Standard Horizon GX6500: a loaded VHF radio also integrated with Class B AIS

... written for Panbo by Ben Ellison and posted on Oct 11, 2016


The wait is almost over. The Standard Horizon Quantum GX6500 combines Class B AIS and VHF transceivers into one device, an important first in critical marine communications that some boaters have long hoped for. It is not yet for sale pending FCC approval, but the expected price of $800 seems quite reasonable given the install efficiency, the integrated GPS/VHF/AIS features, and a lot more that Standard has designed in. The GX6500 would be an extraordinary radio even without the AIS...

Standard_Horizon_Quantum_GX6500_VHF_radio_and_Class_B_AIS_closeup_aPanbo.jpgI briefly got my fingers on a prototype GX6500 at the NMEA Conference, and the interface to its many features seemed completely up to the task. I don't have dimensions yet, but that's a huge display, and note both the soft key row and the up/down, left/right key column for getting around the menu systems, which are often usefully graphic, plus the knobs for common adjustments.

So that interface accesses an "advanced 80 dB commercial grade" Class D VHF as well as a full Class B AIS with its own target display and CPA/TCPA alarm system. Plus, since it has its own GPS, it can also display COG/SOG and manage waypoints. But here's what else: a dual zone 25W PA / hailer with programmed fog signals and listen back, a voice recorder able to play back two minutes of receive audio, and two types of voice scrambling. And while all that is available just from the single standalone device...

Standard_Horizon_Quantum_GX6500_VHF_radio_and_Class_B_AIS_backside_cPanbo.jpg...the Quantum GX6500 also offers AIS and DSC info integration with navigation systems over both NMEA 0183 and 2000 and -- holy cow -- up to five wired and wireless full-featured remote mics. The two upper right RAM ports handle all those mics, as will be explained shortly, and the bottom ports go like this: one for the plug-and-play 66 channel WAAS GPS antenna, one as an alternate attachment point for the hand mic (with a 20-foot extension cable available), and the standard N2K port (Standard's first on a VHF, but probably just the beginning).

But, yes, the GX6500 does require two antennas, one for the VHF and one for the AIS (preferably an AIS specific model, though a regular VHF stick will work). In other words, it does not contain an internal splitter, which does make installation more difficult and expensive, but it is also arguably the high-performance pro way to go. In fact, the dual antenna requirement also applies to the AIS-receive-only GX6000 model, which will have all the other features of the 6500 and will cost $500 once it's been FCC approved.

Standard_Horizon_SCU-31_GPS_n_SCU-30_wireless_access_point_aPanbo.jpgAt left above is Standard's new SCU-31 GPS Smart Antenna, which is included with the GX6500 but will also be available as a $120 option for the GX6000, thus making it a standalone DSC VHF and AIS plotter if and when you want it to be. To the right is the SCU-30 Wireless Access Point that can connect either new VHF/AIS (via one of its RAM ports) to as many as four RAM4W wireless mics with a range of about 65 feet from the antenna. The RAM4W is shown alongside the RAM4 wired mic below and each of these three optional components will cost $150. It will add up, but a boat could have six Quantum GX stations -- one wired RAM, four wireless, and the base.

However many stations you have, all will have full control of the base, including AIS displays, intercom ability from any one to another or to all, and even an MOB function. The wireless RAM has USB charging to an 1800Ah Li-ion batter purportedly able to provide "up to 14 hours of use", and it not only floats but has the water-activated emergency strobe light seen on Standard's recent handhelds. It even has programmable hot keys for, say, quick access to that intercom function.

So did Standard Horizon leave anything out? The only missing feature I can think of is the numeric keyboard that some pros like, but with either the GX6000 or 6500 you won't have to key in an MMSI to direct call an AIS target. And the 6500 will only have to be set up once with its own MMSI to have both DSC VHF and AIS, either standalone with a single efficient power source (like perhaps when anchored) or data integrated with your underway nav electronics.

This is a first glimpse, and further detail on these new products isn't online yet, but I tentatively applaud Standard Horizon for designing a terrifically full-featured and flexible VHF/AIS combination system at fair prices. I can particularly picture the GX6500 as a valuable communications and safety tool on vessels both small and large. Now what do you all think?


PS: Here's a dimensional drawing of the new radios:



Did they leave anything out? Yes the internal antenna splitter. Would be great if there were two antenna connections with the option of using one with an internal splitter.

I hope this is the first of many, seems odd to me that all VHF-AIS combinations so far have been RX only for AIS.

Posted by: Hugh Saunders at October 11, 2016 12:08 PM | Reply

Hugh, I think it's quite hard to build a VHF / Class B AIS combo device that meets two separate and rigid specifications. It may not even be legal to build one with an antenna splitter inside. I don't believe it's possible, for instance, to receive AIS signals if you are transmitting through the same antenna at 25 Watts.

Standard Horizon was already first to combine a fixed VHF with an AIS receiver, but that's a significantly different animal because AIS receivers are not regulated. There are many such combos available now and all use a single VHF antenna, so I'd call the GX6000 the high performance version of VHF / RX only AIS designs.

Posted by: Ben in reply to Hugh Saunders at October 11, 2016 12:22 PM | Reply

I like wireless mics. I wish EVERY VHF manufacturer offered this feature.

Thus far I am only aware of the Garmin VHF 300 and now this Standard Horizon model.

Posted by: Anonymous at October 11, 2016 12:43 PM | Reply

I wish this had come out a couple of months ago as it might have saved me $600 for a Class B AIS transponder! Great that someone has finally cracked this barrier as it should significantly increase the number of AIS equipped boats through a simpler, cheaper installation.

I wonder about Ben's comment on antenna splitters. I have a Digital Yacht AIT2000 transponder and their SPL2000 splitter, which I use to share a single VHF antenna with a Standard Horizon GX5500S. I have never noticed any disruption in the AIS when transmitting on the VHF. Probably the data transmission and receiving intervals on the Class B AIS are such that they can use a relay to isolate the VHF during the typical relatively brief VHF transmissions without creating any visible impact.

Posted by: Quitsa at October 11, 2016 2:39 PM | Reply

The Simrad/B&G radios have use wireless handsets for years.

Posted by: Anonymous in reply to Anonymous at October 11, 2016 2:44 PM | Reply

Sounds pretty complete, is there a "Stealth" mode for the AIS Xmit?

For those of us who race inshore it's a nice feature to be able to selectively turn off, without having to shut off the receive. With a separate AIS Xceiver, worst case can shut it down, and use the integrated AIS receiver in a VHF.

Using an external splitter should be no issue, just need some low loss short cables to plumb it all together, and you get AM/FM for entertainment on the side.

Regarding wireless microphones, Navico has the H50 for B&G (Simrad has same with different model#)

Handy to have at the helm, or in your pocket as you attend to tasks away from the radio's installation and still retain the 25 Watts and 50' antenna.

Posted by: Sheldon Haynie at October 11, 2016 2:48 PM | Reply

Looks very slick. I wonder if they will sell headsets or even better, in-ears.

We had a Eartec Simultalks for anchor/docking duty but after about two years the audio jack on one of them broke and as the units are sealed we haven't yet found a shop willing to crack ours open and fix it. I am certainly not buying another pricy unit!

So, we end up using our two B&G H50 wireless handsets on intercom mode. The downside is that the headset jack is so absolutely non-standard, the Navico 1-800 guys did not even know it was there, and it took another thread on this website for a reader to post the mic wiring schema. In any event, it seems one would only get Rx, not Tx, so, custom work for scanty return. I just know one of these days I'm going to drop an H50 in the water as I am doing anchor work.

