>WR4R wrote: .............
>
>Orr states this antenna has an impedance close to 50 ohms and should
>match coax without the need of a tuner. I have tried building this and
>cannot obtain a 50 ohm match and have a lot of reactance using Orr's
>measurements.
>
>Thanks,
>Garry - WR4R
>
>
>
EZNEC says the antenna you described, over a good radial system, should
be resonant at about 2.0 MHz with a feedpoint impedance of about 163
ohms (with some variations depending on wire used). The feedpoint
impedance is also likely to be affected by towers that are close. EZNEC
also says it doesn't resonate on 80 meters.
This antenna performs exactly like an inverted L (which it is). It just
has a different matching network, one that actually takes the impedance
further from 50 ohms than it would have been without the matching network.
Tom's comments, in the referenced link, are accurate on radiation
resistance and ground losses. A vertical folded monopole is exactly the
same as a "non-folded" monopole. With EZNEC you can see that ground
losses are the same, simply by looking at the ground currents for a
folded monopole and a monopole. Same ground currents, same ground losses.
Note: EZNEC is very picky about analyzing closely spaced wires. It
takes a lot of segments to get an answer that is close to real.
Jerry, K4SAV
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|