Yep! A question remains for modelling. Is the value for Source Data in EZnec
4.x directly correlated to the Rrad? My EZnec model (a modified ARRL
Inverted L with radials), shows:

Frequency = 3.6 MHz

Source 1 Voltage = 25.65 V. at 4.18 deg.
Current = 1 A. at 0.0 deg.
Impedance = 25.58 + J 1.872 ohms
Power = 25.58 watts
SWR (50 ohm system) = 1.958 (25 ohm system) = 1.081

Is that 25.58 ohms the same 25 ohms from the graph of Devoldere's book, or
is it simply a coincidence?

I have attached my *.ez file, if it makes it through the usenet group.


From my other more recent posts on the topic, you can see that I went back
out to the feedpoint with an 18" jumper and remeasured and the results are
quite "traditional".

If one can believe the graph in the latest version of Devoldere's "Low-Band
DXing", an inverted L like mine withe a .16 wavelength vertical portion and
the horizontal or vee'd portion making of the remainder to achieve
resonance, the Rrad should be about 25 ohms. Since the Z at resonance at the
feedpoint with 8 radials 66 feet long shows 38 ohms, it would appear I have
something like 13 ohms of ground return loss. This would represent an
efficiency of 67% or a loss of 1.7 dB. I'm thinking another 8 radials should
get me closer to about 1 dB of loss, at which point, I think I'll be tired
of cutting slits in the lawn. vbg

I did use an on-line TLE calculator to correct for the 55' of LMR-400, and
doing that yielded readings virtually identical to those I measured at the
feedpoint through my 18" jumper.

So, all in all, things worked as they should What got me confused was not
considering that I had a quarter wave transformer after I moved into the
shack to measure, and it was inverting my readings. Made me real queasy
there for a while.

Thanks to all for taking the time to provide ideas and answers. Tom and a
few others caught the 1/4 wave transformer problem...and after all, that was
my real question. I had no doubt that I was seeing an improvment in
efficiency by adding radials (as the 2:1 BW was steadily decreasing with
increasing radials)...I just couldn't get my head around the 60 ohm, ever
increasing values of Z in the shack. All I can say now is, "DUH!"

The sun has set....it's time to make instant switching comparisons between
my 45' high dipole and the new Inverted L. Last night and this morning it
appeared (although I didn't have a lot of data points yet), that stations
1500 km were much stronger on the inverted L than they were on the dipole,
including a 59+ report from an LU early this morning.

Thanks again, Wes (and all the others who commented). It has been fun
working through the process. Now it's time to chase DX.

....hasan, N0AN
"Wes Stewart" wrote in message
...
On Sat, 3 Sep 2005 09:50:43 -0500, "hasan schiers"
wrote:

I do have correlation now. The vswr meters and the mfj all read the same
resonant frequency now, Wes. See my post that shows the data for 0,2,4,8
radials. While a given absolute value might be in error (a certainty due
to
inexpensive instruments), the trend is sound for bandwidth, but a bit
strange for feedpoint impedance. (BW is narrowing but input Z is going up,
with increasing numbers of radials.)

Ideas?

Well, I think that you're expecting the thing to behave just like a
monopole but it's not a monopole.

When I model your configuration (except for insulation) I get a
resonant freq of 3.573 MHz and R = 23.3 ohm over a Mininec Pastoral
ground.

Making it a full height monopole it must be 67' high and the feedpoint
R = 37.

I believe that I read elsewhere that you are taking data at the input
end of a coax line. Unless you have characterized the line and are
backing out its effects you are going to remain mystified.

Also it you have any other antennas in the area that can be an issue.

I'm a believer in modeling but unless -everything- is accounted for,
reality and the model won't correlate.

For example, I have a Cushcraft AV-80 vertical that I've used as a
test bed. This is a 2" diameter, 36' high pipe with four 3' top hat
wires. Cushcraft supplied a base-loading coil, which is not used.
The antenna is ground-mounted on a 16" square aluminum plate with
sixteen 50' radials. Installing radials at this location is a
"sticky" proposition and the soil is best characterized as sand
(decomposed granite actually).

I have measured the base impedance with both an HP8405 Vector
Voltmeter and coax bridge that was calibrated with an open-short-load
(OSL) method as well as a much faster N2PK vector network analyzer,
calibrated the same way. All measurements were taken at the base of
the antenna. This is an on again off again project (currently off)
with the goal of determining the effectiveness of the radial field.

The data are very repeatable and believed to be correct; however, I
cannot construct a model that replicates the physical antenna. For
example the curve on the Smith chart of the measured data has a little
bump in it and the resonant frequency is slightly off from the model.
The "bump" isn't a full-blown resonance loop, but it looks like it's
trying. Here is a plot from 1.5 to 15 MHz. The resonant freq is 5.5
MHz.

http://users.triconet.org/wesandlinda/Vertical_Z.gif

As you can see from the photo, there several other "verticals" in the
vicinity as well as my 45' foot tower with beam and wire dipoles 90'
away.

http://users.triconet.org/wesandlinda/Vertical_4.jpg