Prospective GX6500 wireless mic buyers should inquire about potential software upgrades. Our B&G wireless mics cannot be updated by the user and must instead be sent to Navico or a specialised dealer —and you can't update the base radio unless you update the mics. We did this already once this year and a couple of months later B&G put out another update that requires again sending the mics to Navico.... hopefully Standard Horizon has a better strategy!

Posted by: Xavier Itzmann at October 11, 2016 3:36 PM | Reply

I have been using a Simrad VHF for 2 years with NMEA2000 and AIS Receive. It also has wireless mike. Another option very affordable.

Posted by: John Miller, Dulcinea at October 12, 2016 9:52 AM | Reply

I dont agree that the trend for combining different functions into one is the right solution. Let us not forget that a failure on a combined VHF and AIS will render both useless.Also the price estimated is not that economic if we look at seperate units. You can purchase a good quality fixed VHF for around the 250 USD and Class B AIS for 500-600. Installation time will be reduced with a combined set. We must consider vessel specifics i.e. I do see a combined unit favored on a Super Yacht Tender, or as a backup second or third station.

Posted by: mvmsystem at October 12, 2016 2:32 PM | Reply

Sheldon, the GX6500 does have Silent Mode, which is the term for turning off TX while retaining RX and may be part of the Class B spec.

I'm still long testing the RS35 VHF & HS35 wireless handset on Gizmo -- used them today -- and while some users had issues with the radio, I think they were eventually fixed with updates and I remain a fan of the handset particularly:

But I think this new SH Quantum is at a different level. MVMsytem, I won't argue about the possible value of independent devices, but I challenge you to show us a VHF of this quality and feature set for $250.

Posted by: Ben at October 12, 2016 8:45 PM | Reply

I am optimistic the combined unit is going to offer a far more reliable red rescue 21 emergrncy button function during the life of a boat than the individual parts integrated together.

To know that if you fall in the water or are very sick your crew can push the button to xmit location to summon help, is a valuable 1st line safety opportunity to get local help heading your way.

Posted by: Dan Corcoran (b393capt) at October 12, 2016 9:04 PM | Reply

Here are the dimensions of the GX6500 and 6000 base units:

OVERALL: 6.9” wide x 4.3” high x 7.6” deep (overall depth includes the front knobs)

CUT OUT: 6.1” wide x 3.6” high x 5.8” deep

I also just posted a dimensional drawing at the end of the entry, and according to a dealer/poster at The Hull Truth, this all means that the radios have "the exact same footprint of the ICOM 504 / 506":

Speaking of ICOM, most of their DSC radios are shipping again in the USA, after being fixed to correct some fairly minor software issues as demanded by the FCC. However, the 604 VHF and the 802 SSB can not fixed and will not be offered again in the US, replacements coming. More detail in the comments here:

Posted by: Ben at October 13, 2016 9:37 AM | Reply

FWIW this setup is 100% legal in Europe / Germany: Icom 506 via active splitter built into a Class B transponder to share one antenna. All modes possible TX off etc.

Posted by: jan at October 13, 2016 2:06 PM | Reply

Thanks, Jan. The Garmin AIS 600 Class B AIS also has a built-in "active" antenna splitter and is FCC approved, but I'm thinking that the FCC might not like to see that inside a VHF.

But regardless of the regulations, don't you think that having a dedicated antenna for each task is ideal when possible? Am I not correct that a single VHF antenna can not receive anything when it's being used to transmit VHF (though most of us don't actually key the transmit button very much)?

Posted by: Ben in reply to jan at October 13, 2016 7:32 PM | Reply

Thanks and agreed, Ben.
The setup I mentioned is installed on a 30ft classic sailing boat...if space and "visual tech-clutter " is no issue I'd also vote for 100% redundant setups, three antennas in best case, two mounted VHF's and one AIS ore two internal AIS transponders, external GPS... etc...and Class A AIS in best case... BTW really liked the discussions on here about A vs B.
Class B protocol means for AIS TX to wait anyway until there's no Class A traffic on the channel...and there are also delays with AIS RX when VHF is in TX, absolutely.

School of thought with the unit in discussion is to put several eggs into one basket, so I'd also want internal splitter when going down that route.
Two VHF's come in handy anyway, so how about two of those combo's with splitter...and two antennas instead of four :-)

If FCC begs to differ between splitter in AIS B transponders vs splitter in VHF AIS combos, would be nice to hear why, me a s dummy enduser can't see much difference.

As a sidenote,
we also opted to add independant IOCM 91 to the setup on said classic boat, RX /TX is much better than expected from a handheld,
we also have an adapter to use better external mobile antennas on the 91.

Good to have those AIS / VHF tranceivers popping up, I'm looking forward for more choices.


Posted by: Jan at October 14, 2016 4:00 AM | Reply

Thanks for another great article Ben,
This gives me a chance to ask why Furuno VHF radios receive so little attention. Seems like their FM-4721 model builds on Furuno's reputation of solid long term investments, yet you can't find any reviews and hardly more than a brochure describing features. For those of us who don't need/want a VHF with AIS, and given that iCom's top end M604A is dead, the FM-4721 seems to bring a feature rich radio. Good alternative?

Posted by: Bo Collier at October 15, 2016 9:24 AM | Reply

Bo, I don't believe the Furuno 4721 is available in the USA. Furuno only sells an IMO compliant VHF radio in the United States which has an MSRP of $2500. The Furuno FM8900S is the only VHF radio shown on the US website

Posted by: Howard in reply to Bo Collier at October 15, 2016 11:29 AM | Reply

Thanks Howard, I guess that explains why you can't find any resellers. But the 4721 is in their 2016 catalog without any mention of not available in the US. I appreciate the info.

Posted by: Bo Collier at October 15, 2016 1:10 PM | Reply

"I don't believe it's possible, for instance, to receive AIS signals if you are transmitting through the same antenna at 25 Watts."

Pretty sure it's possible, seeing as my Standard Horizon GX2200 does it.

Posted by: Robert Carpenter Shook in reply to Ben at October 17, 2016 4:52 PM | Reply

It's likely your setup alternates use of a common antenna, it's less likely that you are concurrently transmitting at 25 watts and sending/receiving AIS.

Posted by: Sheldon Haynie at October 17, 2016 5:03 PM | Reply

Robert, the only way you could tell for sure is to hold down the transmit button on the GX2200 -- or any other VHF sharing an antenna with AIS RX -- for quite a long time. AIS target displays are quite generous about data reception largely because Class B only transmits every 30 seconds at best. It seems to vary from display to display but I think that AIS targets often linger for several minutes after last data reception before the display marks them as invalid or just erases them.

At any rate, I just don't think that a coax cable and VHF antenna can receive anything while 25 Watts of transmission are going the other way.

Posted by: Ben at October 17, 2016 5:55 PM | Reply

Antennas can be used to simultaneously transmit and receive however a complicated and expensive filter called a duplexer must be used. There may also be a digital way of time sharing the transmit and receive information but I believe both of these technologies are beyond the expense of a recreational marine radio. So part of the information will be sometimes missed unless a two antenna system is used. I haven't read through the entire thread but I don't believe that a shared antenna would be preferred in a high density (lots of transmissions) area.

Posted by: Florida Marine Surveyor - Latitude Marine Inc. at October 17, 2016 6:19 PM | Reply

The manual for my Digital Yacht splitter specifically notes "It is not possible for both connected devices to transmit simultaneously using a single VHF antenna. Whilst you are talking on your VHF Radiotelephone no AIS position reports will be transmitted." The manual also makes clear that the antenna is shared unless the VHF or AIS is transmitting, in which case it is switched exclusively to that unit. So both can receive simultaneously but if one transmits, the other is temporarily disconnected from the antenna and can neither receive nor transmit.

