Uniden UM725, UM725G, and UM725GBT Radios

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
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Uniden UM725, UM725G, and UM725GBT Radios

Postby jimh » Fri Jun 17, 2022 9:48 am

UNIDEN has introduced three new VHF Marine Band DSC radios with model designators UM725, UM725G, and UM725GBT. While all are CLASS-D DSC radios, and some models include an integral GNSS receiver for the Global Positioning System (GPS) and NMEA-2000 network communication, the most unusual and perhaps innovative feature is the ability to use the recently-authorized VHF Digital Short Message Service (VDSMS) protocol to send short text messages between radios, and having a Bluetooth interface to allow a smartphone to compose the message, available in the top-tier model. UNIDEN asserts that the new UM725GBT is the first fixed-mount 25-Watt VHF Marine Band radio to have VDSMS capability.

Fig. 1. The UNIDEN UM725 VHF Marine Band radio.
UM725.jpg (87.11 KiB) Viewed 5505 times

The base model in the series is the UM725 radio, but it has many excellent features:
  • speaker-microphone handset
  • large LCD screen
  • 16 front panel controls
  • separate volume and squelch controls
  • compliant with latest ITU recommendations ITU-R 493-14, -15, IEC 62238
  • supports remote microphone handset
  • provides NMEA-0183 interface with standard wire insulation colors for interconnection to other devices
  • support for external speaker

The UM725G radio includes all the features of the base radio and adds an internal GNSS receiver for GPS and for augmentation systems WAAS, SBAS, and QZSS. And perhaps most significantly a NMEA-2000 network port is provided. Typically interconnection of the radio to a chart plotter or additional GNSS receiver is greatly simplified by using NMEA-2000 for boaters who plan to self-install the radio.

The UM725GBT radio includes all UM725G features, and adds the VHF Digital Short Message Service (VDSMS) protocol. VDSMS permits the radio to transmit short text messages to other radios with VDSMS capabilities. To improve the user interface to composition and sending of text messages, the UM725GBT adds a Bluetooth interface. By using a smartphone and special application, the text message can be composed on the smartphone using a familiar touchscreen keyboard interface.

The VDSMS protocol is a recent addition to the VHF Marine Band authorization in the USA. This service was authorized in 2016. An earlier article in this forum gives more background on VDSMS. The FCC has already modified the VHF Marine Band frequency allocations (channels) to permit VDSMS operation on several channels. A prior reference article gives details of the [url=VHF Marine Band Channels]recently-changed VHF Marine Band frequencies, channel numbering, and authorized uses[/url].

While the VDSMS protocol and frequencies were authorized several years ago, implementation of these features in VHF Marine Band radios so far is a UNIDEN exclusive. In addition to the new UM725GBT radio, UNIDEN previously released a hand-held VHF Marine Band radio that supported VDSMS, their model MHS335BT.

The UM725 radios comply with the newest ITU recommendations for a Class-D DSC radio, which exceeds the requirement for sale in the USA. This gives the radio the best possible feature set for a Class-D DSC radio, including position polling or position polling reply. More details on url DSC Class-D and position polling are given in a separate article. See

https://continuouswave.com/forum/viewto ... =13&t=6379

The UM725 radio implements the NMEA-0183 protocol and uses the standard wire insulation colors. Unfortunately the technical documentation does not use the correct signal names. The NMEA-0183 interface is provided on a multi-pole connector. A mating connector and short cable with wires at the other engine provide the physical interface.
Use of the standard wire insulation colors by Uniden is a significant advantage compared to other radios whose manufacturers seem to continue to use non-standard wire insulation colors for identification of NMEA-0183 signals, thus unnecessarily confusing users of those radios with regard to making NMEA-0183 interconnection to other devices.


There are 16 front panel controls:
  1. Power ICON
  2. Send DISTRESS Alert
  3. Hi-Lo transmitter power
  4. MENU
  5. CLEAR
  6. Jump to CH 16 or PRIORITY Channel
  7. Volume
  8. Menu cursor up-down or Squech
  9. Push to enter (part of Menu up-down)
  10. Menu cursor left
  11. Menu cursor right
  12. Soft Key left
  13. Soft key center
  14. Soft Key right
  15. Channel change UP
  16. Channel change DOWN
At first glance there appears to be no rotary knob for selecting menu items. The knob at the lower right of the front panel actually provides this function. When the radio is not in what Uniden calls "Standby mode", this knob is rotated to navigate up and down in a menu structure. When the menu choice is highlighted, the knob is pushed to select that option. When the radio returns to "Standby mode", the knob becomes the receiver squelch control. The operator's manual mentions the following modes:
  1. Intercom
  2. North Up
  3. Course Up
  4. Normal Monitoring
  5. Channel
  6. Scan
  7. Navigation
  8. Watch
  9. Favorite Position (GPS)
  10. Marine
Because "Standby mode" is missing in the documentation for modes, I can only guess at the meaning of "Standby mode." It may refer to the radio not being in transmit and not having the receiver un-squelched or "busy."

While all radio transmitters provide a microphone, the UN725 provides a combination speaker and microphone. Having a small speaker in the microphone that can be held close to the operator's ear can be very useful on a small open boat where the radio is being operated in an open cockpit with noise from the engines and hull. The speaker-microphone has these controls:
  • Push to Transmit button
  • Channel Change UP
  • Channel Change DOWN
  • Jump to Ch 16 or Priority channel
While being able to change channels from the speaker-microphone seems like a handy feature, it can also be dangerous. In the process of picking up the microphone to make a transmission, the operator can inadvertently hit a channel change button, causing the radio to switch channels without the operator being aware of what has occurred.

The operator's manual provides a detailed list of the NMEA-2000 parameter groups that the radio can transmit or receive via NMEA-2000.

The large LCD display can provide the status of many radio settings and functions. When not in a special menu selection or other special function mode, the display presents 21-different areas for text or icons to appear to the user. This is an overwhelming amount of data to take in at a glance.

The content of a text message can be composed using an iPhone or Android smartphone application. The smartphone is linked to the UM725GBT radio using Bluetooth communication. Use of a smartphone for composing the text message relieves the sender of having to compose the message on the radio itself and with the radio's user interface controls, which would be more awkward than componsing on a typical smartphone touch screen.

The UNIDEN UM 725-series radios are good examples of the complexity that has been incorporated into modern VHF Marine Band DSC radios. With so many controls, a large screen showing complex displays of text and icons, with comprehensive DSC settings and functions, and with the added VDSMS function, to become familiar with all aspects of this radio will require extensive study and use of the radio.