Reg Edwards wrote:

Your programs results also dramatically disagree with Brown, Lewis,
and
Epstein's data in one of the most comprehensive radial studies ever
done.

73 tom

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

All three of B,L & E forgot to determine ground resistivity and
permittivity. That's hardly comprehensive!


Do your predictions fit BL&E's measurements, or those of Sevick, for
*any* assumed values of ground resistivity and permittivity?

Also , please tell us more about the fan of 1.0m radials, on the ground,
that will give ninety-several percent feedpoint efficiency.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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)

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?
=========================================

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)

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

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

"Yuri Blanarovich" wrote in message
...
Reg wrote among other stuff:

You've been reading books and magazines about rules-of-thumb written
by old-wives. At 3.62 MHz and a radial length of 16 metres the
attenuation approaches 100 decibels. So there's no current flowing in
the radials beyond 5 metres. You can remove the excess 12 metres.
They are not doing anything. What small current density there is
beyond 5 metres is all flowing in the soil. The cross-sectional area
of the soil carries the small current just as well as the radials.

==========================================
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.
==========================================

Reg,

NEC4 engine can accommodate on the ground or buried radials in modeling
and calculating vertical antenna parameters and performance.

I bet Roy has his hair standing up, or perhaps still trying to recover
from the "appreciation" of your program, unless he is still running
calculations :-)

You are trivilializing, ignoring 100 years or so of vertical antenna
research, measurements and misleading innocent users of your program. You
might be right in calculating the resonant frequency of piece of wire in
the dirt, but that is far from its contribution to the vertical antenna
performance and efficiency.
You better switch to some better quality vino and read up on the subject.
:-)


Yuri K3BU

Has anybody confirmed the "on-ground" accuracy of NEC 4? Cebik
has published conflicting statements regarding this capability.

Frank

hasan schiers wrote:
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%.

Hi Hasan,

Roy Lewallen and I just measured some ground systems. Actual
measurements using good instruments, not guesses or models.

In one case we had an antenna with four elevated radials that within
measurement error (using lab type gear) had equal signal strength level
as the very same vertical element over 16 buried radials. As I recall
the buried radials had over 60 ohms of base impedance, the six foot
high elevated radials was down around 40 ohms or less.

Over the years I have measured many antenna with very low base
impedance and terrible efficiency, I have measured verticals where
changing the ground system did not change impedance but improved field
strength, and it is very easy to find cases where changes in a ground
system can have MORE efficiency with higher feed impedance without
changing anything but the ground system.

Over simplification of a complex system will often not produce reliable
results. Just look at the results of Reg's progam where it predicts
highest efficiency with very short radials. We all know that doesn't
happen, but the oversimplified program says it does.

73 Tom

"Ian White wrote
please tell us more about the fan of 1.0m radials, on the ground,
that will give ninety-several percent feedpoint efficiency.

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

Ian, you must have had no experience of a few short radials.

Try 16 or 32 radials, 1 or 2 metres long, in good soil, with a 1/4 or
3/8-wave vertical or inverted-L antenna. Radiating and receiving
efficiency will surprise you. Also at all higher frequencies.

At your new QTH you may not find much good soil. But try it anyway.
Or persuade someone else to try it.

I managed for many years with 7 radials 2 metres long, covering an
angle of only 90 degrees. Soil resistivity was only 70 ohm-metres.
Unfortunately, had to abandon it when the garden was turned into a
patio. Damned concrete!
----
Reg.

Reg Edwards wrote:
Try 16 or 32 radials, 1 or 2 metres long, in good soil, with a 1/4 or
3/8-wave vertical or inverted-L antenna. Radiating and receiving
efficiency will surprise you. Also at all higher frequencies.

That sounds like scientific validation of a program or theory, compared
to all the work Brown, Lewis, and Epstein did with field strength
meters.

Maybe that's where S units came from?
S-urprise units?

At your new QTH you may not find much good soil. But try it anyway.
Or persuade someone else to try it.

....and they will be able to quantify what? Emotions?

I managed for many years with 7 radials 2 metres long, covering an
angle of only 90 degrees. Soil resistivity was only 70 ohm-metres.
Unfortunately, had to abandon it when the garden was turned into a
patio. Damned concrete!

I managed with a ground rod. I managed 12 dB better with radials.

Who was it that said if you can put a number on it you don't understand
it? Someone in England I think.

73 Tom