Standard-Horizon GX2200

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:08 am

[This is a reprint of an article I wrote about four years ago in the old forum. I am reprinting it here in the VHF MARINE RADIO forum to make it more easily found.--jimh]

Standard-Horizon have announced a new VHF Marine Band radio, the GX2200. This fixed-mount 25-watt Class-D DSC radio also contains a global navigation satellite system receiver for the NAVSTAR GPS and two automatic identification system (AIS) receivers. The GX2200 radio also provides a 30-Watt audio amplifier output for use as a hailer or fog signal generator. The minimum advertise price (MAP) is $400. The new radio will be available in January, 2014.

Image

The VHF Marine Band receiver is described as being a commercial grade receiver with an intermodulation specification of 80-dB. Intermodulation specifications describe how well the receiver can copy a weak signal in the presence of very strong signals on adjacent channels. A rating of 80-dB suggests that the adjacent channel signal must be 80-dB stronger, or 100-million-times stronger, before it affects weak signal reception on the desired channel. This level of receiver intermodulation specification is extremely good. The receiver also has a selectable attenuator for LOCAL or DISTANT reception.

The GX2200 communicates with other devices using the NMEA-0183 protocol. It can combine its AIS and DSC NMEA TALKER data into a single stream for interconnection of chart plotters of other devices that have only a single NMEA LISTENER interface.

The transceiver is compliant with FCC regulations for DSC Class-D rating. In addition to sending DSC emergency broadcasts or setting up DSC voice calls to other vessels, the DSC features can be used to request position information from or send position information to a remote vessel. Standard Horizon was a pioneer in providing these features on their DSC radios.

The radio can listen for NMEA sentences from other devices sending:

    --GLL: geographic position, latitude, longitude
    --GGA: global positioning system fix data
    --GNS: fix data
    --RMC: recommended minimum navigation information
    --GSA: GPS dilution of position and active satellites
    --GSV: satellites in view

and can send to other devices the following NMEA sentences

    --DSC: digital selective calling information
    --DSE: DSC extended
    --VDM: vessel data message wrapper for AIS messages
    --GLL: geographic position, latitude, longitude
    --GGA: global positioning system fix data
    --GNS: fix data
    --RMC: recommended minimum navigation information
    --GSA: GPS dilution of position and active satellites
    --GSV: satellites in view

Note: the radio only sends data from its internal GPS receiver on its NMEA TALKER when the internal GPS receiver has been set to ON. I presume the radio can also only use data from an external GNSS receiver when its internal GPS receiver is set to OFF.

The incorporated global navigation satellite system receiver is described as being a 66-channel receiver with ability to use the space based augmentation system for NAVSTAR GPS known as the Wide Area Augmentation System (WAAS). Position solutions from NAVSTAR GPS with WAAS enhanced precision are typically accurate to about 3-meters. The antenna for the internal receiver appears to be located on the radio front panel. In order to get good reception from satellites in space, the radio will have to be mounted in a location that allows the antenna to have a good view of the sky. On many small boats the radio will be mounted at the helm position on an open deck, so the GPS receiver should work well in that location.

The incorporated AIS receivers shares the antenna connection with the VHF Marine Band transceiver, greatly simplifying installation. The AIS receivers continuously monitor the two AIS channels, except when the radio transmitter is in use. Good integration of the AIS receivers and the VHF Marine Band transceiver permit DSC radio calls to AIS targets to be set up from the radio control panel without having to manually enter the MMSI of the target vessel received by the AIS receivers.

The VHF Marine Band voice receiver can be configured to perform channel scanning in a number of modes. In addition to marine channels, the voice receiver can also tune to NOAA Weather Radio broadcasts, and it will also decode weather alert transmissions it receives and sound an alarm.

The transmitter power is selectable to 25-Watt or 1-Watt. The microphone is a noise-canceling type, and it has a small keypad for selecting channels. An optional voice-scrambler can be installed to encode and decode the voice modulation.

The radio has a large liquid crystal display alpha-numeric display panel which functions as a miniature plotter as well as a user-interface for operation and control of the radio.