Posted by: Quitsa at October 18, 2016 1:34 PM | Reply

Thanks, Quitsa. I haven't noticed it myself, but some boaters using antenna splitters say they can hear a little click when they're listening to something on VHF and the AIS cuts in for a few nano seconds to make a transmission.

So while using a single antenna for VHF and AIS is a bit of a compromise, I don't see any technical compromise to combining AIS and VHF transceivers like the GX6500 does.

Posted by: Ben at October 18, 2016 5:56 PM | Reply

My concern, albeit mild one is when using one of those transmit antenna combiners is that the radios are not coordinated. Both theoretically can transmit at one time, but one is not connected to the antenna.

The radio that is temporarily not connected to the antenna is transmitting into? Is it a 50ohm load that dissipates the RF energy? Or is just an electrical short/open?

Anybody open one up?

Posted by: Howard in reply to Ben at October 18, 2016 6:07 PM | Reply

Howard, I've been long testing a Vesper Marine VHF/AIS/FM splitter for years and have yet to see any problems. In fact, I A/B tested it and could not see any difference in the number or range of targets received (another worry being signal loss):

I believe that the main job of such "active" splitters is to protect each transceiver from RF damage.

Posted by: Ben in reply to Howard at October 18, 2016 7:33 PM | Reply

My experience with the Digital Yacht SPL-2000 is the same. One reason I am not especially concerned with the small interruptions is that I have two VHFs and two antennas. The AIS shares an antenna with my backup VHF. Thus normally I am transmitting on VHF from the radio that has a dedicated antenna and the AIS transponder is not affected whether receiving or transmitting. I have done an "A/B" test with my two VHF radios using a shore "test" station and the one with the splitter seems to have just as much range as the one with its own antenna. I think this is a good setup for people who are not going for the Gizmo antenna forest look and have two VHFs on board.

In my case the splitter allows me to have two antennas instead of three and the AIS benefits from being connected to a 17' antenna mounted on the hardtop, which gives it pretty incredible range for Class A transponders on large ships. I regularly see AIS targets on my plotter that are 35-40+ miles away (not that it matters much to have that range). Other people with similar antenna height have reported that they picked up my AIS over 12 miles away, which has to be about as good as Class B can achieve.

Posted by: Quitsa at October 19, 2016 2:12 AM | Reply

The ORC class rules specify, and I quote:

3.29.13 an AIS Transponder which either:
a) shares the masthead VHF antenna via a low loss AIS antenna splitter; or
b) has a dedicated AIS antenna not less than 38 cm (15”) in length mounted with
its base not less than 3 m (10’) above the Waterline and co-axial feeder cable
with not more than 40% power loss (Loss Estimator)

My AIS range went up considerably when I moved from the dedicated AIS antenna (at about 4 m above sea level) to a shared masthead antenna (at 29 m), both in how far away I am seen and how far I can see myself.

Posted by: Kees at October 19, 2016 8:42 AM | Reply

Ben, I agree - it is not possible for the AIS receiver to hear anything while the 25w VHF transmitter is on when using the same antenna - without large & complex duplexing filters, anyway. But it is also true that unless your VHF and AIS antennas are separated by a large distance (more distance than is available on most cruising boats IMHO), the AIS receive performance will be degraded when you are transmitting on the main VHF anyway.
I'd be quite surprised if the various "splitters" didn't terminate the AIS into a dummy load when the main VHF is transmitting - it would be easy to do, and the amount of power being dissipated is trivial. The 30 millisecond dropout experienced by the main VHF receiver when the AIS transmits would be barely audible. I've occasionally heard a "pop" while receiving (I use a separate AIS antenna) that I attribute to the AIS transmitting and desensing the receiver - but it is very subtle.

The dimensions given for the GX6000/6500 are quite close to the IC-506 - EXCEPT the depth, which is 4.09 inches for the Icom. As you know, I have my helm VHF in a console box, so depth is a big concern for me. I have been unhappy with the receiver performance of the GX1600 I have, and I've been looking at alternates.

Posted by: Hartley in reply to Ben at October 22, 2016 10:26 AM | Reply

Yo, Bo! I understand that the Furuno FM-4721 is built by Standard Horizon and quite a bit like the GX5500:

Posted by: Ben in reply to Bo Collier at October 26, 2016 4:51 PM | Reply

Thanks Ben,
Wow, the SH GX5500 is the Furuno FM-4712 with the keypad and display flipped. I guess when you look at who makes Standard Horizon it makes sense. Maybe I'm old fashioned but I prefer a VHF with a keypad and about the only thing other than the channel number I want cluttering my display is GPS position. Looks like the GX5500 has been around since about 2009 but I'm going to pull the trigger and buy two for our newly redesigned helm and try and sell the one iCom 604A (still in the box) since a second matching one is no longer available. ICom may have really shot themselves in the foot by not being able to resolve their M604A FCC issue.
Once again, thanks for sharing your vast knowledge.

Posted by: Anonymous in reply to Ben at October 28, 2016 9:05 AM | Reply

I would not hesitate to get a GX5500 having used one for five years. It has excellent performance and if you don't need new the features in the GX6500, should work just fine. I put one in my new boat a couple of months ago in fact.

I would bet the basic VHF circuits are not really much changed -- specifications are identical.

Posted by: Quitsa in reply to Anonymous at October 29, 2016 4:18 AM | Reply

GX6500 looks very interesting. I have to replace a AIS transceiver and VHF after a lightning strike. Any ideas how long the FCC approval might take?

Posted by: Cmonster at October 31, 2016 6:10 PM | Reply

The filtering required to have one port / one antenna would be large, and potentially need periodic adjustments to keep it in tune. I'd fear a good knock from a storm could get the filter out of tune.

A two way radio shop could add the filters necessary to accomplish this. Size would depend which VHF channels you want to keep. Channel 16 is > 5 MHz separation from AIS frequencies. An $80 duplexer from China via ebay will give you that separation. They're about the same size as the radio itself, maybe a bit smaller. Channel 88 is only 4.5 MHz which becomes more difficult. 84, 85, and 86 are duplex, and will be very difficult. Now we're talking about a diplexor that is not practical. Probably the size of 6 medium size fenders for a 30' boat.

Posted by: k8md at November 5, 2016 9:02 AM | Reply

Love it! Finally everything I want in one package.

Posted by: Singularity at November 5, 2016 5:13 PM | Reply

Besides the missing internal antenna splitter, I am disappointed to see they opted for a smart GPS antenna instead of a coax fed antenna, like nearly everyone else. The advantage of a coax fed antenna is we have a variety of antennas to choose from to suit the vessel, we can easily cut the cable to length and in the case where we have multiple coax fed GPS devices, we can share the antenna signal and reduce our antenna count.

I look forward to a less feature rich version (e.g. no hailer) and a smaller and lighter package, just 'cuz it will fit our clients better.

Any idea of standby current consumption?

Posted by: emsusa at November 7, 2016 11:32 AM | Reply

How soon? I do not see any FCC application pending for this radio.

Posted by: Waterman at November 12, 2016 4:58 PM | Reply

From a reliable source on Nov 6th:

"Thank you for contacting Standard Horizon, the GX6500/6000 is still pending FCC approval. We hope to begin shipping in late December."

Posted by: Singularity at November 16, 2016 10:32 PM | Reply

Very interesting, indeed. I'm the happy owner of not only a SH GX2200 (receive-only AIS), but I even bought the loudhailer and the remote mic (it's in a pilothouse with an outside helm). I'm not sure if I would go for this right away, but I'm hoping it will lower the price of Vesper and Digital Yacht's similar transceivers, because it certainly hits a sweet spot for those wanting both to be see and be seen via both radar and AIS.

Posted by: Marc Dacey at November 20, 2016 11:26 PM | Reply

Remember, Furuno's small boat VHFs are typically manufactured by a subcontractor. The 3724 is actually a Vertex/Standard radio.

