Best practice for VHF & AIS antenna placement

[hellosailor]

Ah, but that Vesper IS NOT A SPLITTER.

It is a combination of low-noise amplifier AND splitter, and any low-noise amplifier can provide gain. There's no magic in that. Of course, like any splitter it wil lstill require TWO ANTENNAS and all it does is eliminate one coax cable run, up to the point where you install it. (More weight and active electronics to install up the mast.)

And, all low-noise amplifiers require power, so either you'll have to run 12VDC up the mast or it will need a power-over-coax adapter, placing DC on the coax cable and providing more complications. (I'm guessing it requires the extra DC wire run.)

There's no magic in the Vesper, or any splitter.

Now, a combination antenna, one antenna that serves both radios, can simplify things. That's simply a "multiband antenna" for VHF/AIS. And the only drawback to multiband antennas is that they cost a bit more, because there's usually a loading trap or other extra bit of hardware to make the magic happen. And, inevitably, some loss of signal strength to at least one of the bands. If that's small enough, it can be worthwhile. Simplest and most effective solution, although it will still require either a combination radio that has one antenna output, or a splitter ("combiner") to let two devices use the one antenna. Still not perfect--but the least clutter aloft, the least number of extra gizmos to fail.

[DotDun]

Originally Posted by hellosailor

Ah, but that Vesper IS NOT A SPLITTER.



It is a combination of low-noise amplifier AND splitter, and any low-noise amplifier can provide gain. There's no magic in that. Of course, like any splitter it wil lstill require TWO ANTENNAS and all it does is eliminate one coax cable run, up to the point where you install it. (More weight and active electronics to install up the mast.)



And, all low-noise amplifiers require power, so either you'll have to run 12VDC up the mast or it will need a power-over-coax adapter, placing DC on the coax cable and providing more complications. (I'm guessing it requires the extra DC wire run.)



There's no magic in the Vesper, or any splitter.



Now, a combination antenna, one antenna that serves both radios, can simplify things. That's simply a "multiband antenna" for VHF/AIS. And the only drawback to multiband antennas is that they cost a bit more, because there's usually a loading trap or other extra bit of hardware to make the magic happen. And, inevitably, some loss of signal strength to at least one of the bands. If that's small enough, it can be worthwhile. Simplest and most effective solution, although it will still require either a combination radio that has one antenna output, or a splitter ("combiner") to let two devices use the one antenna. Still not perfect--but the least clutter aloft, the least number of extra gizmos to fail.

Huh? Not sure you are looking at the Vesper splitter.

https://www2.vespermarine.com/antennas-splitters

[hellosailor]

Yes, Dot, I was looking at the correct device.

RTFM: Vesper may call it a splitter, but the speedometer in my old riceburner also indicated it could do 140mph and it would not make that even in freefall.

Vesper also go on to point out that it has a low noise amplifier built in, which is how they get gain instead of a loss.

A "splitter" does not include a low noise amplifier, in any conventional use of the term. I could just as easily use Vesper's logic (designed to sell products without confusing the customer) to call a boat a time machine. You get on it today, go for a sail, and voila, IT IS TOMORROW! I've gone into the future!

It is unfair to call that device JUST a splitter. It is way more expensive than a splitter, way more complicated, and yes, perhaps it does more as well. But it ain't a "splitter" anymore than my broomstick is a Louisville Slugger. Or vice versa.

[Jim Cate]

Umm, I won't argue pedantically about what to call the Vesper "thing", but I can assure you that it does NOT require two antennas, and that it does allow use of our existing standard vhf antenna at the masthead to serve both the AIS and the VHF automatically with a single coax to the masthead.

I find it to be a useful and effective means of achieving this end, and that it provides excellent range for both functions.

Jim

[TreblePlink]

The box used to share an antenna between AIS with VHF communications radios is indeed much more than a splitter. It is really closer to being a fast switch.

Both AIS class b and VHF have a transmitter and receiver. To share an antenna without very large and expensive resonant cavity filters, anytime the AIS transmits, it must shut off the connection to the VHF receiver, and when the VHF transmits, the antenna is shut off to the AIS. It cannot work any other way, because transmit energy is far more than the receivers can handle without permanent damage. They timeshare.

