Not vouching for "degree of accuracy", but here's how I estimate efficiency:

(Known Rrad/Measured R at X=0) at the feedpoint.

If my Inverted L has a predicted Rrad of 25.9 ohms and I measure the R at
resonance as 29 ohms, the 3.1 ohms is return loss. This would indicate an
approximate efficiency of 89%.

It seems to me to be a fair approximation. When you have added as many
radials as possible and watched the input R at the feedpoint (at resonance)
drop asymptotically toward the predicted or "known" Rrad, your final "R"
value is used in: Rrad/R. For a perfect ground Rrad = R

I use an MFJ-269 antenna analyzer for the measurements.

Have I gone astray? (aside from my starting value of Rrad, which I took from
two sources: your rule of thumb formula for Inverted L's, and ON4UN's Low
Band DX'ing Handbook). Both your formula and ON4UN agree as to the value of
Rrad for my antenna.

I'll replay to other aspects of your response in another post.

73 and thanks for the new program. As you can tell, I've been playing with
it. As you can also tell, the implications with respect to length of radials
required for good efficiency are causing my brain to cramp.

....hasan, N0AN

"Reg Edwards" wrote in message
...

=========================================
Yes Hasan, good agreement. How did you determine efficiency to THAT
degree of accuracy?
=========================================

Reg,

I think you made a typo...if I go with the shorter 5 metre radials, I have
enough wire to put in 66 more radials, not 20. If I stay with my existing
50' length per radial, then I have enough wire for 20 more.

I have the wire. It won't be used for antennas. I have 200 more lawn
staples, so there is no burying, they are "stapled" to the surface, soon to
fall below the "thatch". My 1000' of copper wire has become too valuable to
let sit on spools in the basement. (In case you haven't noticed, copper
prices have gone through the roof!)

So...I'll be putting down either (20) x 50 ft or (66) x 15 ft radials. Don't
worry about my back. When you have a radial plate and a light hammer,
stringing tons of radials is a piece of cake...paying for the copper (in the
future) is going to generate pain elsewhere.

73,

....hasan, N0AN
"Reg Edwards" wrote in message
...
==========================================
Yes. Use the program to calculate efficiency with the extra 20
radials. Assume all the radials are 5 metres long. But you may not
think the meagre 3% or 0.13dB in efficiency is worth all the labour
and back-ache. By now you are beginning to appreciate how useful the
program is.
==========================================
..
==========================================

Hasan, if I were you I would lay some extra short radials between the
existing long radials - and get some Sloan's liniment to be massaged
into my back. But the increase in efficiency would be un-measurable.
You are fortunate to have very low soil resistivity. Mine is about 70
ohm-metres and for years on the 160m band I have had 7 radials about 3
metres long plus an incoming lead water pipe.
----
Reg, G4FGQ

wrote:
96 radials, 7MHz, antenna height 10.72m. Soil 500ohm*m, permittivity
13\

Radials and antenna 1.024mm (18AWG), radials 3mm deep(surface)
Radial Length, %Efficiency

2m, 93.19%
3m, 93.83%
4m, 92.47%
5m, 86.01%
6m, 80.39%
7m, 85.92%
8m, 89.06%
9m, 89.59%
10m, 88.22%
11m, 85.99%
12m, 85.51%
13m, 86.67%


I sure wouldn't fully trust a NEC based program for buried wires, let
alone a program someone just threw together without any verification at
all. This is especially true when the answer looks so weird. Standing
waves on a wire in contact with soil making efficiency go down as the
wire length is increased? Give me a break!

I seriously doubt any vertical antenna would be even close to 93%
efficient with 7 foot long buried radials.

A precise looking answer that gives us a warm fuzzy feeling makes the
answer a good one, no matter how wrong the answer is.

73 Tom

"Reg Edwards" wrote in message
...
If you are considering a new vertical antenna, instead of guesswork
and copying somebody else's un-thought-out efforts, download program
RADIAL_3 from website below.

