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  #21  
Old 10-23-2013
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Re: VHF AIS radios

Thanks T5.. Saves me asking you!

Quote:
Originally Posted by SVAuspicious View Post
Splitters are fundamentally bad. The best thing you can do is have independent VHF antennas for VHF and AIS.
Yep, understand that. It just not practical on small(er) boats..

I figure, for the sailing I do (mostly on what is effectively a large lake, open to the sea at one end) and a mast-head antenna, the receive range reduction should (cross fingers!) not be so great as to cause any major issues.
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Old 10-23-2013
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Re: VHF AIS radios

Quote:
Originally Posted by JonEisberg View Post
I'm very happy with the Standard Horizon GX 2150, a terrific radio even without the AIS... I'd choose it over an Icom anyday, largely due to the fact that the Icom connectors for a cockpit remote mic are absolute pieces of crap, guaranteed to fail over time...

I have no interest whatsoever in "networking" my systems, so the 'old-fashioned' NMEA 0183 doesn't bother me at all...
John,

Fifteen years ago I was a huge ICOM fan, they were simply better VHF's way back when. Today, not so much performance separation. At the Annapolis show I actually saw people walking around with ICOM RAM mics preparing to shove them up the butts of anyone working the ICOM booth.......

Since moving away from ICOM, due to poor product reliability, mostly remote mic cords, I have not looked back from Standard Horizon. The radio is a work horse, reliable and Standard Horizon is one hell of a company to deal with if you have to. They have great support and great turn around.

We have the Matrix AIS 2100 and it has performed flawlessly. Even drives our fog horn, has a hailer and many other great features. The mic cord on our RAM mic has been bullet proof and in the fog here in Maine it gets LOTS of use. We also monitor VHF 16 with it at all times so it has lots of hours. My only gripe is they really ought to have a N2K compatible model by now. Also the RAM mic cord is very stiff but I've not yet seen one broken, unlike the ICOM RAM's...

Just got done dealing with a Ray VHF issue. VHF was very noisy and influenced by nearly anything AC or DC you turned on. Ferrites, chokes the whole gammut, nothing worked. Ray was of no help and wanted to do a flat rate repair that cost more than a new radio... Replaced it with a Matrix AIS 2150, dead silent, no noise, no interference and using the same circuit and VHF antenna.....
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Last edited by Maine Sail; 10-23-2013 at 07:48 PM.
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  #23  
Old 10-23-2013
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Re: VHF AIS radios

If they are so good, it's a shame Standard Horizon don't market over here. We get a choice of Icom, Raymarine, Simrad and GME..
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Old 10-23-2013
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Re: VHF AIS radios

Quote:
Originally Posted by SVAuspicious View Post
Splitters are fundamentally bad. The best thing you can do is have independent VHF antennas for VHF and AIS.
Not sure if you noticed that the built-in splitter is circuit-protected, which I presume to mean that it blocks the VHF radio's 25W transmissions so it won't fry the electronics. I know this does not address all the issues with splitters, but it would seem to be a significant improvement vs. someone who unknowingly puts a passive splitter in place without realizing the damage that it can do when he presses the button on his mic.

As someone else pointed out, compromises sometimes have to be made on small boats. One of the reasons I decided to go with the GX2150 is because it did not require a splitter and all the potential problems that go along with it. But for others who don't want to replace their VHF, this add-on looks to be a nice design, and allows you to use the masthead antenna instead of placing a second antenna in a less favorable position.

EDIT: I'm sounding too much like a know-it-all here. I'd be happy to hear more specifics on the problems caused by using splitters. I have a lot to learn about these things, especially if you have personal experience with them.
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Last edited by TakeFive; 10-23-2013 at 10:24 PM.
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  #25  
Old 10-24-2013
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Re: VHF AIS radios

Quote:
Originally Posted by Classic30 View Post
Quote:
Originally Posted by SVAuspicious View Post
Splitters are fundamentally bad. The best thing you can do is have independent VHF antennas for VHF and AIS.
Yep, understand that. It just not practical on small(er) boats..
I recommend a masthead antenna for your VHF and an AIS/VHF antenna on your pushpit. As an alternative, especially if you haul for the winter with mast down, put the AIS antenna on a spreader. How is that not practical on a small boat?

Quote:
Originally Posted by TakeFive View Post
Not sure if you noticed that the built-in splitter is circuit-protected, which I presume to mean that it blocks the VHF radio's 25W transmissions so it won't fry the electronics. I know this does not address all the issues with splitters, but it would seem to be a significant improvement vs. someone who unknowingly puts a passive splitter in place without realizing the damage that it can do when he presses the button on his mic.
Any splitter that will be at all functional if either leg includes a transmitter must have some active component.

Splitters function by dividing the energy gathered by the antenna between two downleads to the receivers, in this case the fixed VHF and an AIS. The only difference in the GX-2150 and similar is that all the connections are internal to the radio. You still take a 3 dB attenuation of the signal, which means half the power absent the splitter. Remember, decibels (dB) measure the ratio of power - db = 10 log (P1/P2) so small numbers make a big difference. PL-259 and SO-239 connectors are not so great either so an external splitter will be even worse with additional attenuation of 0.5 - 1.0 dB (depending on the skill of the connector installer) from the extra two connectors. The impedance bump (you can't count on a continuous 50 ohm characteristic impedance through the connectors and splitter) results in increased SWR which on most radios will roll back power output on transmit.