Posted by: Anonymous in reply to Bo Collier at December 14, 2016 9:16 AM | Reply

Icom UK has announced a new M605EURO model that has many of the high end features SH designed into the (AIS rx only) GX6000, plus a beautiful color screen:

Posted by: Ben at December 22, 2016 10:29 AM | Reply

Did they leave anything out? Unless I missed it - WIFI to connect AIS to Tablet Plotter Apps

Posted by: Monty at January 7, 2017 6:44 AM | Reply

Now showing in their 2017 catalog. Interesting that they label it commercial

Posted by: Howard at January 16, 2017 11:30 PM | Reply

I really wish it operated with one antenna as well.

We have the matrix now with ais receive only, with the antenna on the masthead with low loss cable up the mast. Receives big ships out to 70 miles. How are the antenna ports set up? Is one port vhf tx and receive? And the other port is ais rx and tx?

In my situation, it would be ideal to use it like the matrix, using the masthead antenna for vhf/ais receive. And the second port for ais tx on a deck mounted antenna.

But would bet the radio is set up as 1 port vhf other port ais.

Posted by: Louie at February 2, 2017 10:02 AM | Reply

Putting an AIS on the stern rail is a good option. You can use an antenna better tuned to AIS, the install is usually a DIY cable run (use a deck gland), and although you lose range vs masthead the range is still good with the taller commerical vessels.

Posted by: Dan Corcoran (b393capt) at February 3, 2017 1:36 PM | Reply

Reading this and not finding any more specific info else ware on the Internet i wonder about why it is called "commercial grade" and class D. I would think a commercial grade would be an class A gmdss vhf. Then it would also dictate 2 antennas anyway as a "class A" vhf uses the one for listening on DSC channel 70. Modern receivers can easily listen on several freq simultaneously, and similar can signal be modulated on several freq before it is amplified so maybe the one receives and the other transmits for both functions (AIS and VHF). Placing 2 antennas inline vertically also give less interference. Anyone have a pointer to a manual or more specific data ?

Posted by: Johan at February 24, 2017 8:20 PM | Reply

I'm all about reduced wiring, complexity, and ease of installation. So after initial excitement about its integrated AIS I am left disappointed by the GX6500.

1) Why didn't they integrate the GPS as several radios already do? Or make GPS attainable via an existing GPS on your N2K network? There should be no need for yet another separate GPS antenna.

2) Not having an internal splitter is a show stopper. Having to use a separate external splitter box or separate external antenna to me almost defeats the goal of the AIS integration. Briefly not being able to receive AIS while your keying the mic is more than overcome by the much better range performance of a mast head mounted shared VHF antenna (sailboater here)!

Strip out some of the other bells and whistles and give me the priorities above, and I would pay double the $800USD they want for this.

The good news is someone else should be close to offering the above soon. I'm always willingly to pay more for less.

Posted by: Anonymous at March 2, 2017 10:48 AM | Reply

Well, anon, you'll never see an AIS transponder that can use an external GPS source because it is not permitted. It is possible for a Class B to output fully valid and fast GPS info over NMEA 2000 (not 0183, not enough room), but so far only Vesper Marine does this (to my knowledge).

I hope we do see a variety of AIS transponder/VHF combos, but everyone needs to understand that they will have to pass many regulatory hurdles. In fact, the Standard Horizon GX6500 still awaits full approvals, though I understand that progress has been made.

Posted by: Ben at March 2, 2017 11:44 AM | Reply

Good to understand that a dedicated AIS antenna will perform better than a similar VHF antenna, because it's centered on 162 Mhz, not the 156 marine VHF norm.

Then again, I just realized that Vesper Marine has come up with an antenna that splits the difference and therefore should work well with their splitter:

Splitters and single antennas are a performance compromise, though, no way around it, though arguably a worthwhile compromise on single stick sailboats.

Posted by: Ben at March 2, 2017 12:31 PM | Reply

•Ben, you cannot mount a mast head AIS-specific antenna alongside a VHF antenna.

From the instructions: "Choose as high a mounting location as feasible, as free as possible from obstructions, and as far as possible from other antennas and strong sources of RF."

And Shakespeare tech support says they are having issues using this antenna with a splitter, so there's no comparative advantage using an AIS tailored masthead as a dual function VHF/AIS antenna over a common VHF antenna.

A shared VHF antenna at the mast head via a splitter is going to have way better "performance" than a separate AIS antenna on the stern pulpit mounted 50 feet lower. Not to mention the reduction in wiring, complexity, and installation issues. Hardly a compromise.

Hence the desire for an internal splitter with AIS class B.

All AIS transceivers are designed for external GPS antennas. You mean "AIS transceivers require a dedicated GPS antenna". Do you know the technical reason that is so, rather than just the current directive?

Posted by: Anonymous at March 2, 2017 2:13 PM | Reply

Ben, I have to say that a masthead antenna with quality coax centered on 156.8Mhz is going to outperform an AIS specific antenna at deck level. A sailboat specific combo radio / AIS B would have the GPS and splitter built in IMHO. Internal GPS may be a non-starter because of regs, but we can always ask :)

I have not seen the Vesper antenna, but if it is simply splitting the difference between VHF and AIS, I'm not sure I'm a fan. When I talk on VHF, I want the best performance possible. mayday and all..

Posted by: emsusa at March 2, 2017 3:26 PM | Reply

Thanks, Eric. I certainly won't argue with your appraisal, but couldn't some sailboats mount AIS antennas at spreader levels. Or couldn't you come up with some masthead superstructure that was decent for dual sticks. Titanium of course ;-)

Class B AIS with an internal GPS (receiver and) antenna is legit. Vesper XB series and Em-Trak B300 are examples. But they all have ports for external GPS because a diminished sky view will mean both poor position transmission and poor target accuracy.

The SH GX6500 obviously wasn't designed for medium or smaller sailboats. But maybe such a design will happen, as much as it can under the dual regulations. Sailboats are a small slice of marine electronics, but a much larger slice of AIS gear.

Odd thing, though. I think that a lot of Panbo commenters skeptical in general about electronics integration are the same sailors who want their AIS and VHF all mushed together and using one antenna.

Posted by: Ben in reply to emsusa at March 2, 2017 8:05 PM | Reply

The usual concern about an AIS transmitter (162-MHx) sharing an antenna tuned for a Marine Band radio (156.8-MHz) is the antenna VSWR will be high for the AIS transmitter, perhaps too high so a shutdown of the transmitter occurs.

If a "masthead antenna" is atop a 50-foot mast, we can assume the feedline is at least 60-feet long. Even if the feedline is very low-loss coaxial cable, say LMR-400, there will be more than 1.5-dB loss at the 162.-MHz. This cable loss will mask any VSWR problem for an antenna tuned for 156.8-MHz when transmitting on 162-MHz (AIS frequencies). Even if the actual antenna VSWR were 3:1, the effect of the 1.5-dB loss would present a lower VSWR at the transmitter, around 2:1, which should be tolerable for the AIS transmitter. Note that high VSWR increases line loss over the matched conditions, further masking the high VSWR to the transmitter.

The added height of the antenna tends to overcome any signal loss in the transmission line, so long as the line loss is held to a reasonable value.

Posted by: Jim Hebert at March 3, 2017 12:30 AM | Reply

Thanks, Jim, but I a little confused. When you say "mask" do you mean that the VSWR problem goes away or just doesn't show? Also while I think that a lot of boaters, and certainly techs, have gotten more aware of coax cable grades, I've yet to see a regular sailboat with LMR400 snaked up the mast.

Finally, I have heard that the digital nature of AIS signals is their saving grace, what helps relatively low power transmissions remain legible despite distance, mismatched antennas, lossy cables, splitters and so forth. Make sense to you?

