> Today I put a folded Marconi antenna on the air on 40
meters. The unit is fully vertical made out of #14 insulated
house wire spaced 3". I feed my antenna with rg6u. I
found out about my antenna in a book by Bill Orr called
vertical antenna where this antenna and several simular
antenni are described in some detail. Also the radio
handbook by Bill Orr shows this antenna for 160 and 80
meters made out of twin lead. This is a half wave antenna
folded back on itself, a quarter wave high. The far end is
grounded at the feed point, and one should use radials. He
claimed the radiation resistance is 60 ohms. Shown also in
the arrl handbook in the quarter wave verticals section ,1
of the 4 antennas pictured. The arrl picture shows it
having a 150 ohm feed point. There is also a 3 wire version.
Important to remember!
Radiation resistance does not change when the element is
folded. At least not the useful IRE definition of radiation
resistance. Feed impedance changes, but not radiation
resistance by real useful definitions of radiation
resistance.
Ground current does not change, so ground loss does not
change.
Efficiency of the system basically does not change, other
than the fact the thicker element might reduce the almost
meaningless copper losses in the antenna element.
Noise on receiving won't change.
Bandwidth will get a bit better because the element is
fatter.
73 Tom
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|