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19-01-2018, 09:21
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#1
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,759
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Best practice for VHF & AIS antenna placement
The received wisdom seems to be that the best VHF antenna is a 1/2 wave, center-fed dipole placed at the top of the mast. These don't require a ground plane and have modest gain so that they are less affected by heeling than a higher-gain antenna might be.
What is the best type and placement for a separate AIS antenna on boats with but a single mast?
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19-01-2018, 11:32
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#2
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֍֎֍֎֍֎֍֎֍֎
Join Date: Apr 2006
Posts: 15,136
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Re: Best practice for VHF & AIS antenna placement
If the VHF (regardless of type) antenna is at the masthead, the best place for a second VHF antenna (which is what the AIS really is) would be below the VHF antenna, so there is very little interaction between the two. In practice that probably means mounting it on the spreader, compromising the protected position with the slight interference from the proximity of the mast and rigging.
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19-01-2018, 12:44
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#3
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Best practice for VHF & AIS antenna placement
If your going to use a separate AIS antenna, consider Vesper’s dual antenna that is supposed to work for both. That way you would have a back up VHF if needed, although I believe a regular AIS antenna would work well enough as a VHF antenna.
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19-01-2018, 16:32
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#4
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Registered User
Join Date: Jul 2005
Location: Bellingham
Boat: Outbound 44
Posts: 9,319
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Re: Best practice for VHF & AIS antenna placement
Our AIS antenna is mounted on the Bimini top rail. It works decent at that height. It also doubles as a backup VHF antenna should we loose the mast.
__________________
Paul
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20-01-2018, 09:32
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#5
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Marine Service Provider
Join Date: Nov 2016
Location: Post Falls, ID
Boat: Jeanneau Sun Odyssey 45
Posts: 50
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Re: Best practice for VHF & AIS antenna placement
Is there a specific reason you want a separate antenna? We have a splitter under the nav station for VHF, AIS, and broadcast Radio. It works extremely well and we have very long range AIS and VHF operation in practice. There have been no interoperation issues in the 4 years we have had the boat with this setup.
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20-01-2018, 10:05
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#6
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Registered User
Join Date: Feb 2014
Location: Fort Myers Beach, FL USA; Boston, MA USA
Boat: C&C Landfall 43 and O'Day 35
Posts: 76
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Re: Best practice for VHF & AIS antenna placement
Quote:
Originally Posted by svmobert
Is there a specific reason you want a separate antenna? We have a splitter under the nav station for VHF, AIS, and broadcast Radio. It works extremely well and we have very long range AIS and VHF operation in practice. There have been no interoperation issues in the 4 years we have had the boat with this setup.
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I just had new instruments installed and they did the same thing. A splitter for one antenna to both AIS and the VHS radio. While I was dubious at first, I haven't had any issues. Thanks for the testimonial. I feel better about the config now!
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20-01-2018, 10:32
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#7
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Registered User
Join Date: Dec 2014
Location: Summer Europe Winter Florida
Boat: Dufour Nautitech435/FP Venezia42/Baltec Visiona 40/Catalac 10m used as a river cruiser
Posts: 182
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Re: Best practice for VHF & AIS antenna placement
I would prefer a separate AIS antenna to a splitter as so VHF use does not interrupts AIS.
As the height of the AIS antenna is not very important you may intall that antenna on the Bimini if you have one ore even on the pushpit. My AIS antenna is about 12 feet above the waterline and I received signal from lighthouses 600 NM away.
Good luck
James
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20-01-2018, 12:59
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#8
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Registered User
Join Date: Mar 2011
Location: fl- various marinas
Boat: morgan O/I 33' sloop
Posts: 1,447
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Re: Best practice for VHF & AIS antenna placement
Unless you talk constantly a splitter makes more sense than 2 antennas.
