Radiating Efficiency
 

Reg, this whole thread started because bizarre things happen with
Radial_3 with short radials.

You can go ahead and put a caveat in it if you like, but it's wrong at
short lengths and that fact needs to be made clear to users of the
program, before they install a radial system of 120 2m radials on 80m
and find that it's a terrible ground system.

The question that I want answered is how to optimize my radial system,
and I think at this point, I shall be consulting a document entitled
"Maximum Gain Radial Ground Systems for Vertical Antennas" by K3LC.

Anyone have other suggestions for sources of material for optimum
radial selection given a certain length of wire?

73,
Dan

Reg Edwards wrote:
Frank, I am not interested is what happens at very short lengths or
what Radial_3 makes of it.

To determine Zo, start around 10 metres.

If very little happens to input impedance between 10 and and 15 metres
then you already have Zo = Zin = Ro + jXo.

Neither am I interested in efficiency or antenna input impedance..
The problem of Efficiency has already been sorted out.

etc.

Radiating Efficiency
 

The question that I want answered is how to optimize my radial system,
and I think at this point, I shall be consulting a document entitled
"Maximum Gain Radial Ground Systems for Vertical Antennas" by K3LC.

Anyone have other suggestions for sources of material for optimum
radial selection given a certain length of wire?

73,
Dan

Rudy Severns' article; "Verticals, Ground Systems and Some
History", in the July 2000 QST, is worth a read.
Available on the ARRL web site, or, I also have the pdf.

Frank

Radiating Efficiency
 

To determine Zo, start around 10 metres.

If very little happens to input impedance between 10 and and 15 metres
then you already have Zo = Zin = Ro + jXo.

Neither am I interested in efficiency or antenna input impedance..
The problem of Efficiency has already been sorted out.

All I wish to know is Zin = Zo of a single radial, at various lengths
greater than about 10 metres, of diameter = 1.64mm, depth = 25mm,
ground resistivity = 150 ohm-metres, permittivity = 16, at a frequency
of about 8.07 MHz.

That is the input impedance of one radial when the attenuation is
about 20dB or greater.

To summarise, I wish to know Zo = Ro + jXo for one radial.


Reg, the radial impedance rapidly converges to 101.6 + j 21.1.

10 m -- radial Z = 102 + j 20.99
12 m -- radial Z = 101.3 + j 21.1
14 m -- radial Z = 101.65 + j 21.32
16 m -- radial Z = 101.7 + j 21.1
18 m -- radial Z = 101.615 + j 21.1
20 m -- radial Z = 101.61 + j 21.11

Frank

Radiating Efficiency
 

Reg, the radial impedance rapidly converges to 101.6 + j 21.1.

10 m -- radial Z = 102 + j 20.99
12 m -- radial Z = 101.3 + j 21.1
14 m -- radial Z = 101.65 + j 21.32
16 m -- radial Z = 101.7 + j 21.1
18 m -- radial Z = 101.615 + j 21.1
20 m -- radial Z = 101.61 + j 21.11

==============================================
Frank,

Excellent results! The radial has already converged on Zo = 102 + j21
at a distance of 10 metres. Just where Radial_3 predicts it should.

The magnitude of Zo is within 20 percent of NEC4 and the impedance
angle is in the right ball-park with the correct sign.

Now work downwards from 10 metres, to about 7.5 metres, the 3/4-wave
resonant point, to find the point where Zin has truly diverged from
Zo. You will have to work in gradually smaller increments.

Could you go down to the 1/2-wave resonant point at about 4 metres?

You will now be able to see what I'm heading for.

By the way, how much hard labour is all this causing you? Don't try
to tell me what you are actually doing because I havn't the foggiest
idea.
----
Reg,

Radiating Efficiency
 

I've explained this to Reg many times before, but somehow it doesn't
seem to sink in. Here's the explanation again.

