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Steve Chillcott's notes on the radio antenna August 2010 The type of straight antenna we use on aircraft need to have the load balanced by a groundplane to be most efficient. If you have a metal aircraft this is taken care of by the ali fuselage but in a wooden or composite aircraft you need to provide that ground. The best way of doing it for an aircraft is to make a metal plate that you screw the earth side of the coax cable to and from that have 4 radials about 25-30mm wide and 56-57cms long. If your antenna length is 57cms you will be tuned to the center of the aircraft vhf band. The measurements go from where the coax cable joins to the end of the piece of metal. The radials ideally would be 90degrees apart giving a square pattern below the antenna and sloped down at 45 degrees but you just have to do what you can with the space you have available. This tricks the system into thinking there is a larger ground area below it. If you can get an SWR meter and connect it in line with the transmitter you should have a reading of 3:1 or less ideally around 1.5:1 if you can when you transmit. You can adjust the lengths of the antenna and groundplanes to improve this a bit. The problem with a high SWR is that some of the energy that goes from the radio gets reflected back from the antenna if it cant get out and reduces the efficiency of the transmitter and in extreme cases can actually damage the output transistors. Think of it as a tap on the end of the coax that cant be opened fully. If you have no form of groundplane and you have a simple whip antenna I suspect you will have a very high SWR causing radio problems
From Jo McCollum Feb 2007 - Radio Antenna Make 2 strips from 12X3 mm alloy 6060T5 or similar Make them 485 mm long fit them vertical with a 15mm spacing. Then fit RG-58/U coax cable with round ends crimped to the inner and outer wire fit one cable to the top alloy strip and one to the bottom strip see the drawing and the photo it would be possible to fit this antennae inside the fin or rudder out of sight. I fitted this to my Menestrel after many different types of experimenting and this has given me the best radio ever its perfect for wooden or composit aircraft. The drawing below can be obtained from Joe as a more readable PDF file. Below that are more pictures.
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