--CLASS D DSC
The two particular radios in this comparison will be the ICOM M-506 and the Standard-Horizon GX6000. ICOM and Standard-Horizon have traditionally been manufacturers that primarily concentrated on radios, and both have a strong reputation in the marine radio market for outstanding radios.
The M-506 has been available for a while. When looking for prices on this radio, the particular version is very important. The radio is available in three tiers: only NMEA-0183; only NMEA-0183 and NMEA-2000; or with NMEA-0183, NMEA-2000, and AIS receiver. All price comparisons must be to the version with all three features, called the M-506-41 model. The MSRP is $990. A typical discount price is $650 from DEFENDER.COM.
( https://www.defender.com/product.jsp?path=-1|344|2028693|2028951&id=2538765 )
The GX6000 radio is just becoming available. I have not seen an MSRP listed. On Amazon the radio is offered by seller "Standard Horizon" (which I presume must be some affiliate of the manufacturer) for $470, but there is currently no stock; I infer that lack of stock is due to the radio's production being just now accelerated following acceptance for sale in the USA.
( https://www.amazon.com/Standard-Horizon-GX6000-Commercial-Grade/dp/B01N9100WL/ref=sr_1_1?ie=UTF8 )
On the basis of those two resellers, the GX6000 has a price advantage of $180 over the M-506.
Based on the literature from the manufacturers or test data, a comparison of features is made; no first-hand information is offered, as I have seen neither radio in person nor tested them on my boat or bench.
The ICOM M-506 radio NMEA-0183 interface is provided on balanced signal pairs, properly indicated as TALKER A/B and LISTENER A/B, and using the proper wire colors:
TALKER A = White
TALKER B = Brown
LISTENER B = Green
LISTENER A = Yellow
INPUT SENTENCES = RMC, GGA, GNS, GLL, VTG
OUTPUT SENTENCES = DSC, DSE
Source: Owner's Manual Page 101
There is no mention of the NMEA sentence VDM, but I would presume that may be an omission in the manual, which is probably written for the base radio version that lacks the AIS receiver.
Unfortunately there is no published owner's manual for the GX6000 radio. Only promotional literature is available. In the Standard-Horizon product catalogue, the GX6000 is noted as providing a NMEA-0183 interface. Inasmuch as Standard-Horizon has previously provided their NMEA-0183 on balanced pairs, and previous models could output DSC, DSE, and VDM sentences, it is assumed this is continued in the GX6000.
The ICOM M-506 gives specific data about NMEA 2000 PGN data, as follows:
Compatible PGN list
059392 ISO Acknowledgement 059392 ISO Acknowledgement
059904 ISO Request 059904 ISO Request
060928 ISO Address Claim 060928 ISO Address Claim
-- 126464 PGN List
126996 Product Information 126996 Product Information
129026 COG-Rapid Update 129026 COG-Rapid Update
129029 GNSS Position Data 129029 GNSS Position Data
-- 129799 Radio Frequency/Mode/Power
-- 129808 DSC Call Information
129038 AIS Class A Position Report 129038 AIS Class A Position Report
129039 AIS Class B Position Report 129039 AIS Class B Position Report
129040 AIS Class B Ext.Pos. Report 129040 AIS Class B Ext.Pos. Report
129041 AIS AtoN Report 129041 AIS AtoN Report
129793 AIS UTC Date Report 129793 AIS UTC Date Report
129794 AIS Class A 129794 AIS Class A
Static and Voyage Static and Voyage
Related Data Related Data
129798 AIS SAR Aircraft 129798 AIS SAR Aircraft
Position Report Position Report
129809 AIS Class B “CS” 129809 AIS Class B “CS”
Static Data Report, Part A Static Data Report, Part A
129810 AIS Class B “CS” 129810 AIS Class B “CS”
Static Data Report, Part B Static Data Report, Part B
Further of note, the NMEA 2000 interface on the ICOM M-506 radio has been certified by NMEA.ORG. Not every product advertising itself as having NMEA-2000 can also claim to have been certified by NMEA.ORG. The M-506 is certainly outstanding in this regard.
There is no specific data available for the Standard-Horizon GX6000 regarding NMEA 2000. This radio will be the first radio manufactured by Standard-Horizon with NMEA 2000 connectivity, and indeed may be the first product of any kind from them with NMEA 2000. For that reason it will be important to learn if their implementation is certified by NMEA, and what PGN datagrams are supported.
Both the M-506 and GX6000 transmitters have been extremely thoroughly tested for and demonstrated compliance with the FCC-required specifications relating to emission power, spurious emissions, and other regulated characteristics of their voice and DSC transmitter. There is little reason to presume one has an advantage over the other. Both are rated as 1-Watt and 25-Watt transmitters for voice calls.
I am not certain the voice receiver in ship radio stations are subject to a particular specification, however, if the radio is approved as a CLASS-D DSC radio, then 47 CFR 80.225 ("Requirements for selective calling equipment") indicates that IEC Standard 62238 must be met. The M-506 rates its voice receiver sensitivity as -13 dBμ for 12 db SINAD. Standard-Horizon rates the GX6000 voice receiver sensitivity as 0.3 μVolt for 12 dB SINAD, or -10.5 dBμVolt. Better receiver sensitivity is indicated by a lower signal level. The ICOM receiver is rated with 75 dB intermodulation rejection ratio; the Standard-Horizon is rated at 80 dB intermodulation rejection ratio. Better intermodulation rejection is indicated by a higher number. Based on these data, the ICOM radio has slightly better sensitivity but slightly worse intermodulation than the Standard-Horizon radio. There are further test specifications for the voice receiver in a DSC CLASS-D radio given in IEC Standard 62238.
DSC Transmitter and Receiver
Because these radios are qualified as DSC CLASS-D radios, their DSC receiver performance must be tested and found in compliance with IEC Standard 62238, "Maritime navigation and radiocommunication equipment and systems - VHF radiotelephone equipment incorporating Class "D" Digital Selective Calling (DSC) - Methods of testing and required test results." In obtaining certification for their radio, ICOM only submitted a statement asserting compliance with that standard. Standard-Horizon submitted extensive test data as conducted by an independent laboratory. A companion article gives more information about DSC Radio Testing.
ICOM specifies the DSC receiver in the M-506 radio has a sensitivity of –5 dBμ emf (typical) (CH70/DSC) (1% BER). This means the receiver can copy and decode a DSC signal with a bit error rate of 0.01 if the radio signal at the 50-Ohm antenna input is 0.28-μVolt.