Now on the subject of transmit, most splitters I am familiar with have a 1.5 - 1.8 dB attenuation on transmit.

In commercial (like cable TV) and government (like SIGINT) applications where splitters are used to share very expensive, high performance antennas there is a low noise amplifier (LNA) ahead of the "splitter" and a carefully implemented, constant impedance divider network, often followed by another LNA. Noise levels are critical - you can't just amplify the signal, you have to amplify the signal without increasing the noise floor. You do not want to think about what those cost. *grin*

Transmitters get dedicated antennas. In applications that spend serious money on signal distribution, don't you think that if there was a fundamentally good way to use a splitter with a transmitter they would?

Regardless the physics and the engineering are clear. Splitters, internal or external, at the price point available to the recreational market introduce significant signal loss AND increase the noise floor.

Now for the "compromises are necessary" contingent the question becomes whether it is significant. How big a difference does it make?

Fixed radio to fixed radio you probably won't be able to tell most of the time. Talking to the USCG over Rescue 21? Probably not discernible. However, calling a marina when the dockmaster has a handheld and is out walking the docks? It will make a difference that may mean the difference between contact and not. Entering an inlet where your local knowledge is over a hill and the other side of a forest of masts? Could be a problem. Trying to maintain contact with the Towboat/US tow boat on it's way to haul you off a soft grounding? There may be delays as you relay through the tow base.

I've been working with radio systems for a long time both professionally and as an avocation. Splitters are not a good compromise. I have yet to see a boat that can't manage a proper installation of separate antennas for fixed VHF and AIS.

Quote:
Originally Posted by TakeFive View Post
One of the reasons I decided to go with the GX2150 is because it did not require a splitter and all the potential problems that go along with it.
Don't kid yourself. The GX-2150 does have a splitter. It's built in to the radio. All the same deficits apply.
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Last edited by SVAuspicious; 10-24-2013 at 07:45 AM.
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  #26  
Old 10-24-2013
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Re: VHF AIS radios

Quote:
Originally Posted by SVAuspicious View Post
...Fixed radio to fixed radio you probably won't be able to tell most of the time. Talking to the USCG over Rescue 21? Probably not discernible. However, calling a marina when the dockmaster has a handheld and is out walking the docks? It will make a difference that may mean the difference between contact and not...

...Don't kid yourself. The GX-2150 does have a splitter. It's built in to the radio. All the same deficits apply.
I am familiar with most of what you describe, though I do not have nearly as much experience. It's obvious that splitting the antenna output two ways would reduce the strength by 3 dB. As you point out, S/N is just as important, and is why I have my home TV antenna amplifier right at the antenna (so I'm amplifying the purest signal, and not amplifying the noise that my wires pick up).

As a technical matter, the GX2150 does have a splitter somewhere in there, since there are at least 3 radios - the standard VHF radio, and the two separate receivers dedicated to AIS channels 87 and 88. But unlike when you mix and match two devices from two different manufacturers, the GX2150 is designed, tested, warranteed, and reviewed as a single unit, so the complications that you describe are addressed by the manufacturer. So while I don't dispute the theoretical issues that you mention for splitters, as a practical matter I've never heard any complaints about the GX2150 having "all the same deficits." In fact, the reviews that I have seen have been overwhelmingly positive. Can you point me to some test results that show that the GX2150 has difficulties hailing dockmasters at marinas?

As for your suggestion about installing an AIS antenna on the spreader of a small boat, since small boats have short spreaders, the antenna would have to be pretty close to the mast. Wouldn't the presence of the mast so close to the antenna create a blind spot due to shadowing of the signal? Personally, I'd rather have the antenna at the masthead where it gets an unobstructed 360 degree view, and maximum distance to the horizon.
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  #27  
Old 10-24-2013
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Re: VHF AIS radios

Quote:
Originally Posted by TakeFive View Post
It's obvious that splitting the antenna output two ways would reduce the strength by 3 dB. As you point out, S/N is just as important, and is why I have my home TV antenna amplifier right at the antenna (so I'm amplifying the purest signal, and not amplifying the noise that my wires pick up).
Exactly. That's the same reason satellite dishes put LNAs at the feed, that GPS "antennas" are really the antenna and receiver integrated together, and even that depth sounders (acoustic vice electromagnetic) now have demodulation built into the sounder. Noise and attenuation are less critical at lower frequencies like VHF and HF, but are none the less still important. At VHF we worry more about impedance (my earlier note on connectors) and attenuation (why RG-213, RG-8X, or LMR-400 are better choices for VHF than RG-58). At HF we worry about inadvertent shielding, multipath, and interference so tuner location and grounding become the first order factors.