The plotter function can display a polar view of AIS target vessels relative to vessel position. When showing AIS targets, the display can present the MMSI, call sign, ship name, bearing, distance, speed over ground, and course over ground of the target vessel. The plotter can also compute the closest point of approach (CPA) and time to closest point of approach (TCPA) of AIS target vessels, and set collision avoidance alarms. The plotter can show bearings in either TRUE or MAGNETIC degrees.

The plotter can also utilize waypoints for navigation. For example, if one stores a waypoint for the entrance to their harbor, the radio could be used as a navigation device to plot a course to that waypoint from seaward, thus providing a back up to the vessel's main electronic navigation devices. As many as 100 waypoints may be stored on the radio. With some thoughtful organization of those waypoints, the radio could be quite an effective alternative navigation system. Note that the NMEA interface does support any sentences which contain waypoint data, so creation of waypoints on the radio's mini-plotter would have to be done using the radio's interface; they could not be generated by a NMEA connection to another plotter.

The display on the GX2200 front panel is also an important part of the user-interface. There are three soft-key buttons below the display. These buttons can be user-programmed to customize the radio menu operation. The user-interface is described with the acronym E2O for Easy To Operate. The display shows the boat's latitude, longitude, course, and speed.

The GX2200 is built on a metal die-cast chassis and is rated for being water submersible to three feet according to IPX-7 specifications. The dimensions are fairly compact: 7.1 W x 3.1 H x 6.3 D in inches.

The GX2200 is sold with a three-year warranty which includes any damage caused by water. After warranty expiration the radio can be repaired for a $65 flat-rate charge.

I always like to plot the position shown on the press photographs of various devices. In the case of the GX2200, the position shown in the photograph of the radio front panel is located about ten mile offshore and south of Long Beach, California. I figure the position shown on the front panel is going to give away the secret location of the research laboratory.

jimh
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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:09 am

A modern marine radio like the Standard-Horizon GX2200 contains a remarkable number of devices. We will use the GX2200 as an example of a modern radio and look more closely at its many components, beginning with the actual radio devices: the radio receivers and radio transmitters. A GX2200 contains five receivers. One is tunable and four are fixed-tuned receivers:
RECEIVERS

Tunable:

    --VHF, tunable to Marine Band or Weather Band; voice; weather band has alert tone decoder

Fixed-tuned:

    --VHF Marine Band Channel 70; digital; digital selective calling (DSC)

    --VHF Marine Band Channel 87B; digital; automatic identification system (ASI-1)

    --VHF Marine Band Channel 88B; digital; automatic identification system (AIS-2)

    --L-band Global Navigation Satellite System (GNSS) receiver for USA's NAVSTAR GPS

The four VHF receivers share the a common antenna and receive continuously, except when a transmitter is operating. The GPS receiver has its own dedicated antenna.

The VHF tunable receiver is tuned to preset frequencies according to a channel band plan. The channel band plan can be set for three different configurations, depending on the location of the radio: USA, Canada, International. The three band plans select which channels can be used. Among the useable channels in the band plan, a scanner function is provided to step the receiver through a pattern of channel scanning. The scanning function halts when the noise squelch circuit is open. The scanning function can be configured to create a variety of scanning patterns, including scanning the weather radio broadcast channels. When scanning a weather radio broadcast channel, the scanning function ignores the carrier squelch stop function on the weather channels; it only stops scanning when a NOAA alert is being received. The scanning function can give priority to certain channels in the scan.

The output of the tunable receiver is the recovered voice modulation of the transmitted signal. The recovered audio is processed by a noise squelch circuit, an audio tone decoder (for NOAA alert tone), and, if present, by an optional voice scrambling decoder. The voice scrambling decode processes the audio to remove the scrambling encoding, restoring the original microphone audio at the transmitter. Note that the voice scramblers at the transmitter and the receiver have to be set for the same encoding/decoding method. The recovered audio is then amplified for use on a loudspeaker. Audio from the loudspeaker is heard by the operator and interpreted by him. If the NOAA weather tone alert is detected, an alarm is sounded.