Reg Edwards wrote:
"Frank's" wrote
W7EL tells us that EZNEC doesn't display the surface
wave which obviously contains power. Would that affect
the efficiency using the integration technique?
======================================

The surface or ground wave is the most important fraction of total
radiated power.

It's important only to AM broadcasters and others communicating at low
frequencies, and to HF operators interested in working distances of only
a few miles. At HF, it decays to a negligibly low value within a few
miles, and so is no importance at all beyond that distance.

The correct radiation pattern of a vertical antenna
shows maximum radiation along the ground. Angle of maximum radiation =
0 degrees.

Let's consider that for a moment. The surface wave decays rapidly. So
the "correct" radiation pattern as described by Reg changes dramatically
with distance. At HF, the pattern at one mile will be strikingly
different from the pattern at 20 miles; the first will be maximum at
zero elevation angle, the latter won't. So if you want this kind of
"correct" pattern, you'll have to specify the distance from the antenna.
Once you're a few miles away, at HF, the pattern becomes constant with
distance, because the surface wave has decayed to essentially zero. Then
you have the pattern which is useful in determining communication beyond
a few miles. (This is the pattern reported by EZNEC and NEC as the "far
field" pattern.) Reg's "correct" pattern isn't useful for anything but
short distance communication, and isn't valid except at the distance
specified.

When deducing efficiency, to omit power radiated along the ground from
the hemispherical integration will result in serious error.

Well, it kind of depends what you lump in with losses when calculating
efficiency. The classical formula for antenna efficiency, Rrad/(Rrad +
Rloss), generally applies only to the antenna itself and near field
losses such as ground system losses. So power in the surface wave is
considered to be "radiation", and if you want to calculate this
efficiency by dividing the power in the radiated field by the power from
the sources, you would have to include the surface wave in the
calculation. However, for people communicating more than a few miles,
the surface wave power, which is dissipated in the ground within a few
miles of the antenna, is just as lost as power dissipated in the wires
or the ground system. So if you consider "radiated power" to be power
radiated beyond a few miles and "loss" to be the rest, then you can lump
the surface wave power into the "loss" portion. If you do that, the
efficiency is correctly reported by EZNEC or NEC's average gain function.

( Efficiency by NEC4 ) / ( Efficiency by formula ) = 0.38

I won't comment on that because I haven't a clue where it came from.

I can imagine other losses in addition to loss in the radials but to
have the other losses several times greater is a bit much. Where are
these large losses? Are they in the soil surface - the only other
candidate?

The surface wave power is indeed dissipated in the soil within a few
miles of the antenna.

Roy Lewallen, W7EL

Radiating Efficiency
 

Roy, there you go again - confusing the issue by re-stating the
bleeding obvious.

What happens to the ground wave AFTER it has been radiated is not
relevant to the efficiency problem. ( Which has now been sorted out
anyway.)

The losses we are concerned with all occur in the near field. They
are -

(A) Loss in the radials and loss in the soil in the vicinity of the
radials, which is represented by Rradials. It is the input resistance
of the radials. It can be determined by measurements. Rradials is the
value used in the usual formula -

Efficiency = Rr / ( Rr + Radials ), which, in the present context,
is incorrect.

(B) Loss in the soil surface and soil NOT in the vicinity of radials,
but still in the near field, represented by Rsoil.

Frank, using NEC4, has managed to seperate losses A and B although not
the resistance of Rsoil.

So, after finding a value for Rsoil, a more accurate formula is -

Efficiency = Rr / ( Rr + Radials + Rsoil )

Where Rr is the radiation resistance referred to the base of the
antenna.

Note that Rsoil cannot be measured but can be deduced from the actual
efficiency. Both Rradials and Rsoil are functions of the same soil
characteristics.
----
Reg,

Radiating Efficiency
 

On Sat, 29 Jul 2006 08:10:13 +0100, "Reg Edwards"
wrote:

Efficiency = Rr / ( Rr + Radials ), which, in the present context,
is incorrect.

Hi Reggie,

Of course it is incorrect, it is a definition of your own invention.