They share one standard (usually mast-top) antenna. There is no electronics aloft.

Aside from installing just one antenna, the primary advantage is that both AIS and VHF use the highest and least shadowed antenna - for maximum range and most circular horizontal pattern.

I prefer two separate antennas for redundancy and simplicity. I have a manual coaxial switch that will select what function uses the top antenna.

[Paul L]

Originally Posted by hellosailor

Ah, but that Vesper IS NOT A SPLITTER.

It is a combination of low-noise amplifier AND splitter, and any low-noise amplifier can provide gain. There's no magic in that. Of course, like any splitter it wil lstill require TWO ANTENNAS and all it does is eliminate one coax cable run, up to the point where you install it. (More weight and active electronics to install up the mast.)

And, all low-noise amplifiers require power, so either you'll have to run 12VDC up the mast or it will need a power-over-coax adapter, placing DC on the coax cable and providing more complications. (I'm guessing it requires the extra DC wire run.)

There's no magic in the Vesper, or any splitter.

Now, a combination antenna, one antenna that serves both radios, can simplify things. That's simply a "multiband antenna" for VHF/AIS. And the only drawback to multiband antennas is that they cost a bit more, because there's usually a loading trap or other extra bit of hardware to make the magic happen. And, inevitably, some loss of signal strength to at least one of the bands. If that's small enough, it can be worthwhile. Simplest and most effective solution, although it will still require either a combination radio that has one antenna output, or a splitter ("combiner") to let two devices use the one antenna. Still not perfect--but the least clutter aloft, the least number of extra gizmos to fail.

You might be sure of what this device should not be called, you are clearly unsure of how it is used. it uses one antenna and is mounted below deck, not at the masthead. Vesper is offering a functional piece of gear that meets the needs for many. A two antenna install is a less expensive way to setup VHF and AIS.

[hellosailor]

Jim-
I'm not saying it requires two antennas. If it is using one multi-band antenna, the performance (probably on just one band) will be degraded, and *that's* what the low-noise amplifier can compensate for, providing gain on both bands, beyond what the antennas normally would do.
This is the same concept that is used on cars that have "shark fin" antennas on the roof for the car radio, instead of the old whip antennas or the newer shorter "wound" ships. The concept is valid, it works when done properly.
My disagreement is only with the name. My preference? Would be to just keep the hardware simpler, separate, and redundant. I don't like more silicon critters being able to pull down two systems at once, but that's a personal choice.
Kids use their cell phones (excuse me, smartphones) as flashlights. I still keep a mini light on my keychain, because when I want a light, I DON'T want to involve my phone. Even if it can do the job.

[a64pilot]

Originally Posted by Auspicious

Supposedly according to whom?

Click on the link

[blueazimuth]

Split antenna or dedicated AIS & VHF antennae?
1. The Vesper splitter is said to be both high quality, and expensive.

2. A VHF antenna needs to be mounted as high as possible.
An AIS has no such need.

3. The type of coax typically used for a VHF has significant losses for an AIS, when the latter is connected to a long masthead run.

4. If it is considered essential to use the one masthead antenna for both, then the coax cable should be replaced with a low loss coax cable. This necessitates at least 2 people; 1 or more trips up the mast; pulling the larger low loss cable through the mast; the difficulty of making a good solder joint while at the masthead and buying the more expensive low loss cable. To say nothing of the cost of the splitter.

5. Since an AIS doesn't need to be mounted high, it can be mounted on a bimini, radar arch or sternrail. The installation is much simpler; the short length of low loss coax cable is inexpensive; a splitter is not necessary and last, but not least, you still have a VHF antenna, if you loose the mast.
Seems a no brainer

[DotDun]

Originally Posted by hellosailor

Yes, Dot, I was looking at the correct device.

RTFM: Vesper may call it a splitter, but the speedometer in my old riceburner also indicated it could do 140mph and it would not make that even in freefall.

I think you need to RTFM. This is what you stated, none of which is true!

Please explain the 'TWO ANTENNAS'???

