Uniden MHS335 Handheld Radio with TEXT MESSAGING

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
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Uniden MHS335 Handheld Radio with TEXT MESSAGING

Postby jimh » Tue Apr 24, 2018 2:38 pm

UNIDEN has a VHF Marine Band handheld 6-Watt radio MHS 335 with a very unusual feature: the radio can send text messages to other "VHF text message capable radios." I don't know exactly what that means. One interpretation is that the MHS 335 can send text messages to other Uniden MHS 335 radios, because, as far as I know, this is the only VHF Marine Band DSC radio that offers this feature.

According to the owner's manual, it is possible to address and compose a text message on the MHS 335 radio itself. The process is described in the manual as follows:

  • push the BT SOFT KEY (BT= Bluetooth apparently);
  • select TEXT MESSAGING; a new screen appears with a keyboard and text entry field with the entry cursor in the TO field;
  • enter a stored MMSI number, a new MMSI number, or a stored name from the stored-name directory in the TO field;
  • press NEXT softkey to move entry cursor to message field
  • enter your message text;
  • press NEXT when done;
  • press SEND to send;
  • press EXIT to return to prior mode

Because the Unidn MHS 335 has a Bluetooth interface, you can also use an iOS or Android mobile device, running a Uniden Marine App, to compose and send text message. Communication between the radio and the smartphone apparently occurs via the Bluetooth link.

The smartphone and Bluetooth link and Uniden Marine App can also be used to change settings on the radio to configure it.

This is quite a novel feature for a DSC radio. I infer that the link between radios must be via DSC as the address for the text message is the MMSI of the other "text message capable" radio.

I have not looked at other features of the Uniden MHS 335, but certainly the ability to send text message to other compatible DSC radios and to be able to connect an iOS or Android smartphone via Bluetooth are very distinctive new features in VHF Marine Band Class-D DSC radios.

For more about the radio, visit


The Uniden MHS335 radio carries the FCCID AMDW70001. The same radio is also sold under the model names VHF470B and VHF470G, which are identical in the internal printed circuit boards, electrical circuits, and structure, and differ only in packaging, backlight color, owner's manual, and accessories. The FCC granted approval for sale of this radio in the USA on December 4, 2017.

Posts: 11862
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Re: Uniden MHS335 Handheld Radio with TEXT MESSAGING

Postby jimh » Wed Apr 25, 2018 8:38 am

The feature of the MHS 335 radio that allows text messaging is certainly the most interesting component in the radio, and for the moment I am ignoring its other features to comment further on just the text messaging.

The ability of VHF Marine Band radios to exchange text messages has been mentioned in several regulatory or recommendation documents recently. 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, mentions messaging:

    2.9.2 DSC (1200 bit/s) operation should be used at all times when operating on channel 70. Channel 70 should not be used as a working channel for any purposes. This channel should be kept as an international distress and calling channel. Passing of data for all other purposes such as data messaging, security monitoring, vessel tracking, and automated dependent surveillance (ADS) should be accomplished on another working channel.

The above seems to suggest that DSC methods can be used to make a selective call to another ship station, but the actual transmission of the data for a text message should occur on another channel where data messages are permitted. (See more below for a channel listing.)

Recommendation ITU-R M.1842-1, Characteristics of VHF radio systems and equipment for the exchange of data and electronic mail in the maritime mobile service RR Appendix 18 channels, "describes characteristics of VHF radio systems and equipment used for the exchange of data and electronic mail in the maritime mobile service RR Appendix 18 channels." This document mostly talks about using IP protocols for ship-to-shore message transmission, but for ship-to-ship messaging it does briefly mention:

    6.3 Ship-to-ship
    The VDL protocol should also provide for direct transmission between ships where possible (within radio propagation range) in the simplex ship-ship mode. The duplex ship-shore-ship mode should be used for extended range (beyond the ship-ship radio propagation range).

Further mention of use of text message exchange from ship-to-ship occurs in the FCC's announcement of new VHF Marine Band channel numbers and allowed services. In an earlier article I summarized the channels and uses available for recreational boaters:

06--Intership safety
09--Boater Calling. Commercial and Non-commercial. VDSMS
13--Intership navigation safety. Bridge-to-Bridge
16--International distress, safety, and calling
68--Non-commerical, VDSMS
69--Non-commercial. VDSMS
71--Non-commercial. VDSMS
72--Non-commercial, inter-ship only. VDSMS
1078--Non-commercial. VDSMS
1079--Non-commercial, Great Lakes only. VDSMS
1080--Non-commercial, Great Lakes only. VDSMS

The acronym VDSMS means VHF Digital Small Message Services; read more about VDSMS in the linked article.