The program assists with choosing an economic length and number of
shallow-buried ground radials. It takes a new look at how radials work
by considering them to be lossy, single-wire transmission lines,
open-circuit at the other end.

RADIAL_3 is a self contained file, 55 kilibytes. Easy to use. No
training needed. Download in a few seconds and run immediately.
----
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. .........



That is quite a bold statement and looks like trivilializing, ignoring the
real workings of vertical antennas and radials!

What would NEC4 say?

73 Yuri, K3BU

What would NEC4 say?

Who or what is NEC4?

"Reg Edwards" wrote in message
...

What would NEC4 say?

Who or what is NEC4?

http://en.wikipedia.org/wiki/Numeric...magnetics_Code

You need at least an odd number of 1/4 wavelengths to satisfy the boundary
conditions.
You need at least three to define a plane (or cone, if you want a 50 ohm
feedpoint)

73
H.
NQ5H

That is quite a bold statement and looks like trivilializing, ignoring the
real workings of vertical antennas and radials!

What would NEC4 say?

73 Yuri, K3BU

NEC 4 produces significantly different results. I can provide NEC code
and NEC 4 output files if anybody is interested.

73,

Frank
(VE6CB)

Frank,

How about posting a summary of them, for my example in an earlier post (I
listed all the input values for Reg's program). I'd LOVE to have the data
for my measurement verification!.

If you need the my values I can send them to you for a run. I'd be very
excited to see what NEC-4 says, and use them to validate my measurements.

73,

....hasan, N0AN
"Frank" wrote in message
news:NTLvg.147445$771.19250@edtnps89...
That is quite a bold statement and looks like trivilializing, ignoring
the real workings of vertical antennas and radials!

What would NEC4 say?

73 Yuri, K3BU

NEC 4 produces significantly different results. I can provide NEC code
and NEC 4 output files if anybody is interested.

73,

Frank
(VE6CB)

Frank,

How about posting a summary of them, for my example in an earlier post (I
listed all the input values for Reg's program). I'd LOVE to have the data
for my measurement verification!.

If you need the my values I can send them to you for a run. I'd be very
excited to see what NEC-4 says, and use them to validate my measurements.

73,

Hasan,

I ran a sample model from Cebik's 2nd book, and compared it with results
from Reg's program. The antenna used in the example is a 160 m vertical,
with
four buried radials. The height of the vertical is 40 m, and the radial
lengths
are 40.95526 m. The diameter of the vertical section is 25 mm, and the
radials
2 mm. Ground Er = 20, and conductivity 30.3 mS/m (33 ohm-m). The radials
are buried 0.163821 m (0.001 WL). The test frequency is 1.83 MHz.
NEC 4 shows in input Z of 47.2 + j 14.44 ohms. Max gain 2.11 dBi at
17 degree elevation angle. At the moment I have not figured out how
to obtain the total radiated power from NEC, other than the numerical
integration of the normalized far field data. For a symmetrical pattern
this is fairly trivial using Excel. The model does not include copper
losses,
so this should be added for accuracy. Reg's program computes the
input impedance as 30.35 - j 53.1.

I think I have all the data for your antenna from your previous post. There
may be some difficulty in actually running it in NEC 4 with the parameters
you have provided. The depth of the radials is so small (1mm), in relation
to the wire diameter of 4 mm. Wire junctions must occur at Z = 0,
and the wire diameter must be less than the segment length, which
obviously cannot be met. Also segment length tapering would be
required in order to keep the number of segments at a minimum, and
avoid excessively long run times. In effect your radials are close enough
to be considered laying directly on the surface of the ground. Cebik
does imply this is acceptable in his book, but on his web site
states that NEC 4 becomes unstable with wires in the region of Z = 0.
I assume this also applies to wires below ground. Under certain
conditions wires can approach the ground to within 10^(-6) Lambda
(about 0.1 mm at 3.62 MHz). Based on these constraints I could
develop a model, which will probably be close enough.

73,

Frank