On Wed, 29 Nov 2006 19:33:40 GMT, Owen Duffy wrote:

On Wed, 29 Nov 2006 11:31:01 -0500, John Ferrell
wrote:


Sorry for the confusing terminology but I am confused!

John,

For the moment, forget the term resonance, what it means, what is
resonant, and the importance or not of resonance.

Just make you objective a feedpoint Z = 50+j0.

The testing I have done so far with this 28 foot antenna has been
series fed. The results obtained have been consistant with the Eznec
models.

Ok, I assume that means YOU have created and run the NEC models.

So now model the gamma match, initially with zero capacitance. The
diameters of the gamma arm and and the driven element, and spacing are
critical parameters, change them until you have the desired feedpoint
R. Then insert a capacitor at the feedpoint to offset the inductive
reactance in the feedpoint Z.

Then build it, and see if you can't make it work.


I believe my current direction requires I puzzle out the Gamma match
in Eznec.

That is probably a lot easier than suck it and see experiments.

Owen

PS: When you have done all that and it works, go back to thinking
about resonance, and take a system view. In EZNEC you could explore a
solution for the same operating frequency with a shorter vertical, say
25', design the gamma match for a 50+j0 feedpoint, compare the gain to
the longer model and answer the question of whether natural resonance
of the driven element alone (ie without the gamma arm) is critically
important to performance of the antenna system.
A progress report:
I have not adapted your advice yet and I am going to have to break for
a while to do some real work but here is where I am...
For ease in modeling I have a 2*28 foot (56 ft overall) free space
dipole: This frees me from ground effects. I used #12 wire to simplify
wire intersections. I have NOT experimented with spacing and wire
diameters yet.

I will attempt to attach the Eznec file here in case anyone is
interested.

TIP: to get a better view of the matching setup temporarily change the
lengths of the +28 and -28 wires to 10 feet.
John Ferrell W8CCW