Home |
Search |
Today's Posts |
#11
|
|||
|
|||
Antenna for Marine VHF
In article , rickman wrote:
I think the real problem is this antenna for 2 meter operation is 20 feet long! Yup. Great for side-mounting on a tower, so-so for top-mounting on a tower or mast (it'll sway in the breeze and this can wear out the solder junctions), not so great for vehicle mounting, and downright impractical for a hand-held :-) For marine VHF it can't be used on shore, so hanging it from a tree would not work. When you say using a single half wave section wouldn't be much different from a marine VHF antenna, what type of antenna would a marine VHF antenna be? I thought they used a colinear design. For "shortened" antennas, what you'll often find is that they're "loaded" antennas. You can significantly shorten a radiating element, and still have resonance, by adding an inductor of some sort - the shortened element has capacitive reactance, and the inductor's reactance (equal magnitude, opposite sign) cancels it out. One way to do this is to wind the element itself into a spiral... this adds inductance and lets you use a longer piece of wire (i.e. something close to a quarter-wave). Most "rubber duck" antennas are of this sort - they often have an inductor in the base (right by the radio), and the whip consists of a wire wound spiral-fashion around some sort of insulating core. If you buy a hand-held marine-VHF radio, that's very likely what you'll get. An example: http://www.gandermountain.com/modper...ntenna&i=91538 Note they call it "Heliflex" - probably shorthand for "helically wound flexible". It's only 1' long. http://www.gandermountain.com/modper...ntenna&i=91513 This one is 6', or almost 2 meters. It might contain some sort of center-fed dipole (fed up through the center of the lower element), or it might be sort of the equivalent of a J-pole (half-wave or 5/8-wave radiator with a matching stub or coil at the bottom). |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Marine antenna ?? | Antenna | |||
Marine 2m Antenna wanted | Antenna | |||
help with a marine antenna | Antenna | |||
FA: CB ANTENNA M'CYLE-MARINE-BOAT>ANTENNA SPECIALIST MR306 | CB | |||
Is it a CB or VHF marine antenna? | Antenna |