Posted by: Ben in reply to Jim Hebert at March 3, 2017 4:42 AM | Reply

Anon, sorry I didn't see your comment yesterday afternoon (but note that simple registration means automatic comment approval and you can still stay anonymous).

At any rate, I certainly wasn't suggesting that anyone use an AIS antenna with a splitter. My point was that the two types of transmitters ideally have different antennas. Now this:

"A shared VHF antenna at the mast head via a splitter is going to have way better "performance" than a separate AIS antenna on the stern pulpit mounted 50 feet lower. Not to mention the reduction in wiring, complexity, and installation issues. Hardly a compromise."

First of all "way better" performance is not guaranteed. "emsusa" (Eric Steinberg) has a lot of experience with this and note his "quality coax" qualification. Moreover the second choice is not necessarily deck level. There are lots of AIS antennas mounted on spreaders, mizzen masts, and stern poles.

Also the NMEA recommendation for the horizontal separation of VHF antennas is 4 feet, along with the truism that "It is not possible to locate all antennas in
optimum locations. Most all installations are
a compromise."

And I just don't understand how two antennas is a "reduction in wiring, complexity, and installation issues" over a splitter. AIS/VHF splitters are active electronics, needing power and subject to failure.

Unless internal, which is fairly rare since the market is almost exclusively sailboats, splitters also require additional connectors and cable. Installing two sticks and running the cables is simply that, and you have two independent antennas. If one cable or antenna fails, you still have the other and could even conceivably switch a VHF to the AIS antenna manually to communicate.

Finally, while I'm not yet positive about how active splitters work, I'm pretty sure that they simply protect the AIS transceiver from VHF transmissions and that means no AIS output if you're transmitting on VHF. Most of us don't transmit very much at all, but then again Class B AIS basic info is only sent every 30 seconds at best, and your vessel name, etc. is only sent every 3 minutes. And there seems no question that a single AIS/VHF stick is not receiving any signals when VHF mic is open.

In Class A world, transmitting at 12 watts instead of Class B's 2 watts, I don't believe that antenna splitters are allowed.

Posted by: Ben in reply to Anonymous at March 3, 2017 5:42 AM | Reply


You may not be surprised that Merrimac has Ecoflex 10, which has 4.8 db/100m loss at 144 Mhz, very similar to LMR400, up its mast all the way.

If you intend participating in a World Sailing Offshore Special Regulations class 2 event you must have:

an AIS Transponder which either:
- shares the masthead VHF antenna via a low loss AIS antenna splitter; or
- has a dedicated AIS antenna not less than 38 cm (15”) in length mounted with its base not less than 3 m (10’) above the Waterline and co-axial feeder cable with not more than 40% power loss (Loss Estimator)[19870].pdf
rule 3.29.13.

I started out with the latter, a separate antenna at about 4,5 m above the waterline, but I switched to a splitter later on. My AIS receiving distance of not-so-high ships and the transmitting distance doubled, at least. I do notice that AIS distance at which you start seeing yachts varies dramatically. With big ships it may as well but it happens at such large distances that I don't care. In other words, I am a firm believer in the-higher-the-better.

A friend of mine tested ~ 10 splitters, and found their efficiency in passing through the high power of the VHF to vary quite dramatically. Given a 25 W sender some consumed over 8 W of that. Others consumed less than 2 W, meaning they passed along 23 W.

Posted by: Kees at March 3, 2017 6:17 AM | Reply

Thanks, Kees, but I did say "normal sailboats" ;-)

I've heard that at least a couple of people really objected to the OSR endorsement of splitters, but I don't doubt the value when done well. But then again, aren't racers a lot more sensitive about weight and windage aloft? Also, did you consider two masthead antennas a couple feet apart?

If your friend's splitter testing is published somewhere, can you link, or just maybe tell us which splitter you are using?

I'm not familiar with EcoFlex 10 (or 15) but see lots of dope here:

Posted by: Ben at March 3, 2017 7:19 AM | Reply

> But then again, aren't racers a lot more sensitive about weight and windage aloft?

IMO recreational sailors should care about weight just as well. Every kilo at the mast top negates many more kilos in the keel, making the boat more tender. If you have a mast n meters high, and a keel with weight centered k meters below the center of gravity C, a 1 kilo VHF antenna + holder at n meters from C, coupled with a cable weighing 100 g/m, thus adding 0,1 * n kilos at n/2 meters from C, at least. For my mast and VHF antenna that adds up to (1 * 30 + 0.1 * 30 * 30 / 2) / 1.5 = 50 kilos of keel negated.

> Also, did you consider two masthead antennas a couple feet apart?

No, not really as it was an after-the-fact change to move to the shared VHF antenna. With the wind unit, 3 colour light, anchor light, windex, VHF and lightning protector it's already pretty busy up there.

My friend can't publish his information unfortunately due to conflict of interest.

I'm using the Navico NSPL-400.

Posted by: Kees in reply to Ben at March 3, 2017 9:47 AM | Reply

IMHO Very simple. Just attach the AIS antenna to the stern rail. The range is good for the primary purpose of the technology, collision avoidance, and you don't risk compromising your VHF with a spliter, etc. as would happen if you share an antenna.

The height of the stern rail is just fine. Your range will be proportional to how big the other vessel is. For example a tug transmitting from a 50 foot mast will be plenty visible on AIS before you care, and although short maneuverable recreational boats won't be seen until they are closer, they will still be detected long before you would consider avoiding them.

Posted by: Dan Corcoran (b393capt) at March 3, 2017 1:57 PM | Reply

Up until a few weeks ago, my 5250-AIS "Mini" AIS antenna was on the radar mount, about 35' ASL. Unfortunately, apparently while we were enjoying Fort Myers, it failed, as revealed by my MFJ 226 analyzer, so I shifted to a stern-mounted antenna (an Shakespeare HS-2774-1). The difference in performance was noticeable.

As to collision avoidance, the stern mount is OK - I can see big ships at 10 miles +. so no issues there -- but as for finding friends, it's not nearly as nice, as my range to other low-mounted Class B units is only a few miles. No more sniffing out who's in the anchorage 10 miles ahead..:)

When we're not cruising, I'll be heading up to get the high AIS antenna back online ASAP.

I'll see your LMR400 with 1/4" Superflex :) It's even the sky-blue color! [But it is really pesky to pull around corners]

Just waitin' out the wind in Marsh Harbor :)

Posted by: Hartley at March 4, 2017 3:26 PM | Reply

found it and unfortunatly it confirms seperate AIS and marineVHF antenna connectors. Also it seems like a cradle for the RAM4wirless is needed, which i havent found a price for yet. Looks good otherwise though.

Posted by: Johan in reply to Johan at March 5, 2017 7:19 AM | Reply

I found the US Federal rules that would appear to preclude a VHF Comm/AIS with a single antenna port. This was not a trivial search, especially since I wasn't about to spend money on IEC or NMEA standards docs :)

In the US, all AIS units have to pass muster by the USCG before the FCC will approve them, and under 33CFR164.46 (33CFR is where the USCG Regulations are found) any AIS that is installed in a required vessel (which includes Class A and Class B units) to be "properly installed" must meet several IMO guidelines, which includes 'Safety of Navigation Circular 227', which under 2.2.1 "VHF Antenna Installation" includes the following:

** "Ideally there should not be more than one antenna on the same level. The AIS VHF antenna should be mounted directly above or below the ships primary VHF radiotelephone antenna, with no horizontal separation and with a minimum of 2 m vertical separation. If it is located on the same level as other antennas, the distance apart should be at least 10 m."

