Uniden MHS335BT handheld: VHF, GPS, DSC and texting!

Ben Stein

Ben Stein

Publisher of Panbo.com, passionate marine electronics enthusiast, completed the Great Loop in 2017.

12 Responses

  1. Jim Hebert says:

    A tip of the hat to Uniden for being the first radio to take advantage of VDSMS.

    I looked into this radio last month and also into the VDSMS provision. For a bit of added information, see


    I believe ITU Recommendation “M.1084-5, Interim solutions for improved efficiency in the use of the band 156-174 MHz by stations in the maritime mobile service,” provides for this service. And the FCC band plan changes made in January 2017 provided allocations for it.



    for more information on allowed channels.

    RTCM 12301.1, “Standard for VHF-FM Digital Small Message Services,
    July 2009” seems to also be applicable.

    • Ben Stein Ben Stein says:

      Thanks Jim,

      I came across your postings while researching my article. I appreciate all the information you provided.

    • Hi Jim,

      I note that the frequency/channel charts on those referenced forum pages contain a LOT of typos – but the USCG “Official” chart at the https://www.navcen.uscg.gov/?pageName=mtVhf page looks pretty clean. As you noted, the USCG apparently made lots of mistakes before they got it right 🙂
      Thanks for all the info! As an aside, I have an Icom M506, and I have the editing software – does anyone know if it can handle a 4-digit channel number/name?

      • Replying to my own comment re: IC-M506. I find that the “new” channels (1021, 1022, etc.) are already there, but turned off – but they can be turned on! Because they are larger numbers, it looks like they will appear at the end of the list, not inline. What I don’t know is if they have the correct frequency info underneath (the software doesn’t show this).
        I’ll be at the boat (& radio) in a week or so – I’ll see how it works then.

  2. Hi Ben,

    Well, I keep finding out how far I am behind the power curve in how the rules are changing – I remember commenting on the FCC’s NPRM on what became VDSMS – seems like yesterday :). Unfortunately, the RTCM 12301.1 is not “freely available” – and I’m not going to invest $20 in finding out what’s in it – and Part 80 doesn’t have anything except the frequencies available. (The RTCM reference above is just to an executive summary, not the Recommendation itself)
    Let’s hope the rules don’t allow SMS use that precludes sharing with voice users – that could get ugly.

    But learning about the new channel numbers is also news, and something we need to be aware of – changing “Channel 22A” to “Channel 1022” is sure to confuse a few folks.. I also see the USCG has a plan for 12.5 kHz interstitial channels – I can’t wait =8^O Now I have to go retype a few interop codeplugs!

    73 DE Hartley

  3. Jim Hebert says:

    I haven’t bought the RTCM recommendation, either.

    If another radio manufacturer follows Uniden with a VDSMS-cable radio, will the two brands inter-operate? One would hope the recommendation for the protocol encouraged that capability.

    • Hi Jim,
      It might – but the “executive summary” pointed to in the article specifically says it’s not an equipment standard.

      I also wonder about the addressing – which is already a big issue for AIS and DCS users – will everyone wanting to use these things be forced – like Ben was – to acquire a multitude of MMSI numbers, one per unit? Is that even legal?

      We live in interesting times.. 🙂


    • Ben Stein Ben Stein says:

      I had, and mostly still have, the same question. I presented that question to Uniden and they were noncommittal about whether it would work. Uniden’s answer seemed to indicate there was enough room in the way the spec is defined to leave room for multiple, incompatible implementations.

      • Hi Ben,

        Doing some thinking – being house-bound today (it’s raining!) I started looking into the MMSI issue, because it’s obvious that if these devices become popular, folks are going to need a separate MMSI for each unit.
        I have an FCC license for Atsa, so I got an MMSI that way – but they’ll only issue one. Yes, it has a trailing zero, but rules that would allow me to change that zero into something else for subsidiary use don’t exist. So I took a look at BoatUS – but their rules are clear – they can only supply you one if you won’t “be communicating with or visiting foreign ports”.
        So I guess I could lie about it and get numbers from BoatUS (I do note they are prepared to issue you multiple numbers!), but this seems more than a bit lame.

        Any thoughts?

        • Ben Stein Ben Stein says:

          My thoughts are that you’re correct that currently there is an issue with MMSIs being issued. One question Ben E. asked me while I was testing these radios was about whether or not I tried them with both radios set to the same MMSI. I didn’t try that and would expect that if I did I might well have seen unpredictable behavior.

          Here’s what I do think. if you have a VDSMS capable radio and your cruising companions also have a VDSMS radio you could all utilize your FCC station license associated MMSI in your radios and the use case would still work. What would be harder is if you owned multiple VDSMS radios and wanted to be able to text among them. This difficulty isn’t new nor is it peculiar to VDSMS use cases. It can also come up with DSC capable (non VDSMS) handhelds as well as instances like dinghy mounted DSC fixed radios.

        • Ben Ellison Ben Ellison says:

          Well, for one thing, don’t presume that you need different MMSI numbers to text from one radio to another. The DSC protocol this texting is related to does not work that way. You can direct dial from one radio to another with the same MMSI, at least in my experience.

          Then again, DSC/GPS/VHF handhelds that will not necessarily live on one boat should be able to have an MMSI associated with a person instead of a boat. As we’ve been discussing since 2013, you included, the global authorities accept that concept and have created a special MMSI config for that use:


          But as I noted in that thread last summer, (the FCC can not produce the needed MMSI blocks without a major expensive software upgrade, so) such numbers are not available in the USA and the CG has suggested workarounds.

          At any rate, according to Ben S, you can now get a handheld MMSI at BoatUS without entering a boat registration or document number, which may be the result of the CG’s tacit acknowledgment of the need.

          • Hi Ben(s),

            True enuff – all you have to do is be prepared to tell them (BoatUS) that you’re not going to any foreign ports and they will issue you a number (or multiple numbers). Whether there are any repercussions if that MMSI turns up elsewhere is not clear.
            I suppose could use the derived “Group MMSI” number, assuming I was willing to have every message going to every unit.
            I could also use my state-registered dinghy instead of Atsa, but the same “foreign port” lie would have to be told.
            As an aside, one of the places I found selling these radios online was also selling 2-packs and 4-packs — no mysteries there!

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