RadioBanter - View Single Post

December 1st 05, 07:01 PM posted to rec.radio.amateur.antenna

wrote:

I'm wondering
if a short vertical with long elevated radials would result
in an "off-center-fed" vertical.

Not the way I see it, just as long as all the radials are
equal length. The reason I don't see it, is the radiation of the
radials should pretty much cancel if all are equal. Not
quite the same as the single radial in that situation.
If you had one radial, maybe so...

I just ran one on EZNEC. The feedpoint is at 23 feet and there
are four 23 foot radials drooping at 45 degrees. (I already
had this one modeled.)

With a 23 foot vertical section, the feedpoint resistance is
56 ohms on 10.2 MHz. 234/10.2 = 23 feet

With a 12 foot vertical section, the feedpoint resistance is
84 ohms on 16.4 MHz. 234/16.4 = 14.2 feet, 2.2' longer than 12'.

It looks like (with slanted radials that radiate) there is an
"off-center-feed" effect, i.e. longer radials require a shortened
vertical section.
--
73, Cecil, http://www.qsl.net/w5dxp