This clearly precludes the possibility of either using a splitter or a common antenna for an AIS unit that would be installed in a "Required" vessel. Those of us who are "voluntary equipped"(most recreational yachtsmen) wouldn't need to meet this, but a manufacturer of a certified Class B unit probably has to.
Ben, I don't think Gizmo has 10m of space available on top to separate VHF antennas, and I know Atsa doesn't. I found one AIS manufacturer (Nauticast) that recommended a minimum horizontal spacing of 2 meters for their Class B - still not easy for a masthead. My experience in land mobile radio suggests to me that anything closer is definitely going to have interaction.

If you're interested in the USCG page that contains this stuff, here it is:

Posted by: Hartley at March 5, 2017 4:49 PM | Reply

Hartley, a splitter sharing one antenna would seem to meet the "no more than one antenna on the same level requirement". Its one antenna. Shared. And anecdotally as we see in the above posts, its works better than two seperated vertically by the 50 feet or so as required in a masthead and stern pulpit installation as necessary for sail boats.

I hope Standard Horizon comes out with a splitter version. And I'm still curious about the technical reason Class B AIS transponders require dedicated GPS antennas. After all DSC radios broadcasting GPS seem to do the same function as an AIS transmitter...and they use shared GPS antennas.

I would pay top dollar for a VHF/AIS transceiver/splitter with an integrated GPS antenna or shared GPS off the N2K backbone. It would make for an elegant installation and minimal complexity.

Posted by: Anonymous at March 5, 2017 10:09 PM | Reply

> And I'm still curious about the technical reason Class B AIS transponders require dedicated GPS antennas.

The AIS method of operation requires all transmitters to know exactly when they are going to transmit, in order to avoid clashes. In every transmission a sender 'allocates' a particular timeslot, up to 5 minutes ahead. The system depends on everyone using the same idea of when a particular timeslot is, so each transmitter must have a millisecond precise idea of how late it is. A serial or network attached GPS makes this much harder to achieve, if not impossible. So to avoid any issues, all AIS transmitters must have their own dedicated GPS that is attached directly. The (analog) antenna may be connected via a wire, but the GPS decoder logic must be internal.

Posted by: Kees in reply to Anonymous at March 6, 2017 9:37 AM | Reply

Kees, thanks for the clarification, but that makes a VHF/AIS transceiver/Splitter with an integrated GPS receiver (internal antenna and GPS decoder) quite feasible. Check out Raymarine and other VHF radios with integrated GPS. And if my iPad GPS has no trouble below decks finding satellites neither should the VHF/AIS.

I hope Standard Horizon et al are listening.

Posted by: Anonymous at March 6, 2017 9:51 AM | Reply

Thanks, Kees, also for IDing your splitter, which I was just checking out.

It's interesting that the Navico NSPL-400 splitter... "No insertion loss on AIS and VHF Rx" and "Low insertion loss on AIS and VHF Tx."

Meanwhile, the Vesper Marine splitter...

... claims insertion losses of "VHF RX

And the SRT Em-Trak splitter (which the Navico and others may be related to)... "zero performance loss" (in the brochure) but isn't specific about where.

The Em-Trak manual does confirm what we've been saying about splitters not permitting AIS transmissions when the VHF transmit button is keyed:

"In the event that both the VHF radio and AIS transceiver are transmitting at the same time, the AIS antenna splitter will give priority to the VHF radio."

That's why I've sometimes suggested that on power boats an AIS/VHF splitter is best used with the backup VHF radio.

Also why separate AIS and VHF transmit antennas are better even if quite close together horizontally; at least the AIS transmissions have some chance of getting out.

Posted by: Ben in reply to Kees at March 6, 2017 10:10 AM | Reply

> Also why separate AIS and VHF transmit antennas are better even if quite close together horizontally; at least the AIS transmissions have some chance of getting out.

You also have a chance of blowing the AIS receiver hardware whilst transmitting on VHF, due to a (too) large fraction of 25 W being put into that poor receiver.

Posted by: Kees in reply to Ben at March 6, 2017 10:12 AM | Reply

Walk talk about that as a possibility, but in modern day radios it hasn't proven to be an issues at these lower powers (less than say 100 watts) My portable VHF is not getting damaged by my main VHF.

I have no scientific evidence, other than having done similar on fleet of about 300 vehicles.

Posted by: Howard in reply to Kees at March 6, 2017 10:29 AM | Reply

Hartley, thanks for what looks like good research and analysis. I suspect that the Class B regs may assume a dedicated antenna, or least ignore the splitter possibility.

I once saw the insides of a combined True Heading Class B/splitter and the electronics were separate SRT modules. I suspect that only the Class B module had to be tested because (like AIS receivers) there are no standards for splitters:

Incidentally, the Em-Trak splitter FAQ confirms that "Class A transceivers are required (by regulation) to be connected to their own VHF antenna."

Posted by: Ben in reply to Hartley at March 6, 2017 10:33 AM | Reply

Anon, the requirement for separate antennas is clearly aimed at allowing both devices to operate simultaneously without interference - which, as Ben pointed out, is not possible with a splitter and is compromised even with separate antennas if they are too close together.

I didn't paste the entirety of section 2 of the IMO Guideline, but other parts make the non-interference intent quite clear. I would urge you to go read the entire Guideline to get a feel for the intent there.

With "voluntary equipped" vessels like mine and probably yours, the USCG is not concerned if a few of our transmissions are lost or mis-timed, but I suspect they are VERY concerned that "Required equipped" vessels have EVERY transmission going out, and properly timed to avoid interference, even if the vessel has a Class B AIS transponder.

If you look in the rules for Class A AIS transponders, you see that their primary GNSS input is from the vessel's "primary navigation system", with a backup of an internal GNSS receiver.
[GNSS = Global Navigation Satellite System, AKA GPS, though others would suffice (GLONASS, etc.)]
For Class B, they utilize only the internal unit, and as Kees & Ben pointed out, it is used for signal timing and VERY required.

And Kees is right - antennas very close together will couple a LOT of energy - damage to the receiver is certainly a possibility.

Posted by: Hartley in reply to Anonymous at March 6, 2017 10:34 AM | Reply

Kees, thanks for the clarification, but that makes a VHF/AIS transceiver/Splitter with an integrated GPS receiver (internal antenna and GPS decoder) quite feasible. Check out Raymarine and other VHF radios with integrated GPS. And if my iPad GPS has no trouble below decks finding satellites neither should the VHF/AIS.

I hope Standard Horizon et al are listening.

Posted by: Anonymous at March 7, 2017 12:32 PM | Reply

Anon, you really ought to peek at the regulations and testing mandated for VHF marine radios and AIS transponders. Much of it is pretty easy to find.

And consider this: VHF and AIS are both competitive categories. If what you think is quite feasible and quite desirable, why hasn't some company made it?

PS I'm fairly sure that Standard Horizon made the first VHF radios with built-in GPS, both the handheld and the fixed versions.

Posted by: Ben in reply to Anonymous at March 7, 2017 2:10 PM | Reply

To follow-up on the question about how transmission line loss will mask a high VSWR at the antenna:

Consider a 100-Watt transmitter feeds into a transmission line with 3-dB loss. This means that only 50-Watts reaches the antenna.

If the antenna has a mismatch of VSWR 3:1, then of the 50-Watts applied, 12.5-watts is reflected.

The reflected 12.5-Watts travels back through the transmission line, again attenuated by 3-dB, so at the transmitter the reflected power is now about 6.25-Watts.

If a directional wattmeter is inserted at the transmitter, it sees:

Forward power = 100
Reflected power = 6.25

The transmitter sees a VSWR of 1.67:1

The transmitter is quite happy transmitting into a 1.67:1 VSWR. The actual antenna VSWR is 3:1. but the transmitter has no idea, as it thinks it is sending into a load with a 1.67:1 VSWR

A further problem (not to be handled here) is that line loss increases with VSWR, so the 3:1 VSWR at the antenna will cause the transmission line loss to increase.

