Cecil Moore wrote:
john doe wrote:

Is it possible to cancel the capacitive reactance of the antenna by
placing an inductor in series with the radiator??


That's exactly what happens with the 5/8WL vertical and
base coil.

coil 5/8 WL
GND---/////////--------------------------------------
^
|
50 ohm tap

The coil and 5/8 WL whip form a series-resonant circuit.
--
73, Cecil http://www.qsl.net/w5dxp

Not quite. If you look at the analysis I posted regarding the tap feed,
you'll see that the inductive reactance required for feeding the antenna
this way isn't equal to the series capacitive reactance of the antenna.
They're often close (as in the example, where the feedpoint series X =
-300 and the required Xl = 319 ohms), but how close they are depends on
the Q (Xs/Rs) of the feedpoint Z. When you feed the antenna this way,
what you have is not a series resonant circuit but a parallel resonant
one, and the required inductance is different for the two. The
requirement for this type of feed is not series resonance, but that the
Z at the top of the coil be completely resistive, which series resonance
doesn't produce. As I pointed out in my most recent posting, you can
make a series resonant circuit consisting of the antenna and an
inductor, and put the source in series with that. But you need a
different size inductor.

Roy Lewallen, W7EL