The fixed-tune receivers monitor their fixed channel continuously; they are not affected by operation of the tunable receiver. The DSC receiver decodes DSC transmissions to their digital message payload. The DSC receiver passes the digital messages to a DSC processor for handling and interpretation. The AIS receivers decode the AIS transmissions to their digital message payload. The AIS receivers pass the digital messages to an AIS processor for handling and interpretation.

The L-band receiver listens for the coarse acquisition carrier of the NAVSTAR GPS satellites. The receiver detects and tracks satellite signals, then processes them into navigation data. The receiver output is a digital message encoded in NMEA-0183 sentences. The output message is passed to the navigation processor in the radio for further handling.

A GX2200 contains two transmitters: One is tunable and the second is fixed tuned:

TRANSMITTERS

Tunable:

    --VHF Marine Band; voice; general communication use

Fixed-tuned

    --VHF Marine Band: digital; digital selective calling (DSC)

The tunable voice transmitter typically follows the tunable voice receiver channel setting, according to the channel band plan in use. On many VHF Marine Band channels the transmitter operates on a frequency offset from the receiver or the transmitter power is limited to 1-Watt. These provisions are incorporated into the channel band plan and are applied to the transmitter. The voice transmitter is modulated from the microphone audio input. The microphone circuit contains a noise-canceling system that works to remove ambient noise from the microphone environment before modulating the transmitter. There is an option for use of a voice-scrambling circuit. If present, the microphone audio is processed before modulating the transmitter. The tunable voice transmitter is controlled by a push-to-talk button. During operation of the tunable voice transmitter, the antenna circuit is switched to the transmitter and all receivers are temporarily disconnected from the antenna.

The fixed-tuned digital transmitter operates on Channel 70. It accepts digital messages from the DSC processor. The digital message is encoded and modulates the transmitter. Typically a DSC transmission is very brief, lasting only a few milliseconds. During operation of the digital transmitter the antenna is switched to the digital transmitter, and all receivers are temporarily disconnected from the antenna.

From the above we see that the device we call "a radio" actually contains seven radio devices: five receivers and two transmitters. These modern marine radios are significantly more complex than the simple receiver-transmitter radios that were in common use just a few years ago.

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:10 am

Let us now look at some of the other circuits included in the "radio" that are not strictly radio-frequency circuits. A good example is the automatic identification system (AIS) circuitry.

The AIS circuitry is provided with the digital data message received by the AIS receiver. These messages are in the form of an NMEA-0183 sentence of type VDM. The data of most NMEA-0183 messages is easily read by a human, as the information is typically transmitted in ASCII text with fields delimited by commas. But the AIS message payload is not easily read, as the message contains a great deal of data that has been pre-coded into a more compact form. This was probably necessary so that the message could be transmitted in a short time interval. Because of the secondary encoding, the NMEA sentence must be passed to a secondary process for additional decoding. To understand this more easily, we look at an example message. The AIS receiver will receive a signal from another boat and demodulate the digital message the other boat was sending as something like this:

!AIVDM,1,1,,A,15O86n001TJ3KutH8ar@<h;l06Hh,0*5D


The first few data elements in the message are easy to read by a human; this example is a AIS message consisting of one fragment, this is the first (and only) fragment, there is no sequential message ID, and the radio channel was the "A" channel or 161.975-MHz. The long string at the end of the message is where most of the actual AIS message payload is sent. This long string has to be decoded into ship and navigation data. The processor decodes this string to produce the real data payload. For our sample message, the transmitted message of "15O86n001TJ3KutH8ar@<h;l06Hh,0*5D" is decoded into:

Message type = 1
Repeat indicator = 0 (no repeat)
User ID (MMSI) = 368183000
Navigational status = 0 (Under way using engine)
Rate of turn = 0.0
Speed over ground = 10.0
Position accuracy = 0 (a default setting, means low accuracy)
Longitude = 83-degrees 8.1154-minutes West
Latitude = 43-degrees 10.7625-minutes North
Course over ground = 5.1-degrees
True heading = 5-degrees
Time stamp = 58
Special maneuver indicator = 0
RAIM-flag = RAIM not in use


