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