Simrad RS20

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
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Location: Michigan, Lower Peninsula

Simrad RS20

Postby jimh » Wed Apr 18, 2018 12:40 pm

Simrad RS20 VHF Marine Band DSC Class-D radio with NMEA-2000 interface and under $240
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Simrad's RS20 VHF Marine Band radio with DSC Class-D features and both NMEA-0183 and NMEA-2000 interface looks like a very good value. For many years, VHF Marine Band radios tended to have only an NMEA-0183 interface. Recently newer radios have also provided NMEA-2000 interfaces. But often the radios with NMEA-2000 were the top-tier radios in a product line, and had prices of more than $500. Now we have the RS20 radio at a modest price of around $230 with NMEA-2000.

To get a NMEA-2000 interface in other radios, you have to spend:
  • $550 for an ICOM M506
  • $450 for a Standard-Horizon GX6000
  • $370 for a Garmin VHF110
  • $290 for a Raymarine RAY50
(Prices are advertised prices seen on recent searches with GOOGLE SHOPPING; of course, there is always some place selling for less.)

The RS20 retains the NMEA-0183 interface, and provides it with standard wire insulation color coding for the signals. The RS20 listens for NMEA-0183 sentences RMC, GGA, GLL, and GNS, and sends NMEA-0183 sentences DSC and DSE.

Transport of data to a radio from a chart plotter via NMEA-2000 is rather straightforward. Typically the chartplotter will be sending vessel position data to the radio, and not much more. Transport of data to the chart plotter from the radio is more complex. The radio will be sending data to the chartplotter about any DSC calls it receives. Below is a listing of the NMEA-2000 parameter groups by number and description that the radio can either receive from ("RX") the network or send out ("TX") to the network.

PGN   Description        RX TX
59392 ISO Acknowledge x x
59904 ISO Request x x
60928 ISO Address Claim x x
126208 NMEA Grp Func x x
126464 PGN List x
126993 Heartbeat x
126996 Product Info x x
126998 Config Info x
127258 Magnetic Variation x
129026 COG & SOG x
129029 GNSS Position Data x
129044 Datum x
129799 RF/Mode/Power x
129808 DSC Call Info x

Of these PGN's, the most important for interface with a chartplotter are 129029 GNSS Position Data, which can be sent to the radio to give the vessel position, and 129808 DSC Call Information, which the radio will send to a chartplotter. Note that the radio only sends 129808; it does not receive it. This implies you cannot set up a DSC call on the radio by sending 129808 to the radio. Kudos to Simrad for providing the list of PGN's.

Internally the RS20 is identical to the Lowrance LINK-6 radio, except the RS20 provides the NMEA-2000 interface. The LINK-6 sells at a lower price.

Simrad and Lowrance are brands of the NAVICO company. Together they have very long experience with NMEA-2000 interface technology, having been providing it in there many chartplotter products for years. On that basis, I would expect the NMEA-2000 implementation in the Simrad RS20 to be up to the standards of NMEA.

The front panel controls include a large rotary knob control that is used to select the channel tuning of the radio. I much prefer radios that can be tuned by a rotary knob to radios that use a pair of buttons to tune up and down.

The large rotary knob also functions as a selector to choose alphanumeric characters for data entry. The knob is also a pushbutton, and pushing it performs the SELECT function for the menu choice.

The smaller rotary knob is a dual-function control that can be selected to control the audio volume or the squelch threshold. This knob is also a push button, and to toggle between volume and squelch function you push the button. The LCD display shows which function is currently active.

The pushbutton marked with an X is an escape button to jump up a level in the menu structure, to delete the last data entry in a field, and to exit a screen without saving.

The pushbutton with the 0/1 marking is the power control and backlight control. Short presses of the button control the display backlight. Long pushes of the button control the power to the radio.

Another button marked with a rain cloud icon jumps the receiver to the most recently tuned weather broadcast channel.

The button marked SCAN controls scanning functions, with short and long presses giving different options. The TRI button also affects receiver scanning. These scanning features are complex, and users will probably have to carefully study the owner's guide to become masters of all the options.

The button marked 16/9 toggles between Channels 16 and 9 or a user-designated priority channel.

The red EMERG button is actually a cover that must be lifted to reveal a hidden button. The hidden button is the DSC DISTRESS ALERT call initiation button. A short press leads to a menu where the NATURE OF DISTRESS can be selected. A long press sends a DISTRESS ALERT with NATURE OF DISTRESS set to unspecified.

Consult the user manual for more explanations of the control functions.

The LCD display show about 15 different fields of icons that convey particular status information to the operator. The installation instructions properly note that the operator's viewing angle to the LCD display should be limited to not more than 20-degrees off axis in either horizontal or vertical.

The handheld microphone has unusual shape; it looks like it was designed for use in a Star Wars movie. The microphone has five buttons:
  • Push to talk
  • H/L power toggle
  • + to change channel upward
  • - to change channel downward
  • 16/9 to jump to 16 or 9 or priority channel
The microphone is attached to the main chassis, is not removable, and exits forward from the front panel.

The RS20 can be configured for various VHF Marine Band channel assignment plans, including for the USA, for Canada, and for International waters. For use in Europe the radio also supports the automatic transmitter identification system (ATIS) mandated for use on inland waterways. A separate article explains more about ATIS.