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20-01-2018, 13:45
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#9
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Best practice for VHF & AIS antenna placement
Supposedly a Vesper splitter and one antenna will outperform individual antennas.
https://www2.vespermarine.com/antenna-splitter-sp160
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20-01-2018, 14:55
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#10
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Registered User
Join Date: Feb 2011
Location: Meandering about the Gulf of Alaska coast [NNE Pacific]— where the internet doesn't always shine... [Even Elon's...] Homeport: Wrangell Island
Boat: Nauticat 43 [S&S Staysail Ketch]
Posts: 1,662
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Re: Best practice for VHF & AIS antenna placement
You asked about placement of a separate AIS antenna, which is what we also considered- and we have 2 masts...
Despite the simplicity of putting one of each antenna on each mast, we opted for redundancy [we have 2 fixed VHF radios- one for back-up] and installed a Vesper dual tuned AIS/VHF antenna on each mast head [1 wired to each VHF radio] and a single Vesper splitter. [The splitter can be quickly rewired in the event one antenna and/or connection failed.]
Best wishes deciding what is ideal for your set-up.
Cheers! Bill
This is a very functional set-up for us.
__________________
SV Denali Rose
Learning every day- and sharing if I can.
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20-01-2018, 15:22
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#11
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Registered User
Join Date: Jun 2007
Location: SW Florida
Boat: FP Belize, 43' - Dot Dun
Posts: 3,823
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Re: Best practice for VHF & AIS antenna placement
Quote:
Originally Posted by a64pilot
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And out-cost!
My AIS antenna was <$60 plus ~$30 in coax.
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21-01-2018, 10:34
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#12
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Registered User
Join Date: Feb 2011
Location: Meandering about the Gulf of Alaska coast [NNE Pacific]— where the internet doesn't always shine... [Even Elon's...] Homeport: Wrangell Island
Boat: Nauticat 43 [S&S Staysail Ketch]
Posts: 1,662
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Re: Best practice for VHF & AIS antenna placement
Quote:
Originally Posted by DotDun
And out-cost!
My AIS antenna was <$60 plus ~$30 in coax.
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That is a significant savings, DotDun.
Can you provide the specifics for the rest of us? [Source, product specifications, any reviews or testing results, etc.]
Thanks! Bill
__________________
SV Denali Rose
Learning every day- and sharing if I can.
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21-01-2018, 10:34
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#13
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Registered User
Join Date: Jun 2003
Location: Chesapeake Bay
Boat: HR 40
Posts: 3,651
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Re: Best practice for VHF & AIS antenna placement
Quote:
Originally Posted by a64pilot
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Supposedly according to whom?
__________________
sail fast and eat well, dave
AuspiciousWorks
Beware cut and paste sailors
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21-01-2018, 10:44
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#14
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Registered User
Join Date: Jun 2007
Location: SW Florida
Boat: FP Belize, 43' - Dot Dun
Posts: 3,823
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Re: Best practice for VHF & AIS antenna placement
Quote:
Originally Posted by wrwakefield
That is a significant savings, DotDun.
Can you provide the specifics for the rest of us? [Source, product specifications, any reviews or testing results, etc.]
Thanks! Bill
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https://www.defender.com/product.jsp...062&id=1143468
plus a piece of coax and splice
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21-01-2018, 10:50
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#15
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,759
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Re: Best practice for VHF & AIS antenna placement
Thank you all for the insightful replies.
I note that the Vesper antenna splitter has significant insertion loss on the VHF (voice) side of things -- 1.5 dB on receive and 1 dB on transmit, according to the manufacturer. Whether this is enough to matter is debatable and in practice is going to depend on the situation and other aspects of the installation.
VHF voice is going to be noise limited in a busy harbor and line-of-sight limited in most other cases, but the insertion loss might make a difference in fringe situations where there are intervening obstructions like trees.
Cost wise the splitter, at $249, is about the same, or perhaps a little more money, than a higher quality antenna, mount, and co-ax.
Food for thought.
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