As you can see, there was a lot of data encoded into the message sent via the radio. Without further processing of the radio message by the AIS decoder, the AIS message would be of no value. To emphasize this, again, you need much more than an AIS radio to get useful data from AIS. You need to receive the signals, of course, but once you receive the other ship's transmission and demodulate their digital message, that message must be passed on to another process for further decoding before any useful information is obtained. When Standard-Horizon says their GX2200 radio has an AIS receiver, they mean that it has not only a receiver, but the necessary processor to decode the received radio data into useful navigation information. That functionality is usually provided by a chart plotter or a dedicated AIS display plotter. In the Standard-Horizon GX2200, the "radio" provides that function all by itself. This is very useful, as we shall see later when we discuss the radio's LCD display.

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:10 am

Continuing our closer look at the components in a modern marine radio like the GX2200 from Standard Horizon, we will follow the AIS data we mentioned above. We have now received the radio transmission from another vessel sent by its AIS transmitter, the signal was demodulated to the information of the VDM sentence, then the VDM sentence was decoded to extract the navigation data it contained. We now know the MMSI, position, course, and speed of the other vessel. We could gaze at this information in a table, as I have presented it above, but it is still not particularly useful. This data is now passed on to another component of the radio, a navigation computer.

The navigation computer in the radio is aware of the present location of its boat from the navigation data obtained by the GNSS receiver component of radio. It is also aware of the location of the AIS target from the decoding of the VDM message it received. The navigation computer can now calculate the range and bearing from its boat to the target AIS vessel. Before electronic navigation computers, this calculation would be done on a plotting board, or perhaps calculated by some tedious geometric equations. The navigation computer does the calculation in an instant.

In addition, the navigation computer projects the course and speed of both vessels into the future, and calculates how closely the two will approach each other if both maintain their present courses and speeds. This requires repeatedly projecting the course of both vessels into the future on their present tracks, then computing the distance between those two projected positions--a very large number of calculations. By this process, the navigation computer finds the time into the future when the two vessels will be at their closest point of approach. It then computes the range to this point. (It already knows the bearing--it will be on the present course line of its boat.) The navigation computer now tells us the distant ahead to the position where the two vessels will be at their closest point of approach (CPA), if that position is in the future. It also computes the time to reach this point (TCPA) at the present speed. If the courses of the two vessels are not converging, the CPA was in the past, that is, the two vessels are diverging. Again, these calculations are provided almost instantaneously, and update in real time. If the course of the AIS target or the computer's own boat changes, or if either of the speeds change, the CPA and TCPA change accordingly, and these calculations are made nearly instantaneously and are shown on the computer. This data is collision avoidance data, and is very useful for the pilot or master of any vessel to have.

As long as the radio has a navigation computer for computing AIS target CPA and TCPA for collision avoidance, the same computations can be made for any target. Hypothetical targets are called waypoints. The navigation computer can calculated the range and bearing to a waypoint, making navigation to that waypoint very simple. The navigation computer in the GX2200 allows for 100 waypoints to be created and stored. The computer can calculate the course, bearing, and time to go to the waypoint (at the present speed) in an instant.

The navigation computer can also perform similar calculations for the reported position of the target as received from the digital selective calling (DSC) system. We'll look more closely at the DSC system later.

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:11 am

Now that the AIS receiver had received transmissions from other vessels, the AIS decoder has extracted the navigation information from them, and the navigation computer has calculated the range, bearing, CPA, and TCPA, the information is still just available in a listing or table. A modern "radio" like a Standard-Horizon GX2200 takes all of the information to the next step in presentation: a graphical representation of the ship positions on a mini-plotter.

By using the radio's LCD display, a mini-plotter presents a polar diagram of the location of AIS targets relative to the boat's current position. The polar plot shows the range and bearing of AIS targets, indicates their course with a small icon tail, and lists them by Vessel Name or MMSI.

