Outstanding, Reg. Your formula for Rrad agrees completely with the graph in
Devoldere's book. I will make a special effort to copy the formula down
correctly and put it in the subdirectory of my hard disk that has all your
other programs.

I already figured out the 1/4 wave transformer problem, so I went out in
measured again directly (18" jumper) the feedpoint impedance and got much
more realistic readings.

I recall from reading some of your other posts when people were wringing
their hands about what antenna they could put up in a given circumstance.
You advised the inverted L in the garden. When I started work on this
project (whose goal was a decent DX antenna for 80m), I thought of your
comments on many occasions.

As you noted, I'm doing the 2:1 VSWR bandwidth measurements strictly to look
for the point of diminishing returns on laying the radial field. It is quite
clear at this point that 8 is not quite enough, but 16 should be more than
adequate to get me within 1 dB of the idea.

It has been a fun experiment so far, and an enlightening discussion. Thanks
so much for your formula and other comments. Most helpful.

....hasan, N0AN
"Reg Edwards" wrote in message
...

"hasan schiers" wrote (I'm still waiting for
clarification on your formula, btw)

====================================

There's a mistake in the formula. I copied it incorrectly from my old
notebook.

The wavelength Lambda doesn't come into it. No wonder you asked what
units Lambda is in.

The correct, more simple, formula is -

RadRes = 18 * ( 1 - Cos( 180 * H / ( H + L ) ) ohms,

Where H = Height, L = Length of horizontal section, and the angle is
in degrees.

Your antenna is 45 feet high and 70.8 feet overall length. (It doesn't
matter what the measurement units are. It's just a ratio.)

And so your radiation resistance, at 1/4-wave resonance, is 25.4 ohms,
give or take a few ohms.

The only thing I'm unhappy about is making impedance measurements at
the other end of 55 feet of coax. You need to know the exact Zo and
velocity factor and length of this cable, plus some accurate
calculations. The technique is fraught with error.

Get your hand-held antenna analyser right to the bottom end of the
antenna wire, on the R + jX range, and immediately adjacent to the
focal point of the radials. And hope you don't get interference from
the local, high power, MF broadcast station. But you are already aware
of this and I mention it for the benefit of the lurkers.

I assume you measure SWR only to estimate antenna bandwidth. At the
other end of 55 feet of coax anything can happen to SWR. But if
bandwidth decreases as the number of radials increases then at least
it is going in the right direction. I don't think you will squeeze any
other information out of it.
----
Reg, G4FGQ