[Antennas] Modeling ground mounted verticals
Red
[email protected]
2004年3月12日 10:48:30 -0600
NEC-2 based models will not calculate impedance of a ground mounted
vertical accurately. Follow the advice in the EZNEC help file. The
calculated value will put you into the ballpark but you end up adjusting
the matching network.
I've used a 20 meter 5/8 over ground radials and it is a very strong
performer. I didn't measure it, just matched it with a "T" matching
network (tuner), because that was conveniently available. An "L"
network will match the antenna with less loss.
My antenna was 30 feet of 3 inch irrigation pipe with a 2 inch section
telescoped into it for a total of 40 feet. Modeling the stepped element
is difficult.
A Gamma feed eliminates the need to insulate the radiating element from
earth ground. I haven't attempted that and am interested in any
guidelines or experience you can offer. I'll start with the guidelines
in the ARRL Antenna book.
I'll put it up again this summer and see if my Autek will measure the
input impedance; if it will, selecting components for an "L" network
will be easy. See ARRL Handbook or Antenna Book for the formulas.
73 de WO�W