Image
Five AIS target vessels are shown in this mini-plotter display. The legends at the bottom, INFO, CALL, and QUIT, are labels for the softkey buttons below the display. The CH knob scrolls through the list on the right. The selected target is shown in the list by reversed-text, and on the display by the black icon.

Pushing the INFO button produces more information about the AIS target vessel, such as range and bearing to target, CPA, TCPA, and speed and course of the target. The mini-plotter gives an amazing amount of information about the AIS targets and their navigational data relative to the boat. All of this functionality is quite different than what is usually provided on a device we think of as "a radio."

The modern CLASS-D DSC radio with AIS receiver is quite a machine. A modern radio is not just a receiver and transmitter. It is really a navigation computer and digital communication processor wrapped around five receivers and two transmitters. That is more than a radio.

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:12 am

A modern radio contains a digital selective calling feature. Digital selective calling or DSC in a VHF Marine Band fixed-mount radio that is to be sold in the USA is no longer an optional item. FCC regulations require that all VHF Marine Band fixed-mount radios sold or installed on boats in the USA must have DSC features to the Class-D rating. (A complete description of all of the features of a Class-D DSC radio is beyond the scope of this article.) All the elements of being a Class-D DSC radio are accomplished in the radio itself, and are defined in ITU Recommendation M.493. Curiously, that recommendation never mentions the National Marine Electronics Association (NMEA) or any of their standards. However, NMEA has created some standards for communication of data between a DSC radio and other devices.

A Class-D DSC radio will typically be able to communicate information related to digital signal calling to other devices using two NMEA sentences, named DSC and DSE. The NMEA sentence DSC, Digital Selective Calling Information, is used to transfer data to or from a DSC radio. The companion sentence, DSE, Expanded Digital Selective Calling, is a further extension of the data.

In the sentence DSC, the vessel position is to be encoded in a rather unusual method, a result of a format specified in ITU Recommendation M.493. The location is sent as a position with an accuracy of one minute of latitude and longitude, and then augmented with added data to indicate in which of four possible combinations of latitude and longitude (North and East, South and East, North and West, South and West) the actual vessel position lies. This resolution of the position to only one minute gives the vessel location only to an accuracy of about 0.5-nautical miles. That might be good enough to define a position for a large ship in the middle of an ocean, but, in this day and age of position fixes with an accuracy of ten feet, it seems rather anachronistic to report a position with an accuracy of perhaps 3,000-feet.

If a DSC message contains an expansion indicator, then the following sentence is expected to be DSE. The DSE sentence structure allows for sending or receiving more data. This sentence is often used to transmit the exact position of a vessel by just sending its latitude and longitude with greater precision as part of the extended data.

The most common use of data in NMEA sentences from a DSC radio to an external device is to send information to a chart plotter from the radio, giving the location of another vessel. The chart plotter typical responds to this data by plotting the position of the other vessel on a chart display, indicating the identity of the other vessel, and presenting information about the nature of the message that was sent by other other vessel. For an example of this behavior, see an earlier article on that topic at

http://continuouswave.com/ubb/Forum6/HTML/003215.html

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:13 am

By having both an AIS receiver and a DSC transceiver in one unit, Standard-Horizon have provided a very nice solution to initiating a DSC radio call to an AIS target. The radio provides this function all by itself.

Let us suppose we are out trolling for salmon on Lake Michigan late at night, we've fouled a line in the propeller, and we notice from AIS that a large ship is approaching. We might want to call the ship on VHF radio using DSC to make sure they are aware of our boat and our limited ability to maneuver.

Without an integrated system, we can get the MMSI of the ship from the screen of the AIS receiver or its associated plotter. We have to write this data down on a piece of paper. Then, to make a DSC call to that ship, we need to use the DSC radio and enter the MMSI. For most DSC radios used on boats, there is no numeric keypad for entering the long string of digits in an MMSI. The MMSI has to be entered in a rather awkward and cumbrous manner, typically using the rotary knob for the CHANNEL to select the digits. This takes a minute or two and is prone to errors. Typically you might enter the ship's MMSI into your DSC radio's directory, so you could call them a second time in case the first call did not elicit a reply. Then, with the number in the directory, you'd manually set up a DSC call on your radio. This is a tedious process, particularly if the circumstances that prompted you to make a DSC call in the first place are emergent.

