The Defender catalogue indicates the MRSP of the MDA-4 radio is just $459 and the discounted price is $359.
Among the features of the radio are interfaces for both NMEA-0183 and NMEA-2000. My initial enthusiasm for this was markedly decreased when on further investigation I found that the NMEA-0183 interface appears to be terminated in a connector. The connector is intended for mating to the optional GNSS receiver. A color coding of wires is given, but apparently you'd have to cut off the connector to get to these wires. The manual also seems to ignore any mention of a NMEA-0183 output from the radio such as DSC, DSE, or AIVDM. Without those signals the interface of this radio to a chart plotter would be limited to only via NMEA-2000.
Si-Tex literature calls attention to several characteristics of the radio:
- --Ruggedized to Military Specification (MIL-STD801G*), to stand up to tough conditions and years of hard professional use
--Dual Watch, Tri-Watch and Programmable Scanning Modes
--Robust 25W loud hailer/foghorn with eight selectable modes and listen back
--Optional full-function Remote Command microphone
--Optional 66-channel smart GPS "antenna"
--High-performance dual-channel AIS receiver
I am disappointed that the 12-button keypad layout does NOT appear to be capable of being used for data entry. For example, it would be much easier to enter vessel MMSI data into a directory using a numeric keypad. This feature does not appear to be available on the MDA-4.
It is not clear to me how one selects a radio channel. My best inference is the UP-DWN buttons on the microphone must be used. I much prefer a rotary knob for channel selection.
The provision for an optional GNSS receiver indicates that the radio most likely does not have a built-in or internal GNSS receiver. Also, use of the optional GNSS receiver appears to tie up the NMEA-0183 port for that interface, eliminating it for use with interface to a chart plotter.
Si-Tex is generally not regarded as an actual manufacturer of many of their products; they tend to offer rebranded products made by other electronic companies. This is indeed the case with the MDA-4 radio. The actual manufacturer of the radio is Shenzhen Jiuzhou Himunication Technology Co., Ltd, located in Shenzhen China, who refers to this product with their model designator HM380S. The FCCID for that radio is RIPHM380S. You can find a great deal of information about the radio, its construction, and very thorough testing of its transmitters at the FCC Test Reporting website under that FCCID. (To facilitate searching the FCC website by FCCID I recommend just putting the FCCID into Google; it will quickly locate the FCC test data; I would give a link but it is always sessions based and wouldn't work.) The HM380S was approved in June 2017, so it is a recent design. The FCCID for the SiTex re-branded radio is 2ALU7MDA-4.
The owner's manual is somewhat terse and not extensively illustrated in its explanation of the operation of the radio.
I use the search feature on the website NMEA.ORG to look for a listing of this device as a "certified" NMEA-2000 device. Although I found other Si-Tex products (two) listed as NMEA-2000 certified, I could not find any listing of the MDA-4 radio.
The manufacturer describes the performance of the AIS receiver as "high" but fails to provide any specifications for the receiver. An AIS receiver would typically be specified for sensitivity by citing a particular RF input level necessary to produce digital output in which the modulation has been decoded with a particular bit-error rate percentage. For example, a competitor's radio specifies that the AIS receiver sensitivity is better than -107dBm for a 20-percent packet error rate. In the absence of any sort of specification of the MDA-4 radio's AIS receiver, it is impossible to know how it compares to competitors. The nebulous description of the AIS receiver as "high-performance" means nothing without actual specifications. The notion that it receives dual channels is also not particularly clarifying. The better AIS receivers contain two separate receivers that listen continuously and simultaneously on both channels, decode the data, and buffer it into one output stream. No guidance is given for the MDA-4 AIS receiver to infer if it can do this.