> Philip Wylie wrote: > > > Here is a second page of thoughts on the topic from my friend. > > [snip] > > > 2. As to the exact length to cut the wire, there are useful formulas in the Radio Amateur's Handbook or the ARRL Antenna Handbook. My copy is in storage so I can only guess at the formula. Something like: for a quarter-wave: > > > > Length in feet equals 496 divided by the frequency in MegaHertz; > > > > So let's see, at 174 MHz, a quarter-wave is 34-1/4 inches long. (IF I remembered the correct formula!) Final trimming to length is best done using the VSWR meter and a pair of cutters. Contact your neighborhood ham radio operator. They are usually eager to help. > > I like to work metric: 3*10^8 m/sec divided by 1.74x10^8 Hz = 1.724 meters > > I.e., divide 300 by the frequency in MHz. > > A quarter wave is then 1.724 / 4 = 0.431m = 43.1cm = 16.96 inches. > > But...that's for a quarter wave in free air. Electricity moves slower in a conductor, so we multiply that by the velocity factor, about .97 for small wires (I posted an incorrect figure earlier) so we multiply and get 16.96 x .97 = 16.45". > > Whew. > > So there's your quarter-wave dimension. > > > 3. A quarter-wave antenna must have a "counterpoise" of another quarter wavelength. Normally this is provided by the metal in the body of the handy-talky (or the roof of your car etc.). An elevated antenna must provide a counterpoise up there in the air. Hence, the dipole antenna - two quarter-waves, fed from the center conductor and the sheath of the coaxial cable. A ground plane can also be used. > > Correct. It is important to note that different antenna configurations have different feedpoint impeadances, and will present diferent loads to the radio.Rather than take up more bandwidth, I invite paddlers with specific questions about making an antenna to contact me and I'll do my best to answer. -- ---------------------------------------- Michael J Edelman mje_at_mich.com http://www.mich.com/~mje http://www.mich.com/~mje/kayak.html http://www.mich.com/~mje/scope.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/ ***************************************************************************
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