Please explain the 'active electronics to install up the mast'???

Please explain the 'extra DC wire run'????

Originally Posted by hellosailor

Of course, like any splitter it wil lstill require TWO ANTENNAS and all it does is eliminate one coax cable run, up to the point where you install it. (More weight and active electronics to install up the mast.)

And, all low-noise amplifiers require power, so either you'll have to run 12VDC up the mast or it will need a power-over-coax adapter, placing DC on the coax cable and providing more complications. (I'm guessing it requires the extra DC wire run.)

[Jammer]

Originally Posted by hellosailor

Ah, but that Vesper IS NOT A SPLITTER.
It is a combination of low-noise amplifier AND splitter ...

I hope we can all just have a cup of tea (or other beverage of our choice), relax, and continue the conversation.

I think we can all agree that the Vesper device does incorporate several functions, among them that it serves as an antenna splitter for rx, allowing both radios to rx simultaneously, and a switching capability for transmit.

It is my understanding that the low-noise rx amplifier is part of the AIS circuit, and not the VHF (voice) circuit. Therefore, though the Vesper is a good, solid product that makes sense in many cases, it does introduce some insertion loss for VHF voice rx and tx.

There's no magic in that. Of course, like any splitter it wil lstill require TWO ANTENNAS and all it does is eliminate one coax cable run, up to the point where you install it. (More weight and active electronics to install up the mast.)

And, all low-noise amplifiers require power, so either you'll have to run 12VDC up the mast or it will need a power-over-coax adapter, placing DC on the coax cable and providing more complications. (I'm guessing it requires the extra DC wire run.)

There's no magic in the Vesper, or any splitter.

My understanding is that most people install the Vesper near their radios, not up the mast, and rely on high-quality coax between the Vesper and the masthead antenna to minimize losses and noise.

Now, a combination antenna, one antenna that serves both radios, can simplify things. That's simply a "multiband antenna" for VHF/AIS. And the only drawback to multiband antennas is that they cost a bit more, because there's usually a loading trap or other extra bit of hardware to make the magic happen. And, inevitably, some loss of signal strength to at least one of the bands. If that's small enough, it can be worthwhile. Simplest and most effective solution, although it will still require either a combination radio that has one antenna output, or a splitter ("combiner") to let two devices use the one antenna. Still not perfect--but the least clutter aloft, the least number of extra gizmos to fail.

Or an antenna that just has a larger diameter radiating element, theoretically, at least. I wonder whether the Vesper does any matching, or if the mismatch for AIS transmissions is just something that has to be tolerated.

[sailjumanji]

Originally Posted by hellosailor

Ah, but that Vesper IS NOT A SPLITTER.

It is a combination of low-noise amplifier AND splitter, and any low-noise amplifier can provide gain. There's no magic in that. Of course, like any splitter it wil lstill require TWO ANTENNAS and all it does is eliminate one coax cable run, up to the point where you install it. (More weight and active electronics to install up the mast.)

OMG, buddy. You do not understand at all how the Vesper splitter is used. Its one antenna, one coax cable, then split between the VHF and the AIS right where they are both mounted.

Plus the way it works, I believe the VHF either takes precedent over the AIS, or the AIS transmit is so quick it is not noticeable. I have the Vesper XB8000 and an Icom VHF both using the same VHF antenna and the splitter. I have NEVER had any issue with interrupted VHF transmission or reception. You don't even know the AIS is working - although you can see it on the plotter, and I have received calls from other ships and tugs that see me on AIS.

Oh, and why share one antenna? Because this system works, and why not have the VHF and AIS at the top of the mast. Where both of them get maximum range. And take up the space of one antenna.

And I have used this system with a VHF tuned antenna, and the antenna from Vesper that is tuned between the VHF and AIS bands. I noticed no difference in either AIS or VHF performance. And the Vesper combo antenna is a little more than $100, which I don't think is more or less expensive than a decent VHF-tuned antenna.

Amazing some of the comments on this thread, advising how things work. I had to read it twice to really understand that you were commenting about a system that I own and have used almost four years. "The splitter is not a splitter", "two antennas and one coax", "12 volt DC up the mast"! OMG, you have no idea what you are talking about.

