A question that we often come across at Marine Supply Dock is whether or not a Marine VHF antenna will work with an AM/FM stereo/radio setup. To answer this question simply, in most cases an AM/FM radio will be able to implement existing VHF antennas, given that you buy a Shakespeare VHF AM/FM splitter (separator) as well. That’s the simple answer.
To begin, nearly every boat on the market has a Shakespeare split antenna system setup in combination with the standard VHF antenna. When selecting a VHF antenna for a water craft, it’s helpful to understand the basic concepts of marine antennas. The average size of a VHF marine antenna is 8ft and made out of fiberglass. Shakespeare is by far the most popular company that deals in marine antennas, though they are not the only manufacturer. Decide on an antenna that will fit the size of the craft (e.g. larger vessels require longer antennas, while a fishing boat only needs the standard-sized antenna), decide what range of signal needed, for what type of waters will the craft be used, DB gain, and lastly where the antenna can be mounted.
Length – The longer the length, the farther and greater the range; the rule for sailboats is to have a 3-5 feet mounted on the masthead. However, the 8 feet on the stern is also an option. It simply depends on personal preference. Powerboats require a much longer marine antenna, from 16’-25 feet long. Make sure that the height you choose will clear any of the low bridges or limitations in your area. Keep in mind the following formula:
Where height is above water in feet and the resulting value is range in miles.
Example: Your boat is 7 feet above water. You attach an antenna that’s 3 feet so that’s a total of 10 feet above water. The square root of 10 is 3.16. 3.16 times 1.42 is 4.49 miles. This is the reach of your own antenna. Another boat similar to yours with a reach of 4.49 will make it possible to communicate when you are 10 miles away.
DB gain – Gain is a term that is used to describe the distance measured of transmitted distance. A short sailboat with a whip antenna will have a 3 dB gain while a longer antenna mounted at the same height with a focused transmission (tighter beam) will result in less power wasted and a longer transmission. Smaller ships require lower gain to compensate for heeling angles.
Types of water – Calm waters are the most conducive for signal strength, though that is not always the case.
Mounting location – Find the best location at the highest point on the boat for the best reception/signal strength. Three options available are the mast mounting, surface mounting, or rail mounting. Rail mounting is offered in a variety of sizes that allow for easy lowering, while mast mounting is for sailboats and surface mounting encompass a range of vertical or horizontal surfaces to mount on. This mount also is a mount that allows for easy lowering.
When correct marine antenna has been located, simply find that model number you’re considering and check up the integrity of the antenna. By integrity, I mean find customer reviews for that product so that if there are any ingrained flaws, you can avoid that antenna.