[Antennas] Home Brew Portable Vertical Antenna

2002年9月22日 07:59:26 -0400

Hi All,
I am making a home brew portable vertical antenna. It will be 16'+ long 
and have two elevated 1/4 wave radials. It has an insulator at 8' and a 
shorting bar so I can configure it for 10 or 20. I want to put a bug 
catcher coil around the insulator and tune it for 30 or 40 meters. Can 
anyone tell me where I can find a good, high Q bug catcher antenna coil 
that I can install around the insulator, and use a tap for 30 and 40"? The 
insulator is about 1" in diameter but the coil would be larger in diameter 
and supported by the top element. The assembly doesn't have to withstand 
80 MPH winds, as it is portable.
Anyone have any design information on such an antenna? I was planning to 
calculate the inductance of the loading coil, then model it using 
EZNEC. Then tune it using my Autec VA1. The radials will be cut from a 
length of 5 wire rotor cable. I was planning to make the radiating element 
about 1' short and the radials about 6" long each to broadband it a bit and 
raise the radiation resistance to about 50 ohms. The Xl of the radials 
will cancel the Xc of the radiating element, and will avoid one radial 
hogging most of the current which it will tend to do if the radials are at 
resonance and thus near zero impedance.
Anyone have any idea what the 40 meter configuration performance of the 
antenna tuned for 40 but operated on 15 would be?
I'm looking for suggestions before I start cutting wire, etc.
TNX,
73, Chas, W1CG
K2 #462