With the AIS receiver and DSC transceiver integrated into one radio system as is done on the Standard-Horizon GX2200 AIS, a DSC call to any AIS target can be very quickly and easily initiated. You just select the target vessel from the AIS polar display and use the CALL option. In seconds your DSC radio is calling the AIS target ship's DSC radio.

It is thought to be possible to integrate AIS data and DSC call requests in an external chart plotter. Whether this type of integration will work depends on how the various components interoperate. There is a NMEA-0183 sentence DSI for "DSC Transponder Initialize." The DSI sentence is sent to a DSC radio in order to set up the radio for making a DSC call. However, I do not believe that it is commonplace to have a DSC Class-D radio support this sentence. The GX2200 does not. This means it cannot be set up for a DSC call by an external device. Assuming we found a DSC radio that supported DSI, we would then need a chart plotter or other device that knew how to read the MMSI for a particular ASI target and turn that into a proper DSI sentence. Looking at my HDS-8 first-generation chart plotter as an example, I do not see any support for it to send DSI to another device. (Compare at http://continuouswave.com/ubb/Forum6/HTML/003271.html )

There may be some support for integration of AIS receivers and DSC transceivers in other systems and also by using NMEA-2000 sentences. Typically those integrations are only working if you use devices from the same manufacturer, for example, an all-Garmin system composed of a Garmin radio and a Garmin chart plotter. I haven't actually seen that work myself. I am also very skeptical AIS to DSC call integration would work with devices from different manufacturers.

By providing the DSC Call function as part of the AIS system, Standard-Horizon has made their GX2200 radio easier and simpler to use.

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:13 am

One feature that is not provided in the new Standard-Horizon GX2200 AIS radio is NMEA-2000 connectivity. Among the latest models of VHF Marine Band radios, provision for connection to a NMEA-2000 network has become more common, but this Standard-Horizon radio does not provide it. I am disappointed that Standard-Horizon has not been able to provide NMEA-2000 connectivity in their new radio, but I do not consider the lack of it to be an insurmountable problem.

In most installations on small boats, the VHF Marine Band radio will only be interconnected to one other device, a chart plotter that has an integral GNSS receiver. This connection can be accomplished with an NMEA-0183 serial data connection. Although the details of the wiring and connectors are left to the user to resolve, making such a connection is not excessively difficult, and it is made easier by the generally excellent technical support provided by Standard-Horizon. Their literature usually clearly shows the details of the NMEA-0183 signals, and they often have interconnection diagrams showing all the details of connecting to many popular chart plotters.

Integration of radios and chart plotters that are connected by NMEA-0183 or by NMEA-2000 seems to be still evolving. I am not certain that there is going to be any great loss of features or functionality with the Standard-Horizon GX2200 AIS that will be caused by having only an NMEA-0183 connection. It would be simpler and easier for most boaters to connect the radio to the chart plotter with NMEA-2000, that seems certain, but I do not think such a connection would provide any more functionality than can be obtained with a NMEA-0183 connection. This may not always be true, as we are seeing more instances of manufacturers making both radios and chart plotters, and there may be some crafty and very functional integrations provided when using radios and chart plotters of the same brand. But, for the moment, I don't think the lack of NMEA-2000 is a tragic flaw in the GX2200 AIS. The radio provides many features, and it is priced very competitively.

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Re: Standard-Horizon GX2200

Postby jimh » Sun Jan 14, 2018 11:14 am

Based on the appearance of the GX2200 AIS radio on the website of a large on-line vendor, it appears that the GX2200 AIS has been approved by the FCC and is available for sale. The MSRP of the radio is listed as $666.65, but the minimum advertised price or MAP is $400, which conforms with the initial information I gave in this thread.

[Again, this article and the ones preceding it were written about four years ago. The initial article and the several follow-on articles are reprinted here to make them more accessible from the new forum--jimh]