Most interesting to me is the qualification of the GX2400 radio for DSC compliance to ITU-R. M.493-15. This recommendation was publish in January 2019 and is the most recent revision of the recommendation. Most DSC radios being sold in the USA at present are certified to comply with prior revisions of this standard, usually the -13 revision which was published 11 years ago in 2009. At this moment, I believe that the FCC regulations still use ITU-R. M.493-13 as the standard for compliance for DSC radios to be sold in the USA. European DSC radios most likely need a more up-to-date standard for compliance. Because there is a global market for VHF Marine Band radios, and Europe is a large part of that market, it is now common for manufacturers to make radios that can comply with several standards, with the FCC in the USA and the European Union (EU) in Europe being the two biggest markets, and with different standards. I suspect that one significant difference at the moment between FCC and EU regulations is the need in Europe that the radio MUST include an integral GNSS receiver.
Standard-Horizon GX2400 Features:
- two integrated AIS receivers monitoring both AIS channels simultaneously
- second station capability with remote microphone
- integral GPS 66-channel receiver
- noise cancelling on receive and transmit
- integrated voice scrambler with 32 or 4 code
- fog horn
- position plot display for navigation
- although not required for Class-D DSC, this radio adds position polling and position reporting features, normal for Standard-Horizon
- NOAA weather radio receiver with alert monitoring
- wireless remote RAM4W or SSM-71H microphones with optional SCU-30 wireless access point
Dimensions for the front panel are 7.1-inch wide and 3.1-inch high. For flush mounting the cutout dimensions are 6.3-inch wide and 2.5-inch high. I suspect the case size has very likely been made to be compatible with prior models that flush-mounted, so that this GX2400GPS can be a drop in replacement to the existing cut-out. (More research needed to verify this.)
With the fog horn, hailer, and second station features the GX2400 is more suited for larger boats.
The GX2400GPS continues the use of soft-keys, with three keys below the display changing function as indicated by the legends above them. Four input buttons that on some prior models were below the soft-key buttons are now moved to the right of the display. This should improve the user interface by separating the four dedicated-function buttons from the three soft-key or variable function buttons.
There are separate volume, squelch, and on-off buttons and the familiar rotary dial for menu selection with a push-to-select button function integrated with the dial on the far right of the front panel. Dedicated scroll left-right buttons flank the soft-keys. The DSC DISTRESS CALL button is separated from the other controls and contained under a hinged cover on the far left.
Standard-Horizon denotes a new "Group Monitor" function, without much explanation. I presume "Group Monitor" refers to an ability to request position data from a preset list of other boats on at a defined interval, allowing a group of boats traveling together to see each other's position automatically without any operator needing to initiate a DSC call.
The more elaborate than usual voice scrambling feature should be attractive to boaters, particularly commercial fishers, who prefer to have some privacy to their VHF voice radio communication.
The Marine Band receiver is specified as an "80 dB" receiver. This most likely alludes to the receiver's ability to reject intermodulation of two strong local signals. A National Telecommunications and Information Administration (NTIA) study in 1999, "Evaluation of Marine VHF Radios: Compliance to IEC Receiver Standards", studied nine radios available. They found:
Four radios failed the co-channel rejection ratio test and only two radios passed the adjacent channel selectivity test. In most cases the radios which failed were within 3-5 dB of passing the tests. The most important IEC tests, which are related to the complaints about interference in Savannah and New Orleans, were the intermodulation rejection ratio and blocking tests. Four radios passed the intermodulation test while only one passed the blocking test.
While the available literature from Standard-Horizon fails to clarify exactly what performance is being claimed by the designation "80 dB", a reasonable inference is the strong-signal intermodulation rejection or blocking specification required in IEC 1097-7, "Global Maritime Distress and Safety System (GMDSS)-Part 7: Shipborne VHF Radiotelephone Transmitter and Receiver-Operational and Performance Requirements, Methods of Testing and Required Test Results" is being met or exceeded.