VHF antenna questions

Ok, I know that VHF is line of sight and taller is better, but I have a 18ft bass boat that I will be keeping in the Tampa BAY area so I should never need more than 5 miles of distance to transmit. How short of antenna can I get away with??

I already have a 10 ft. one but it is big and in the way while we fish on this 18ft bass boat. I want the smallest I can with the most distance w/o spending a ton of money.

Re: VHF antenna questions

Check http://members.toast.net/boatguy/vhfant.htm
They state distance is the square root of (height x 1.42). Gain and antenna type also have an effect.

Re: VHF antenna questions

The VHF Marine Band antenna set up I recommend is shown in this article:

VHF Marine Band Antennas For Small Boats
by James W. Hebert
http://continuouswave.com/whaler/reference/VHFAntenna.html

VHF communication is not limited to line-of-sight paths, however paths which are not line-of-sight will have considerably more path loss than those paths which are line-of-sight.

The formulas mentioned above are presumably for calculation of the radio horizon. The radio horizon is normally longer than the optical horizon due to refraction of the radio waves in the atmosphere. The normal correction factor is to assume the radius of the earth is four-thirds (4/3) the actual radius. There are many approximations proposed for the radio horizon calculation. The website cited above is not particularly authoritative and contains several errors. For a more reliable discussion of radio horizon see:

http://en.wikipedia.org/wiki/Radio_horizon

For a discussion of antenna patterns and how they change with gain, see

http://continuouswave.com/whaler/reference/antennaVertical.html

Re: VHF antenna questions

Too many variables to aswer this one. These include current yaw and roll of the boat, wave height(remember these will all change the antennas height, as well as the focus of the TX beam), and most importantly the receiving stations antenna height.

Bigger is better, stick with a QUALITY 8ft antenna with 6db gain. Use a good ratchet mount and fold it down when not using it, or when fishing.

Bill