A little trick for the ground plane...find some AL tape (HVAC guys use it) and use a couple of strips at the base of the antenna. The COAX Shield would connect to the tape (a lockwasher with a tab for connection of a ground plane is common in a Ham's antenna toolbox), while the center conductor would feed the "Whip" part of the antenna. . The tape can be inside a wood bulkhead or under fabric. you will also see this called a counterpoise. Even better is copper tape. two pieces about 2 foot long will help. Look at QSL.NET for a calculator for the ground plane and the antenna length. It will show a length of 1.98 ft for 118.00 mhz, and a radial base of wires or tape, etc. also at 1.98 ft ea. Lots of ham shops have replacement whips for cutting to length for a specific frequency...Look for a "HamFest" in your area and you will be able to get stainless whips enough to support 4-5 airplanes for much lower than a commercial antenna. As Jim mentioned, the rubber duck is a poor antenna....it is "easy" on the operator, one reason those are popular, but a standard 1/4 wace or 5/8 wave whip with a counterpoise will improve the situation. The yagi or quad would only be good on a ground station....you want an omni directional antenna in an airplane, just wanted to clear that point. As an omnidirectional antenna emits energy equally in all directions (and thus receives equally in all directions), it takes more power to get the same level of signal at the same distance as opposed to a quad or yagi, which points more power in one direction. Thus the comment that it would be usable for the initial application mentioned, which was to contact a flight of aircraft in one area for coordination purposes. Think of a megaphone....if you are to the side of one, you hear normal volume....but in front of it is different....all the sound is focused in the direction of the horn. Same principle as a yagi or quad antenna. As for HT antennas, Jim hit the nail on the head...a piece of welding rod is better than a rubber duck. (heck, the nail would be a better antenna...!)

Derswede
Derswede