VHF Antenna Location - SailNet Community

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  #1  
Old 05-21-2008
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VHF Antenna Location

I use VHF radio's everyday (pilot) but I have a question.

I have a Catalina 22 which will most likely never sail outside of Biscayne Bay ( SIGH) i.e. not far out at all perhaps 8 miles

Can I get away with a transom antenna mount? For the purposes of cable run etc a transom mount would be much better than a mast head mounting...

Thanks for any and all opinions!
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Old 05-21-2008
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Yes you can get by with it, however higher is better as VHF is a line of sight transmission. You will lose range the lower the antenna.
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Old 05-21-2008
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Sure you can, though your range will be somewhat less than with an antenna mounted atop the mast. It would be good for communication with boats from about 3-4 miles (power boats) and 4-6 miles (other sailboats with mast-top antennas), and shore stations which tend to have towers.

I had a Catalina 22 for years, with a mast-mounted VHF antenna. Great little boat.

Bill
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Old 05-21-2008
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However, if you get into trouble, you'll probably be wishing you had a mast-top antenna, with the much greater range. A mast-top antenna would probably give you 20 miles of reach, versus the 3-6 miles for a transom mounted antenna.
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What the others said: VHF is more-or-less line-of-sight, so height is king. That being said: You can gain a bit of the performance lost to height back with a larger, higher-gain transom-mount antenna. And a transom-mount antenna has the advantages that 1. It's not at the top of that big lightning rod and 2. If you're de-masted, you'll probably still have a (functional) antenna. (VHF ain't worth a warm bucket of spit under water.)

Jim
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One thing to consider with the transom or any antenna really is exposure to RF energy. Mast mount is best, but just make sure others are not near the antenna when you transmit.
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Old 05-21-2008
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If you are thinking about transom because of not wanting to drop the mast:
My buddy and I dropped his catalina 22's mast by hand - set up a crutch on the transom and guidel lines fore and aft. All told it weighs about 200 pounds, three people would have been better. Catalina rigging settings are readily available for when you raise it again.
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Old 05-21-2008
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Dropping the mast

Not too hard. And there are any number of variations on how to do it for a Cat 22. Here's one: https://netfiles.uiuc.edu/rwahlfel/www/GerryStlouis.htm. And you should go to You Tube or other video-sharing sites and get other ideas.

Keep in mind that there are two kinds of VHF antennas. You want one with a globe-shaped radiation pattern, rather than one with a flattened pattern that is "optimized" for longer-distance performance with the same wattage. Reason: sailboats heel, and once an oval-shaped radiation pattern is no longer parallel with the horizon, well then ...
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You basically want a 3 dB gain 3' VHF whip. Looks like this:

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Old 05-21-2008
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Why would you not sail outside the Biscayne bay (not that it's not a beautiful place to sail, if you have to be stuck in one) ?
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