Owen Duffy wrote:
Is this the antenna described at http://www.qsl.net/w5dxp/G5RV.HTM ?

Nope, that's just an off-the-shelf vanilla G5RV.

In that article, ...

Forget that article which only shows why the *standard* G5RV is
a fairly well matched antenna on 80m and 40m.

Presumably when you say that the capacitor improves the VSWR on 75m,
you mean the VSWR on the coax. Did I miss something, how does the
capacitor improve the VSWR on 75m?

I'm sure you know this already. Given an SWR circle on a Smith Chart
that crosses the horizontal resistive line at less than 50 ohms and
given the 1/50 conductance circle, those two circles will cross at
two points. Where they cross in the capacitive reactance region is
the point on the transmission line where a parallel capacitance will
bring the impedance at that point to 50+j0 ohms. This is a common
matching technique for 75m mobile antennas. The same thing can be
done with a coil installed where the circles cross in the inductive
reactance region. This technique is described in the ARRL Antenna
Book.

What I have done on my G5RV is find the point where the SWR circle
intersects the 1/50 conductance circle in the capacitive reactance
region on 3.8 MHz and install a 1000 pf parallel cap there. My series
section line is 22.5 ft. of Wireman #554 at that point. The 50 ohm
SWR is reduced from about 5:1 to 1.3:1 on 3.8 MHz.

Given an SWR circle crossing the 1/50 conductance circle, there's a
point where a cap will result in 50 ohms. A little farther, a cap
will result in 300 ohms. A little farther, a cap will result in
450 ohms, etc. These are the points just past the current maximum
point where one can hang a capacitive stub to achieve a purely
resistive impedance.
--
73, Cecil http://www.qsl.net/w5dxp