"Jeff Liebermann" wrote in message
...


... The length of the wire between the coax
connector center conductor and the driven element is an inductor. In
order to tune out this inductance, one needs a series capacitor, with
the inductor and capacitor tuned to the operating frequency.

Yes.

I've been making copper pipe and 2-wire transmission line J-poles for almost
20 years. With pipe, I usually fasten the two feed points with clamps and
slide the connections up and down. I'll get a VSWR low-point in-band but
early-on, I discovered that the best VSWR was often about 1.7:1. I had read
about (but never built) a gamma match, so I'd heard about the series cap to
tune out the inductance. I tried a series cap at the feed and it helped.

70 - 100 pF seems to be about right at 2m and I can often get a 1:1 reading
somewhere in the band. Does such a 0.3 dB improvement matter? That's not
my call. When I'm essentially playing with the technology, I can take more
time than if I'm working, like to a deadline or a budget.

"Sal"