Dave Kruger wrote: > ...Antenna modifications (even a telescoping whip) > are a liability on the water, owing to the strong likelihood salt water > will enter the radio and ruin it, unless the unit is completely enclosed > in a *durable* plastic shroud.) The antennas supplied with most radios attach via a BNC connector which is not a watertight fitting. If the radio is waterproof with the supplied duckie, it'll be waterproof with any other antenna. > 2. I got no detectable improvement *in transmissions* using a whip > adjusted to a length apropos for the marine VHF band. How did you measure this? You can't go on percieved strength of the received signal since FM tends to be all-or-nothing over a wide range of signal strength. You need to either measure the strength of the received signal or do a range test over unobstructed ground or water. > I was warned, by > the highly-regarded marine radio shop from which I bought my ICOM, that > an incorrect antena configuration could *damage the radio.* I own a > commercially-made dipole on a 6-foot piece of coax which can be tuned to > the marine VHF band, and hung vertically from a tree (or paddle, etc.). > I think this should improve performance, but have not been able to test > it yet. A ham sent me some terrific plans for a "narrow beam" antenna > I'd like to try out, but that will have to wait. Narrow beam aka high gain antennas aren't a good choice for seaborne use unless you're in an actively stabilized boat ;-) The antenna must be properly oriented to take advantage of the narrow radiation pattern. A simple whip can be made from a BNC connector, a length of music wire and a plastic bead to protect one's self from the pointy end. It *will* have a great advantage over a rubber duck; duckies are very lossy and can have less than ten percent of the efficiency of a simple whip. A half-wave marine antenna mounted on the deck will have even better efficiency. The advantage of a duck is that it's compact and not in the way if your radio is clipped to your PFD. But if you're in the water holding your radio in your hand just above the water you're not going to have much useful range anyways. Then again, from reading Ralph's writings on navigating in traffic the single best use of a hand-held marine radio might for short range transmissions. "Calling BEHEAMOTH! There is a small, flimsy kayak DEAD AHEAD of you!!!!!" The marine shop that gave you the warning about damaging the radio is not really correct. Typical modern radios have foldback protection that limits output into an improper termination. You can't make a hand-held radio otherwise, since a few inches movement of the radio near the body results in gross differences in the actual impeadance of the antenna system, which is to say you're always transmittting into a mistuned antenna system. Another reason why getting the antenna away from the paddler helps. I don't have a VHF marine radio so all my testing has been with amateur VHF, but the physics are the same. -- Michael Edelman http://www.mich.com/~mje Telescope guide: http://www.mich.com/~mje/scope.html Folding Kayaks: http://www.mich.com/~mje/kayak.html Airguns: http://www.mich.com/~mje/airguns.html *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Wed Mar 04 1998 - 09:35:35 PST
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