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Old 05-16-2013, 04:58 AM   #1
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Unhappy VHF Antenna

Hey Guys,
So I need to purchase a new VHF Antenna because mine is MIA (either stolen or broke off).
I forget the length of my old one and have no clue on what a good size/brand antenna would be.
The wire portion is still attached to the mount but the whole fiberglass support antenna is missing.
Does anyone know the correct length antenna for my 94 2700SCR?
Any suggestions on brands or appropriate pricing?

Thanks,
- Joe
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Old 05-16-2013, 12:01 PM   #2
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Hi Joe,
when it comes to antennas you pretty much get what you pay for. Performance comes from a taller antenna (I perfer 8 ft), which is proportional to it's range (distance it can send and recieve). Of cource several 8 footers are sold with increasing price and these give you better connectors which have less lost at the connection. I think the biggest bang for the buch is height. where it's mounted on the boat also come into play. If you mount it on top of an arch then a shorter antenna will give the same performance as mounted lower if the tips are the same height above the water. it's all about line of sight.
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Old 05-16-2013, 01:46 PM   #3
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Ditto^^^^

VHF is line of sight. The higher the antennae is off of the water the farther a signal can be sent/recieved. An antennae 5 feet off the water has about a 3mile sghitline to the horizon. Two boats with an antennae 5 ft. off the water can communicate up to 6 miles. Here is a cool calculator. The "Station" is a boat or land in our case.

http://www.qsl.net/kd4sai/distance.html

The most common is an 8 ft. antennae and Shakespear is probably the most popular. Obviously you can't mount the thing 20 ft. in the air and running with a 20 ft. antennae is not feasible. So there are going to be limits. you should also be considering the Gain, which is measured in DB and indicative of the signal strength, with the higher db gain having theoretically more signal strength.

Here is a good link on what to consider in a VHF antennae:

http://www.westmarine.com/webapp/wcs...e=VHF-Antennas
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Old 05-16-2013, 04:17 PM   #4
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Shrew is correct that gain is important, however since the antenna is passive (no internal amplification) the gain is a result of the antenna's size and losses. Looking at the 8 foot antennas on the westmarine site you will see they are 6dB. Another thing to remember is in rough seas as your boat rocks the transmit/receive distance will be impacted. Since most of us boat within site of shore a 8 foot antenna should provide good coverage in any conditions satisfactory for small craft.
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Old 05-16-2013, 07:12 PM   #5
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Quote:
Originally Posted by shrew View Post
VHF is line of sight. The higher the antennae is off of the water the farther a signal can be sent/recieved. An antennae 5 feet off the water has about a 3mile sghitline to the horizon. Two boats with an antennae 5 ft. off the water can communicate up to 6 miles. [/URL]

Last time on Lake Powell I hailed the marina to get a tow sent out for a stranded boat. The marina was over 40 miles away and not line of sight. My 8' antenna is about 12' off the water. Reception was perfect too.
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Old 05-16-2013, 10:06 PM   #6
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Phillbo,
that marina must have had it's antenna way up on a mast to transmit 40 miles, also no terrain obstacles (hills between you and the marina). You can get extended range from the signal being reflected off hills and heavy low clouds but signal strength is impacted. Another possibility is they are using a high power transmiter/receiver which isn't unheard of for a land base station.

Anyhow must have been a long day for the if the tow boat came from the marina runing at 40 mph (1 hour to reach stranded boat) and over 6 hours to return to marina if towed back there at 6 mph.
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Old 05-16-2013, 11:06 PM   #7
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You're probably right...
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Old 05-17-2013, 01:51 AM   #8
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Right or wrong sounds like we all agree that an 8 foot antenna is the right way to go for most applications.
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Old 05-17-2013, 06:42 AM   #9
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Awesome, Thanks for the help guys.
I think I'm gonna go with this one:
http://www.overtons.com/modperl/prod...3&merchID=4006

Specifications
Finish Fiberglass
Height 8'
Element Copper Cable
Ferrule Chr Brass
Cable 15' RG-58
Gain 6db
Max 50
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Old 05-17-2013, 07:30 PM   #10
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Quote:
Originally Posted by mmwjr View Post
Phillbo,
that marina must have had it's antenna way up on a mast to transmit 40 miles, also no terrain obstacles (hills between you and the marina). You can get extended range from the signal being reflected off hills and heavy low clouds but signal strength is impacted. Another possibility is they are using a high power transmiter/receiver which isn't unheard of for a land base station.

Anyhow must have been a long day for the if the tow boat came from the marina runing at 40 mph (1 hour to reach stranded boat) and over 6 hours to return to marina if towed back there at 6 mph.
Yep, that is how the Coast Guard is able to communicate out so far as well.
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