Posted by: Jim Hebert at March 7, 2017 3:03 PM | Reply

To reply to the question of how digital transmission affects receiver sensitivity and thus range of communication:

The digital data receiver is a typical AIS receiver is rated for sensitivity in the same manner as a voice receiver: a certain signal level at the antenna input will produce a certain output signal with particular characteristics.

For voice, the output signal is usually qualified by its ratio of signal to noise-and-distortion or SINAD. A typical voice FM communication receiver can produce an output signal with 12-db SINAD from an input of -119dBm.

For data, the output signal is usually qualified by its packet error rate (PER) percentage. A typical AIS receiver can produce an output signal with a PER of 20-percent with an input signal of -107dBm.

The receiver sensitivity is better on the voice receiver by 12dB.

The voice signal is normally sent at 25-Watts. A Class-B AIS signal is sent at 2-Watts. There is a 10-dB advantage to the voice transmitter.

This gives voice a 22dB advantage over digital on VHF Marine band. The advantage to digital is the demodulator is electronic the modulation is precise, consistent, and always 100-percent, and the output is real data.

With voice, the demodulator output is acoustic power and recover of data is by the operator's ear. The skill of the operator can vary greatly, and so can his attention. The digital demodulator is relentlessly listening and always performing at the same level. Can a particular operator produce copy with less than a 20-percent error rate at 12-dB SINAD? It depends on his skill, and also perhaps on the clarity of the person transmitting, their microphone technique, the modulation level, and so on.

One advantage to data is the short duration. An AIS transmission is just a tiny burst, a few milliseconds. A voice transmission of the same data might take a minute. If the path has fading, the data burst might be received intact, but a long voice transmission might fade out and data would be lost.

An AIS transponder at its shortest interval is retransmitting every five seconds. So in a one minute period it gets 12 chances to be received. The longer voice transmission may not be clearly copied during the entire minute.

Posted by: Jim Hebert at March 7, 2017 3:28 PM | Reply

Thank you Jim. Reading your post was like receiving an extra Panbo entry this week.

That was so informative and changes how I think about digital communication vs voice in the VHF frequency range, foremost wiping out my belief that digital signals have it easy getting between stations.

Posted by: Dan Corcoran (b393capt) at March 9, 2017 1:43 PM | Reply

Dan--thanks for those kind words.

To elaborate a bit further:

In VHF Marine Band radio the modulation technique for voice is FM (or PM). Using FM for voice is particularly bad for weak signal work. FM demodulators have non-linear behavior as signal strength changes. This is commonly called the "knee effect." If a frequency-modulated voice signal is strong enough to be above the detector's threshold, then there is very good recovery of the voice modulation. But if the signal level begins to fall below the detector threshold, the recovered modulation is very significantly degraded. For this reason, FM-modulated voice can be very difficult to copy at marginal signal levels.

The advantage to FM modulation accrues when the signal is above the detector threshold. The recovered voice modulation will tend to have a very good signal-to-noise ratio, making it easily copied. And there is the inherent immunity to analog noise sources of the method. Generally the FM signal is either in two states: strong enough to deliver good copy, or not there at all. An example of marginal copy of a weak FM voice signal can be heard here:

The above link is to a recording of a NOAA weather station coming in at a range of 105 miles. Did you get 100-percent copy on this on the first listen?

Posted by: Jim Hebert at March 10, 2017 9:31 AM | Reply

Yes, thanks a lot for the further explanations, Jim.

Also one thing I've been busy with recently is testing a Digital Yacht AISnet V2 receiver for use as a volunteer tracking station and also to test some new Em-Trak AIS transponders on Gizmo. It turns out that my rooftop antenna is pretty poor and when I hunted for better, I found this excellent and informative Jim Hebert review:

Is the InnovAntennas yagi still working well, Jim, and are you perhaps aware of less expensive alternatives?

Posted by: Ben in reply to Jim Hebert at March 11, 2017 9:00 AM | Reply

Re the three-element "bespoke" design Yagi from InnovAntenna: this antenna is a great AIS or general VHF Marine Band antenna. Its construction is excellent. I think you could put up this antenna and it would survive the weather for 20-years or more. And the antenna's performance is excellent; it has gain and a good pattern, and it is very quiet on receive due to the loop driven element. But note that this will be a directional antenna, so you need a situation where you expect the AIS signals to all come from one quadrant of the compass. The beamwidth will be a bit less than 90-degrees in the horizontal plane.

Since the time when I had them custom-make this antenna, the manufacturer can now ship direct to customers in the USA from the UK.

There are only two aspects I would mention that might be slight drawbacks for a boater who is not accustomed to radio techniques:

--the antenna needs a coaxial choke balun; you have to make this yourself. It is not difficult to make the balun as it is just a few turns of the transmission line made into a coil; I illustrate the choke balun in my article

--the antenna will need a bit of tuning of the driven element; since most boaters have no way to transmit on the upper end of the marine band, you have to tweak the VSWR for the AIS channels as best as you can with measurements from the low-end of the band.

Also, after several years exposure to weather, I found the bottom end of the loop driven element collects some water, so I would recommend taping over the slotted joints on the loop element, or possible making a small hole in the bottom of the loop to let any water drip out.

Posted by: Jim Hebert at March 11, 2017 10:23 AM | Reply

Thanks, Jim. You can see details of my Marine Traffic station here:

90 degree coverage would work OK for me but I was hoping for more like 135. Interestingly, even a very old VHF antenna and high loss coax I sometimes getting the Lincolnville-Isleboro ferry when its on the island side of its route that's behind the small mountain that quite blocks my location to the northeast (clearly seen if you zoom in on the satellite map).

At any rate, I will next try a better quality VHF boat antenna with mostly LMR400 cable, but I remain curious about alternate antennas for this use.

Posted by: Ben in reply to Jim Hebert at March 11, 2017 2:02 PM | Reply

Ben--I think the pattern of a three-element Yagi would be perfect for your location.

By the way, I see that Innovantennas now offers stock models for AIS antennas. (When I bought mine it was a bespoke or custom design.) I also see they include some sealer compound, and refer to the antenna as having an N-connector; that suggests they are including a choke-balun and short feedline jumper. This adds to the total value compared to the bare antenna I bought at about $100. The price (£128 or about $157) is still reasonable, in my opinion, as the construction quality of the antenna is excellent.

The azimuth plot of the three-element is shown at

The plot shows that at 45-degree off axis the antenna gain is down 7-dB, so at that heading the antenna still has 1.7dBi gain.

Antenna height is really the most important factor. If you can install an omni-directional vertical at high elevation, it will work well, too.

As for an alternative Yagi antenna, your New England neighbor Cushcraft Antennas offers a $70 three-element 144-MHz yagi that could be re-tuned to work on 162-MHz.

The re-tuning might be accomplished with some advice from the factory, but I suspect it would be a bit tedious for the average boater to undertake.

Another option is the $50 HyGain antenna shown at

An approximate retuning of those antennas could be done by just scaling all the element lengths by the inverse ratio of frequencies, i.e., by a factor of 144/162 or 0.88. The element positions on the boom could be scaled in a similar manner, working from the driven element position. That could save some money.

For receive-only at VHF, transmission line loss is not as critical. But lower transmission line loss always helps when received signal levels fall to the threshold of being useful.

