On 4/25/2017 5:43 PM, Dave Platt wrote:
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).

Interesting. Any idea what the specs mean?

Gain 3dBi
"Marine Gain" 6dB

I know what dBi is, but what is Marine Gain? Is there some reference
antenna they use such as the rubber ducky?

--

Rick C