Antennas a a fascinating study, and over my 36 years in electronics I have not lost interest in it. My decision regarding N13333A is that it will have a 1/2 wave dipole in a 1/4 wave vertical ground plane configuration fro the VHF comm system. It will be removable so I can adjust and maintain it as required for best radiation. It will have a good ground plane at a 135 degree angle to the main antenna for a 50 ohm feedpoint impedance.
(antenna impedance = 36 ohms if the groundplane is at a 90 degree angle to the vertical antenna, 50 ohms (the desired impedance ) if the groundplane is bent down another 45 degrees (for an angle of 135 degrees from the main antenna element) and 73 ohms for a dipole ( that is a 1/4 wave main antenna with a groundplane element at an angle of 180 degrees from the main element.). That last bit of trivia explains why the dipole in the plane has been working well: The angle from the main antenna in the tail to the lower element in the boat has been closer to 135 degrees. That explains at least one aspect of the current antenna configuration. BTW, being practical: there is really only a negligable difference in practice between antennas with these angles. I will be using a Balun at the antenna to decouple any RF currents from the coaxial shield. This will also reduce the risk of interference to any other system in the plane. (important) The last thing I will be doing is using a length of LMR 400 or LMR-600 for the feed line. Its heavier, but it also has far less loss than RG-58 or RG-8X. (remember that even 1db of loss is about a 20 percent loss) (important) Of course N1333A is fiberglass. You guys with all carbon fiber have another altogether different issue. Current builders should plan for antenna areas to be fiberglass or kevlar, and take the ground plane into consideration. One last bit of news: I am about Two weeks out from taking my Written PPL test, and less than 20 hours flying time to my Practical. Lots of reviewing and very little sleep. Wish me luck. :-) Glenn Martin Owner KR2 N1333ABiloxi, MS, 39532 rep...@martekmississippi.com