To the original poster, I can personally attest - thru four years of ownership and use - that the Vesper XB8000 and Vesper antenna splitter are an excellent combination, perform very well, and I have never had any issues. I have them on my current boat, and am going to put the exact system on the next boat. I don't think there is any difference between two separate antennas, or one with a splitter. In fact, I think you have to get both antennas to the same height to match the performance. And when we cruise, I also carry a spare antenna, and that satisfies my redundancy.

[Paul Elliott]

Originally Posted by blueazimuth

2. A VHF antenna needs to be mounted as high as possible.
An AIS has no such need.

This of course depends on what range you want from your AIS system. But typically you can do with the shorter range you will get from an antenna mounted lower than the masthead. My AIS antenna is on the upper spreader now, but I got adequate performance from an antenna on the stern pushpit rail.

Originally Posted by blueazimuth

3. The type of coax typically used for a VHF has significant losses for an AIS, when the latter is connected to a long masthead run.

AIS and marine band VHF are close enough in frequency that the coax loss (with a properly-tuned antenna) will be about the same for both. For longer runs you want low-loss coax, at least RG8X or better, for both AIS and VHF.

Originally Posted by blueazimuth

Since an AIS doesn't need to be mounted high, it can be mounted on a bimini, radar arch or sternrail. [...] you still have a VHF antenna, if you loose the mast.

And this is a good solution, as long as you have the cables and connectors needed to swap antennas. Often the AIS transponder will use a "BNC" connector, but the VHF uses a "PL259" ("UHF") connector. Since my AIS antenna is on the mast, I carry a spare VHF whip I can clamp to the rail in an emergency.

[Dockhead]

Originally Posted by TreblePlink

The box used to share an antenna between AIS with VHF communications radios is indeed much more than a splitter. It is really closer to being a fast switch.

Both AIS class b and VHF have a transmitter and receiver. To share an antenna without very large and expensive resonant cavity filters, anytime the AIS transmits, it must shut off the connection to the VHF receiver, and when the VHF transmits, the antenna is shut off to the AIS. It cannot work any other way, because transmit energy is far more than the receivers can handle without permanent damage. They timeshare.

They share one standard (usually mast-top) antenna. There is no electronics aloft.

Aside from installing just one antenna, the primary advantage is that both AIS and VHF use the highest and least shadowed antenna - for maximum range and most circular horizontal pattern.

I prefer two separate antennas for redundancy and simplicity. I have a manual coaxial switch that will select what function uses the top antenna.

All this.

AFAIK, that expensive Vesper switch/amplifier works fine and should be a good solution for anyone for whom getting another coax run up the mast is a problem. I don't think most people talk on the VHF so much as to be suppressing important AIS messages, so I don't really think the time sharing is a problem.

The Vesper thing has an advantage over separate antennas in that both radios are using an antenna ideally placed with no rigging, mast, or anything in the way.

However, I prefer separate antennas for redundancy and simplicity, as TreblePlink said. It takes fairly sophisticated electronics to make the Vesper thing work -- something else to fail.

P.S. Concerning HEIGHT of the AIS antenna -- you can see yourself whether any proposed mounting location gives you enough height to send where you want to, to antennas at whatever given height. For 10 to 12 miles even the pushpit would be high enough, but keep in mind that waves can block VHF signals. I have mine 10 meters or 33 feet above the waterline on a low spreader.

[Dockhead]

Originally Posted by Paul Elliott

. . . And this is a good solution, as long as you have the cables and connectors needed to swap antennas. Often the AIS transponder will use a "BNC" connector, but the VHF uses a "PL259" ("UHF") connector. Since my AIS antenna is on the mast, I carry a spare VHF whip I can clamp to the rail in an emergency.

I have adapters for this purpose. I also have an old Bird coax switch which I intended to install but in the event decided I didn't want the insertion loss.

BNC connectors are electrically superior to UHF, but have no weather proofing at all and are flimsy. I wish the industry would ditch the antique and obsolete UHF connectors and go to Type N.