware updates that never get in your way
    -An actual warranty
    -They build it, not you

    I will also add that it is fairly durable. I have dropped it quite a few times, once even opening the case. I just snapped it back together. Because of its small size, I have accidentally left it in my pocket and run it through the washing machine a couple of times. It still works like new ****NOT RECOMMENED**** Since I have quite a few lying around, I ran a Raspberry Pi Zero through the wash. It is now dead--but it only cost me $7.

    Advantages of MMDVM/Pi-Star:

    -D-Star ircddb callsign routing (This doesn't matter if you don't use D-Star, and even though it is the most impressive feature of D-Star, very few people actually use it. (???))
    -It is nice project (if you are into building things)

    Pre-built Pi-Star hotspots are available, but they are all rather dearly priced in my opinion. You could buy an OpenSpot3 for what most of the decent ones cost. The other problem with Pi-Star are the basic quality of the radios used. This isn't a problem for most people; but if you do any serious 70cm work at your station, you don't want a ZumSpot or NanoSpot anywhere near it.

    When it comes down to what you should buy, the biggest question is 'Do you want to tinker (there's nothing wrong with tinkering), or do you want a finished product?' If you want a finished product, the OpenSpot2 (or OpenSpot3 if you desire its enhanced capabilites) is the best value for money.
    WV4M, AB6RF, N8FNR and 1 other person like this.
  8. N8FNR

    N8FNR Ham Member QRZ Page

    Thank you for the great detailed reply! I am leaning towards the Openspot 3 since it is supposed to be so easy to use as you suggest.

    BTW I recently bought an Icom ID-D51a Plus2 and a Anytone AT-D878UV DMR HT.

    Zack N8FNR
    WV4M likes this.
  9. AB6RF

    AB6RF Ham Member QRZ Page

    I would add only one thing to what EAE said above.

    If you are new to the digital voice modes, I'd forget about the cross-modes until you've "mastered" using at least one of the modes directly.
    The digital voice modes are a different animal from the analog modes, and sometimes the learning curve can be steep.
    There are plenty of things to learn in the setup, and also in how to work the modes.

    If you try to go from 0 to cross-mode guru in one leap, it might prove little frustrating (to your self, and to the people who try to help you).
    N8FNR likes this.

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