Posted by: Jim Hebert at March 12, 2017 12:42 PM | Reply

Thanks, Jim. I suspect that you and your review encouraged Inno to make the AIS antennas part of their regular line. Also may have encouraged the MT volunteer listener just north of me, which is where I first saw it mentioned. I don't know him or how his 3 el is set up, but he's getting 100 mile max ranges quite frequently during the busy season:

Posted by: Ben in reply to Jim Hebert at March 12, 2017 2:15 PM | Reply

ASIDE to Ben: that AIS receive station link is very interesting. Note how the "max distance plot" of direction of stations received corresponds quite well with the antenna pattern. Also, note that in summer he receives a lot of greater-than 100-mile-distant signals; there is probably some air temperature (inversions) or other atmospheric effects enhancing propagation (and probably greater ship density, too). His best DX is 413-miles--impressive.

Posted by: Jim Hebert at March 12, 2017 4:29 PM | Reply

Re the notion that regulations compel use of a dedicated antenna for a Class A or Class B AIS device:

--I saw the comment from em-trak that says Class-A AIS transponders MUST use a dedicated antenna; but I don't find that authoritative. If there are regulations regarding a provision like this, it ought to be possible to find them and cite them. A manufacturer's FAQ is not exactly a primary source;

--the comments that if one reads certain regulations in their entirety then they could "feel their intent" and make a deduction that a dedicated antenna MUST be used are hard for me to understand. In regulations, I would expect words like SHALL or MUST or even SHOULD would be used to clearly state the requirement that a dedicated antenna be used.

I inquired with Standard-Horizon about their motivation for using a separate antenna connection for the AIS transponder in the GX-6500. They want to provide maximum radio performance, and to not have their radio's performance degraded by a splitter. On that basis, I don't see that there were any regulatory influences that caused them to create this design as they did.

Posted by: Jim Hebert at March 15, 2017 11:11 AM | Reply

Hello Jim,
Have you looked at the various documents I referred to? Consulting 33CFR164.46, we find that to be considered "Properly Installed", an AIS installation must meet several requirements: IMO Resolution A.917(22) and SN/Circ 227, 244, 245 and 289. Circulars 227 & 245 may be substituted with NMEA 0400-3.10.

A.917(22) says, in part:

5 Shipborne AIS (see Figure 1):
-continuously transmits ship's own data to other vessels and VTS stations;
-continuously receives data of other vessels and VTS stations; and
displays this data.

Since the installation of a splitter would preclude compliance with this section alone, I would suggest that such an installation would preclude compliance with 33CFR164.46.

Recreational vessels (voluntary equipped vessels) need not comply with this regulation - but any vessel that is required to carry AIS (which could be Class A or B) would have to.

The FCC (in 47CFR80.231) requires that all Class B AIS devices be certified compliant with IEC 62287-1 before they can be sold in the US. This document costs several hundred dollars, so I have elected not to obtain one - perhaps you would be interested?

73 DE Hartley

Posted by: Hartley in reply to Jim Hebert at March 15, 2017 11:46 AM | Reply

I'm not sure that anyone suggested that Class B AIS is required to use a dedicated antenna, just that it's preferred. I also suspect that the regs Hartley found apply to certain vessels but not all that carry Class A. In fact, the Vesper splitter (and maybe others) can handle 12.5 watts:

By the way, Em-Trak (SRT) is pretty authoritative about AIS, which is their only business:

And the Garmin AIS600 is an example of an approved Class B with an antenna splitter built in:

Posted by: Ben at March 15, 2017 12:14 PM | Reply

Re regulations cited by HARTLEY which say:

"5 Shipborne AIS (see Figure 1):
-continuously transmits ship's own data to other vessels and VTS stations;
-continuously receives data of other vessels and VTS stations...

The AIS transponder does not continuously transmit; it only transmits at intervals, depending on the vessel speed and situation. I don't see that the transmitting comment compels a dedicated antenna.

The requirement to continuously receive COULD be construed to mean a "Shipborne AIS" has to be able to receive while it is transmitting, and thus must have separate receive and transmit antennas and the ability to listen with proper receiver sensitivity while it is transmitting. I don't see those interpretations as being outside the realm of possible interpretations of the cited section.

The inference one can draw from those sentences is not limited to the one you have drawn, i.e., a dedicated antenna is needed. You could just as easily decide that full-duplex operation was needed, and, since the receive and transmit on are the save frequencies, that would be quite impossible to implement in the confines of space of a small ship, even one large enough to need Class-A devices.

This sort of interpretation is problematic. If there is language that compels use of a dedicated radio antenna, it ought to be much clearer than the cited language.

Posted by: Jim Hebert at March 15, 2017 4:43 PM | Reply

You are all missing the point, that you are compelled to have Mizzen or foremasts.

Sloops are passe

Posted by: sheldon haynie at March 15, 2017 5:05 PM | Reply

The SOTDMA access scheme used by Class A AIS devices needs to receive all the time (except during its own transmissions). This access scheme is complex and requires significant information about the VDL and the other devices using it. Thus, it needs its own antenna.

The CSTDMA access scheme used by current Class B devices is much simpler and does not need to receive all the time. Hence, sharing an antenna with a VHF radio is not such a problem. However, if the VHF radio is in frequent use, even a rail mount dedicated antenna for the AIS would be preferable to sharing the one up the mast.

Posted by: Anonymous at March 15, 2017 7:51 PM | Reply

em-trak is the house brand for SRT, and I do agree that SRT is an extremely important player in AIS device technology and manufacturing. But citing their FAQ is not authoritative in regard to actual regulations. If regulations exist that compel certain features, then we should be able to have a cite to the regulations that clearly compel those features.

The technical and operational requirements for AIS are laid out in

"Recommendation ITU-R M.1371-4, Technical characteristics for an automatic identification system using time-division multiple access in the VHF maritime mobile band"

Regarding incorporation of a GNSS receiver in an AIS Class-B device, ITU-R M.1371-4 has this to say:

"3.3 Internal GNSS receiver for position reporting

"The Class B “CS” AIS should have an internal GNSS receiver as source for position, COG, SOG."

On the subject of antennas for AIS devices, however, the recommendation is quite silent. It only says:

"2.14 Safety precautions

"The AIS installation, when operating, should not be damaged by the effects of open circuited or short circuited antenna terminals."

That is the only mention of the word "antenna" in the document.

Posted by: Jim Hebert at March 17, 2017 9:56 AM | Reply

You are quite correct, Jim, there is not a requirement in the standards for a dedicated antenna for an AIS device. However, it is a derived requirement for Class A devices based on their method of operation. Sharing an Antenna with a VHF radio means the operation of the AIS device is significantly impaired, quite possibly to the extent of non-compliant behaviour, when the radio transmits. Thus, to guarantee a Class A AIS device operates in compliance with its standards it must use a dedicated antenna.

So there is no clause in a standard to reference, it is implicit in the way Class A AIS devices work.

Posted by: Anonymous in reply to Jim Hebert at March 17, 2017 7:02 PM | Reply

Who knew that many marine VHF channel numbers are changing? Yup, all the Alpha channels like 21A, 22A and 23A are becoming 1,000 bigger, as in 1021, 2022, and 1023. Actual frequencies are not changing, just the channel names. Chuck Hawley has the story here:

The USCG has the new channel list here:

That list is also a good place to see how AIS transmissions live at the very edge of the marine VHF band (and also why an AIS antenna should also be quite good at receiving WX stations).

Posted by: Ben at March 18, 2017 9:35 AM | Reply

I believe the changes in channel numbering were announced back in October 2016 on the USCG page (linked above). That's when I notice them.

In this process four NEW simplex channels have been created by taking over the lower frequency of the formerly duplex channels 19, 20, 79, and 80.

Some of the new channels are to be used for "VDSMS" or VHF-FM Digital Small Message Services.

And two of the new channels are allocated for future "application specific message" use, designated ASM-1 and ASM-2.

More details at

with many links to the actual regulations, FCC requests for comments, and RTCM announcements.

Posted by: Jim Hebert at March 18, 2017 10:07 AM | Reply

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