Efficiency = Rr / ( Rr + Radials + Rsoil )

This is merely an elaboration of the commonplace
Efficiency = Rrad / ( Rrad + Rloss )
which you declared
is very much in error.

The error is yours, and your bafflegab that has flowed from this
pronouncement of an "error" has been in an effort to cover your
tracks. The wonderment you are met with is that you failed to
acknowledge that Rloss is commonly accepted to mean more than Ohmic
loss.

Reggie, the archive is rich with this discussion, and no one but
yourself makes the mistake of presuming Rloss has ever meant to be
confined to the Ohmic loss of the radiator's metal parts.

73's
Richard Clark, KB7QHC

Radiating Efficiency
 

On Sat, 29 Jul 2006 11:03:36 -0700, Richard Clark wrote:

On Sat, 29 Jul 2006 08:10:13 +0100, "Reg Edwards"
wrote:

Efficiency = Rr / ( Rr + Radials ), which, in the present context,
is incorrect.

Hi Reggie,

Of course it is incorrect, it is a definition of your own invention.
snip

Hi Reg,

By any remote chance have you read any of the posts that followed the one you
initiated in 'radial attenuation', just below the one we're in now?

If not, please do so, and then savor the crow on your plate concerning your
somewhat 'stiff' position on BLE's failure to determine the ground
characteristics that lie beneath the radials.

Thank you.

Walt, W2DU

Radiating Efficiency
 

On Sat, 29 Jul 2006 16:37:05 -0400, Walter Maxwell
wrote:

[snip]

....... then savor the crow on your plate ......

Thank you.

Walt, W2DU

Ah yes Walter, crow on the plate I have had the misfortune of tasting
that old bird on many occasions. I found it very tough and not at all
palatable. G

Danny, K6MHE

Radiating Efficiency
 

"Reg Edwards" wrote in message
...


Reg, the radial impedance rapidly converges to 101.6 + j 21.1.

10 m -- radial Z = 102 + j 20.99
12 m -- radial Z = 101.3 + j 21.1
14 m -- radial Z = 101.65 + j 21.32
16 m -- radial Z = 101.7 + j 21.1
18 m -- radial Z = 101.615 + j 21.1
20 m -- radial Z = 101.61 + j 21.11

==============================================
Frank,

Excellent results! The radial has already converged on Zo = 102 + j21
at a distance of 10 metres. Just where Radial_3 predicts it should.

The magnitude of Zo is within 20 percent of NEC4 and the impedance
angle is in the right ball-park with the correct sign.

Now work downwards from 10 metres, to about 7.5 metres, the 3/4-wave
resonant point, to find the point where Zin has truly diverged from
Zo. You will have to work in gradually smaller increments.

Could you go down to the 1/2-wave resonant point at about 4 metres?

You will now be able to see what I'm heading for.

By the way, how much hard labour is all this causing you? Don't try
to tell me what you are actually doing because I havn't the foggiest
idea.
----
Reg,

This is fairly trivial Reg. It takes me about 90 seconds to run
the program, analyze the data, and record the results for
each length. I consider this a learning experience. Some
of your requests have forced me to read the NEC manual
and other books I have on modeling.

As a preliminary run I have gone overboard, just to see the
overall trend. The fact is I see nothing dramatic happening
until the radial gets very short. Possibly you can see
regions where I need to concentrate. Obviously most of the steps
are very large, and I may have missed something. I would have
expected to see a phase reversal though.

9m Zin = 101.8 + j 21.7
8m Zin = 100.5 + j 21.5
7m Zin = 100.5 + j 19.0
6m Zin = 105.1 + j 17.8
5m Zin = 110.5 + j 26.1
4m Zin = 97.0 + j 40.2
3m Zin = 70.5 + j 25.9
2m Zin = 67.2 + j 19.6

I did try steps of 0.1 m from 8 m to 6.7 m, and saw nothing
but a progressive trend.

Frank