Quote:
Originally Posted by TakeFive View Post
As a technical matter, the GX2150 does have a splitter somewhere in there, since there are at least 3 radios - the standard VHF radio, and the two separate receivers dedicated to AIS channels 87 and 88.
I don't have a circuit diagram at hand, but the GX-2150 is a Class D VHF radio so there should be a receiver for voice VHF and a separate receiver for DSC on VHF channel 70; I don't know how they implement AIS reception - it could be a separate, third radio or switch the voice receiver. If Standard Horizon included a circuit diagram in your manual you can fax it to me or scan and e-mail it so I can tell you.

Quote:
Originally Posted by TakeFive View Post
But unlike when you mix and match two devices from two different manufacturers, the GX2150 is designed, tested, warranteed, and reviewed as a single unit, so the complications that you describe are addressed by the manufacturer.
Of course. I haven't done the comparison, but we can look at a comparison of sensitivity and selectivity AND WHERE IT IS MEASURED between single purpose VHF radios and VHF-AIS combinations. It would be interesting. What is clear is that no manufacturer can reinvent the laws of physics. Somewhere in my pile of business cards are some contacts inside Standard Horizon. When I get a chance I'll send them a note and ask for their technical position.

Quote:
Originally Posted by TakeFive View Post
... as a practical matter I've never heard any complaints about the GX2150 having "all the same deficits." In fact, the reviews that I have seen have been overwhelmingly positive. Can you point me to some test results that show that the GX2150 has difficulties hailing dockmasters at marinas?
I can't point to such results because there are few if any side-by-side evaluations in real time and reviews are mostly qualitative anyway. Again, the physics are clear. If you have splitter in your system, internal or external, and have a high-noise or low-signal path then your system will not perform as well as a VHF without a splitter. If you get past the sales people at any radio manufacturer they will tell you the same thing.

Quote:
Originally Posted by TakeFive View Post
As for your suggestion about installing an AIS antenna on the spreader of a small boat, since small boats have short spreaders, the antenna would have to be pretty close to the mast. Wouldn't the presence of the mast so close to the antenna create a blind spot due to shadowing of the signal?
No. Masts and rigging on a single boat have limited impact on field of view. Edge diffraction puts significant energy into the element. Multipath is always a factor, but it's a factor anyway even for masthead antennas. That's different from the effect that we get from hills, buildings, and huge numbers of masts and rigging in a marina.

Nothing is perfect. As many have noted there are compromises in everything. What is very real is that the compromises of a splitter, internal or external, are more significant than most sailors realize.

The place for an AIS receiver to be integrated is in a chartplotter. Many units, especially smaller ones, have already integrated GPS receivers. An AIS receiver would be an easy addition and avoid all the problems of integration with a fixed VHF. If you find one on the market next year remember you heard it here first.
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  #28  
Old 10-24-2013
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Re: VHF AIS radios

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Originally Posted by SVAuspicious View Post
........
The place for an AIS receiver to be integrated is in a chartplotter. Many units, especially smaller ones, have already integrated GPS receivers. An AIS receiver would be an easy addition and avoid all the problems of integration with a fixed VHF. If you find one on the market next year remember you heard it here first.
Wouldn't that mean a PL-259 antenna connection on the chartplotter? To (most likely) an external splitter?? Coupled with the RF issues somehow I don't think any chartplotter manufacturer will be going down that path soon.

Perhaps we can agree to disagree, but to my mind, the only sensible place for an AIS receiver to be integrated is within the radio - VHF+DSC/GPS/AIS together with a single data stream to a non-GPS chartplotter or VHF+DSC/AIS with a data stream to/from a GPS-enabled chartplotter.

Having DSC on the radio is obvious, but having AIS on the VHF, even without GPS, allows push-button "target calling" - not something you can do from a chartplotter.
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Last edited by Classic30; 10-24-2013 at 06:24 PM.
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Old 10-24-2013
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Re: VHF AIS radios

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I hate to admit it, but I got all enthused and have now gone and done a very silly thing....

I've ordered one.
It arrived on my desk this morning, so here's the beastie in the flesh. Quite a compact, neat little unit.. Now to get it installed and see how it performs.

VHF AIS radios-imag0125.jpg
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  #30  
Old 10-24-2013
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Re: VHF AIS radios

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Originally Posted by Classic30 View Post
...Having DSC on the radio is obvious, but having AIS on the VHF, even without GPS, allows push-button "target calling" - not something you can do from a chartplotter.
A couple clarifications here:

Whether your radio has AIS or not, you really should connect a GPS to it (either a chartplotter or, if you don't have that, get a puck like the Garmin 18x LVC). With GPS connected, any DSC calls will transmit your location, including (especially) distress calls that you place with the panic button. It's an important safety feature.

Also, for those who have VHF/AIS combination radios, feeding GPS has the added benefit of enabling the radio to prioritize the AIS targets from closest to farthest, which greatly helps in crowded areas. The GX2100/2150 also have a rudimentary graphical display that shows the targets on your screen, and allows you to select which boat to query or call. But that also requires the GPS signal because it needs to know where your boat is relative to the other AIS targets.
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