VHF Antenna Question

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Giggitoni

Giggitoni

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Joined
Jun 21, 2008
Messages
2,098
Location
United States
Vessel Name
Mahalo Moi
Vessel Make
1986 Grand Banks 42 Classic
I’m going to replace one of my ancient VHF radios. I’m probably going to purchase a radio capable of receiving AIS. Should I get an antenna that is engineered for VHF as well as AIS? Like the Shakespeare 5225-XT-AIS?
 
Last edited:
If your radio is that old it probably would be a good idea to get a new antenna. Won't hurt and reduces the odds of future trouble.
 
I intend to replace the old antennas. However, I was wondering if an antenna which is marketed for AIS reception and well as regular VHF communication is necessary or better.
 
We had a couple of boats with AIS receivers in the Standard Horizon radios. We experienced good results with the single antenna on both boats. I don't think the antennas were specified for AIS specifically.

We fitted Pacific Aerials antennas and I thought the transmission quality was exceptional. The range afforded by these antennas was much greater than I would have believed if I were not testing it myself. The price was also very attractive.

I have no affiliation with Pacific Aerials beyond being a happy user.

Best Wishes
 
AIS uses marine VHF frequencies. A combo radio such as the S/H GX2200 only uses one good VHF antenna.
 
Normal performance out of a standard vhf antenna for a receive only vhf with AIS on my boat.

It is hooked to the Shakespeare Vhf 17'6" 5018 antenna.
 
For a AIS receiver,a vhf antenna will be fine. It's claimed that for an AIS transceiver, an antenna that is specifically tuned for the frequencies higher on the vhf spectrum ,the ones that AIS use, will to a better job of transmitting. I personally haven't seen that much difference between a quality VHF antenna and a AIS-only antenna regarding transmission.
I have an AIS transceiver on a 5' pacific aerial antenna and a AIS receiver built into the standard horizon 2150 vhf radio that is using a shakespeare 5201 8' antenna. Both receive targets satisfactorily.
 
I have it both ways.

My charter boat has a stand alone Simrad AIS with its it's own Shakespeare antenna mounted on a 10' antenna mast. It's a flawless system that picks up freighters at 50+ miles on the ocean. The key to great AIS (and VHF) reception is a high gain antenna mounted as high as possible.

My trawler has a Icom VHF that passes through a Garmin AIS unit to a 17' Shakespeare antenna mounted off my upper deck. It to is a flawless system. The VHF works great and has clear reception and broadcasting. The AIS also works flawlessly. Was able to pick up freighters on the Great Lakes at over 50 miles last summer.

My conclusion is that with a good antenna setup is essential, and there seems to be no reduction in performance for a modern AIS and VHF sharing the same antenna.

Ted
 
The frequencies used by AIS are so close to those used by marine VHF that an antenna specifically tuned for AIS is not required. Most especially not for a receive-only system. If you were broadcasting AIS you might get a teeny-tiny bit of extra range out of an antenna made specifically for the AIS frequencies. Still, the reality is that an "AIS specific" antenna is pretty much just a marketing gimmick. Any marine VHF antenna will work more than adequately for AIS.
 
I have a receive only AIS that I have never installed. If I can use my VHF antenna then what splitter should be used. I have a vague idea how to do this but would appreciate some advise.
 
Thanks, everyone! My gut feeling has been confirmed.
 
Gulf Comanche said:
I have a receive only AIS that I have never installed. If I can use my VHF antenna then what splitter should be used. I have a vague idea how to do this but would appreciate some advise.
Click to expand...

Many AIS units have a pass through. The AIS has an input and an output or antenna connection. That's how mine is set up. Can't help you if you need an external splitter. There's probably information about this in your AIS installation manual.

Ted
 
I think getting the antenna up higher will have the greatest benefit of all the things you can do.


AIS just uses a couple of reserved channels in the VHF band, so a VHF antenna will work just fine. I think all an "AIS" antenna does is tune to the center of a narrower portion of the VHF band, and empty your wallet a bit more. Your money is probably better spent on an extension pole.
 
twistedtree said:
I think getting the antenna up higher will have the greatest benefit of all the things you can do.


AIS just uses a couple of reserved channels in the VHF band, so a VHF antenna will work just fine. I think all an "AIS" antenna does is tune to the center of a narrower portion of the VHF band, and empty your wallet a bit more. Your money is probably better spent on an extension pole.
Click to expand...

Thanks, Peter.

It’s time to replace my VHF antennas. They are probably 25 years old and are beginning to shed shards of glass on everything that comes close! The base of an antenna is about 14 feet from the water surface which gives me adequate range for the type of boating I do.
 
A passive splitter put in a VHF transmission line will reduce receive and transmit power by about 3 dB or 1/2. The effect of this will be seen mainly on the transmit side as your power output. The cheapest AIS "splitters" are passive. An active splitter requires power and have a wide range of prices. They will also reduce effective power but not by as much. Vesper Marine claims to have a splitter that offers gain, but that is only on the receive side. What this all means, you can buy an antenna or buy a splitter. An antenna might be a better investment for not much more money.

Tom
 
Shakespeare recommends against the use of a splitter for AIS/VHF.
 
Before marketing "invented" AIS antennas we all used vhf. Never had a problem.
 
SoWhat said:
Before marketing "invented" AIS antennas we all used vhf. Never had a problem.
Click to expand...

AIS is a relatively new tool. I was there at the beginning and It was a game changer in any busy harbor I was moving oil barges at the time in NY and it cut down "security" calls by at least 50%. Nobody could "lie" about their position anymore to take advantage of oneway traffic.. I don't remember if seperate antennas were required or not. This is around 1999-2000.
 
Antenna height and low loss cable (RG-8, not RG-58) will make the greatest impact on reception. The Galaxy series of antennae includes the low loss RG-8 cable. :thumb:

Be sure to install the connector as recommended with solder on the core at the PL-259 connector. I've seen folks who don't and regret it years later with corrosion and signal degradation.

(I have a solder gun onboard it you need it. For one IPA, I will solder it for you.)
 
FlyWright said:
Antenna height and low loss cable (RG-8, not RG-58) will make the greatest impact on reception. The Galaxy series of antennae includes the low loss RG-8 cable. :thumb:

Be sure to install the connector as recommended with solder on the core at the PL-259 connector. I've seen folks who don't and regret it years later with corrosion and signal degradation.

(I have a solder gun onboard it you need it. For one IPA, I will solder it for you.)
Click to expand...

Two antennas will cost me four IPAs (two for each). I don't want you to drink alone.
 
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