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Old February 15th 06, 06:31 PM posted to rec.radio.amateur.antenna
Cecil Moore
 
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Default 300 ohm folded dipole from ARRL Handbook, early 1990's

Geoffrey S. Mendelson wrote:

Hi, the early '90s ARRL handbooks had construction information for a
simple folded dipole made of 300 oHm twinlead. The article was not in
the '96 edition or later.


I have the '93 edition and cannot find it but I remember how to
do it.

The antenna was made of 300 ohm twinlead. It was fed in the center by
a 300 ohm twinlead feeder to a matching capacitor which made it aproximate
50 ohms. The capacitor could be either a regular capacitor (I used silver
mica WWII surplus) or a "stub" of more twinlead.


Assuming the SWR on the 300 ohm twinlead is 1:1,
you want to install a capacitor that causes an SWR of 6:1
on the twinlead between the capacitor and the 1:1 choke/balun.
300+j0 in parallel with 0-jXc needs to result in 60-j120 ohms.

The reactance of the capacitor should be -j150 ohms and it should
be positioned 0.062 wavelength from the 1:1 choke/balun. For instance,
for 7.2 MHz, the capacitor should be 147pf and be positioned
7.7 ft. from the 1:1 choke/balun assuming a VF of 0.9.
--
73, Cecil http://www.qsl.net/w5dxp