CAUTION CAUTION CAUTION:

The wire segments are NOT equal in this model. Frank is sending me a new one
with linear segments. I'll correct the errors below as soon as I get the new
values.

....hasan, N0AN

"hasan schiers" wrote in message
...
Preliminary numbers from Frank's NEC-4 run on Reg's model below:

Caveat: I have not been able to ask Frank if the segments are all the same
length along the radial wire. The info below is based on that assumption.

The radial is 10 meters long, buried about 1 inch. I'm reading the numbers
from the graph that Frank sent me. The radial wire is 40 segments long or
.25 meters per segment. The antenna is 9 feet long and modeled at 8.07
mhz.

If I'm reading it right, at 30 segments along the radial wire, the current
has dropped from a peak of 0.6 amps to 0.2 amps. 30 segments seems to be
7.5 meters out. If the current is still 0.2 amps at 7.5 meters out on a 10
meter radial, then Reg's approach fails. He indicated 20 dB down at a
short distance out. 75% of the way out on the 10 meter radial, the current
is down 0.2/0.6 = .33. 10log * 0.33 = 4.8 dB (if I did that right).

So...it seems that the current along the radial is down only 4.8 dB at 75%
of it's length. Reg indicated that it should be down 20 dB at about 1/3 of
its length.

At the 35th segment of the radial, the current is 1/6th or 7.8 dB down.
This is at 90% of the radial's length.

At the 39th segment of the radio the current is .025 amps. 0.025/6 =
.0146. 10log * .0146 = 14 dB down. That is only 14 dB down at 100% of the
radial length.

I'm using 10 log * (I1/I2) for for the dB calcs...I think current ratios
and power ratios are 10log, and voltage is 20log.

It is possible I'm interpreting Frank's graph incorrectly or applying the
attenuation that Reg refers to incorrectly. I'm just so glad to see some
numbers for current distribution along a radial wire from NEC-4, that I
had to post what I see.

Eyeballing it looks like thisthe radial wire starts at segment 39 and
runs to segment 79)

Segment 39 0.60 amps, distance from source = 0, dB = 0
Segment 49 0.54 amps, distance from source = 2.5 meters, dB = 0.46 dB
Segment 59 0.42 amps, distance from source = 5.0 meters, dB = 1.5 dB
Segment 69 0.22 amps, distance from source = 7.5 meters, dB = 4.3 dB
Segment 79 0.025 amps, distance from source = 10 meters, dB = 14.8 dB

What does Reg's program predict for dB down on this sample antenna?

Using 25 and 25 for soil and the info Frank gave me:

Reg's program shows radial attenuation of 20 dB at 2.3 meters from the
source.

Side by side with the NEC-4 data

Distance Reg NEC-4 (dB down)

2.5 m 21.2 0.46

5.0 m 42.4 1.5

7.5 m 63.9 4.3

10 m 83.3 14.8


These numbers are so far apart, it looks like I did something terribly
wrong. Someone please correct me.
Keep in mind these are preliminary attempts to analyze the NEC-4 based
graph that Frank sent me. I really do hope I did something wrong.

...hasan, N0AN

"Reg Edwards" wrote in message
...
Frank,

Just to confirm we are both working on the same system, I have -

Number of radials = 36
Length of radials = 10 m
Diameter of radials = 2 mm
Frequency = 7 MHz
Antenna height = 9 m
Antenna diameter = 1.64 mm = 14 AWG
Ground resistivity = 150 ohm-metres
Ground permittivity = 16

IMPORTANT:

If NEC4 gives you the input impedance of the radial system I should be
very pleased to know what it is.

Otherwise we shall have no idea where the discrepancy arises - in the
radial system or in the antenna efficiency calculation.

Radiating efficiency is estimated by my program by the well-known
formula -

Efficiency = Rrad / ( Rrad + Rradials )

provided antenna and radials reactance are tuned out.

Whereas NEC4 calculates efficiency by integrating power flow over a
hemisphere WITHOUT tuning out antenna and radials reactance.
Altogether different.
----
Reg, G4FGQ