On Sat, 24 Dec 2005 19:21:36 GMT, Lancer wrote:

+On Sat, 24 Dec 2005 18:26:15 GMT, james wrote:
+
+On Fri, 23 Dec 2005 19:30:25 -0500, Scott in Baltimore
wrote:
+
++ I don't think so, only because I have seen flat ground planes. My Starduster
++ were at a sharp angle. Maybe Scott can knows better. I would think the flat or
++ GP at 90 degrees to the center conductor is fine.
++
++Straight radials would create a 30 ohm antenna.
++45 degree droops create about 50 ohms.
++
++There shouldn't be any current flowing down the outside of the
++shield with a groundplane, so you won't need a balun,
++unlike a dipole that requires equal and opposite phases.
++If you try to feed a dipole with coax, the outer shield
++becomes part of the antenna system, causing high SWR readings,
++(even if the SWR is low), RF interference and degraded performance.
+******
+
+At 30 Ohms you will need some matching network to cancel the reactive
+portion out and rasie the radiation resistance of the antenna up to
+that of 50 Ohms. I would not reccomend direct coax attachment even to
+a 1/4 lambda ground plane antenna.
+
+james
+
+So what reactive component does a 1/4 wave monopole have? How much
+loss do I have on my 40 meter 1/4 wave vertical fed directly with RG-8
+coax? Should I put a coil or capacitor at the feedpoint of my
+vertical?
****

Lancer there is only one real solution for an antenna that will match
a 50 Ohm feedline. That is when the antenna is 50 + j0 Ohms. Or 50
Ohms resistive. There are an infinite number of complex solutions
that will yield a magnitude of 50 Ohms impedance. What solution yours
is will be totally unique to your location and installation. No way
for me to predict that. Therefore there is no way that I can predict y
our losses. Either from load reflections as well as radiation
efficiency of your antenna. Then again if the magnitude of the
imedance of your antenna is 30 Ohms then you may choose to live with
the reflections in the transmission line as well as any looses due to
inefficiency do to the actual radiation resistance what ever it is for
your installation.

Loss in an antenna, that is radiation efficiency, is dependant on the
radiation resistance of the antenna. This also sets the Q or quality
factor of the antenna. That is the bandwidth in which there is
reasonably efficiency of the antenna (70.7%).

Actually a coil or capacitor is best inserted in the radiator. Choice
of base load or loads at other locations are for another discussion.
The reactive component value will mainly depend on the physical length
of the radiator and its reference to lambda.

james