Length & number of radials again
 

Radials Continued.

Perhaps some kind person who has been able to afford the latest issue
of NEC4 could calculate the radiating efficiency of a typical vertical
antenna of height 9 metres (29.5 feet) and diameter 50mm (2 inches) -

- when fed against a ground system of 50 uniformly distributed radial
wires, each 1.64mm in diameter (14 AWG) buried to a depth of 25mm (1
inch), of length 10 metres -

- in soil of typical resistivity = 150 ohm-metres and permittivity =
16.

But first I should like to ask, can NEC4 complete such a calculation
without human intervention or assistance? If yes then please
continue, perhaps keeping a record of the time involved.

Using program RADIAL_3 the answer is - Radiating Efficiency = 86.0
percent.

If several of you participate, perhaps using different tools, it would
be interesting to compare results. By all means, join in!

Thank you for your assistance.
----
Reg, G4FGQ.

Length & number of radials again
 

"Reg Edwards" wrote in message
...
Radials Continued.

Perhaps some kind person who has been able to afford the latest issue
of NEC4 could calculate the radiating efficiency of a typical vertical
antenna of height 9 metres (29.5 feet) and diameter 50mm (2 inches) -

- when fed against a ground system of 50 uniformly distributed radial
wires, each 1.64mm in diameter (14 AWG) buried to a depth of 25mm (1
inch), of length 10 metres -

- in soil of typical resistivity = 150 ohm-metres and permittivity =
16.

But first I should like to ask, can NEC4 complete such a calculation
without human intervention or assistance? If yes then please
continue, perhaps keeping a record of the time involved.

Using program RADIAL_3 the answer is - Radiating Efficiency = 86.0
percent.

If several of you participate, perhaps using different tools, it would
be interesting to compare results. By all means, join in!

Thank you for your assistance.
----
Reg, G4FGQ.

Reg, I made some changes to the antenna, but should not effect
the result too much. The maximum number of junctions without
a workaround is 36, so I reduced the number of radials to 36.
Ok, I know that give 37 junctions, but doubt it will effect the
result. I changed the vertical diameter to #14, since I
had a warning with the 25 mm diameter. Again there are
workarounds, but I did not want to spend all day figuring
out segmentation and length tapering.

You did not specify the frequency, but assume from the
dimensions it is 7 MHz. I used 7.000 MHz. The input impedance is
27.33 - j 109 ohms. Since I am only learning how to use the program
I don't know if NEC can provide the total radiated power. I
computed the total radiated power by summing power density over a
hemispherical region. For 100 W input I get a total radiated power
of 30.5 W. It took me 90 minutes.

Regards,

Frank

Length & number of radials again
 

Reg Edwards wrote:
Perhaps some kind person who has been able to afford the latest issue
of NEC4 could calculate the radiating efficiency of a typical vertical
antenna of height 9 metres (29.5 feet) and diameter 50mm (2 inches) -
- when fed against a ground system of 50 uniformly distributed radial
wires, each 1.64mm in diameter (14 AWG) buried to a depth of 25mm (1
inch), of length 10 metres -

Would it help to model this in EZNEC with the radials 1/1000
of a wavelength above ground?

Just heard a funny line on Stargate SG-1 on TV:
"This planet is as dead as a Texas salad bar."
--
73, Cecil http://www.qsl.net/w5dxp

Length & number of radials again
 

"Cecil Moore" wrote in message
y.net...
Reg Edwards wrote:
Perhaps some kind person who has been able to afford the latest issue
of NEC4 could calculate the radiating efficiency of a typical vertical
antenna of height 9 metres (29.5 feet) and diameter 50mm (2 inches) -
- when fed against a ground system of 50 uniformly distributed radial
wires, each 1.64mm in diameter (14 AWG) buried to a depth of 25mm (1
inch), of length 10 metres -

Would it help to model this in EZNEC with the radials 1/1000
of a wavelength above ground?

Just heard a funny line on Stargate SG-1 on TV:
"This planet is as dead as a Texas salad bar."
--
73, Cecil http://www.qsl.net/w5dxp

Ground planes above ground can approximate the results
from buried radials. The wires should be several wire diameters
above the ground, and not 10^(-6) wavelengths -- providing
that a finite ground, Sommerfeld/Norton method, is used.
The reflection coefficient approximation will produce large errors.

73,

Frank

Length & number of radials again
 

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

Length & number of radials again
 

Frank wrote:
Ground planes above ground can approximate the results
from buried radials. The wires should be several wire diameters
above the ground, and not 10^(-6) wavelengths -- providing
that a finite ground, Sommerfeld/Norton method, is used.
The reflection coefficient approximation will produce large errors.

Here's what the EZNEC manual says: "Horizontal wires should not
be placed exactly on the ground, but should be at least 1/1000
wavelength above (and in the case of EZNEC/4, also below) the
ground."
--
73, Cecil http://www.qsl.net/w5dxp

Length & number of radials again
 

Here's what the EZNEC manual says: "Horizontal wires should not
be placed exactly on the ground, but should be at least 1/1000
wavelength above (and in the case of EZNEC/4, also below) the
ground."

Cecil, Probably the 1/1000 WL limit contains a safety margin.
This does not appear to be addressed by either the NEC 2,
or NEC 4 user manual.

Cebik's book "Intermediate Antenna Modeling", p 1-12,
states: "The minimum height for wires above
a Sommerfeld-Norton ground has two dimensions. The first
relates the height above ground limit to the wire radius.
The wire height (h) should be several times the wire radius
(a), that is, h~a. As well, the minimum height is related to
the wavelength for the frequency in use:
(h^2 + a^2)^(1/2)10^(-6)Lambda. If a is very small
compared to h, the wires may approach 10^(-6) Lambda
toward ground. ......reflection Coefficient approximation....
.... the general recommendation is that ......
horizontal wires should be () 0.4 Lambda above ground".

Obviously, from the manual quote, EZNEC can invoke a
Sommerfeld-Norton ground.

Since I do not have GNEC I usually test my NEC 4 models
with NEC-Win Pro. Interestingly NEC-Win Pro actually
runs, with no errors, on below ground wires. The results
are usually pretty weird though.

73,

Frank

Length & number of radials again
 

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.

Correct Reg, Those are the parameters I used, with the
exception that the radials were also # 14 AWG (1.64 mm).

You raise some interesting points -- How do I measure
the radial impedance? I have to think; given a vector
network analyzer, how would I measure a radial system
under laboratory conditions? this is what I need
to replicate with NEC. Since I have never made
such a measurement, I am not sure where to begin.
Would it be valid to consider one radial wire as
an "End fed zepp", and feed one end with an
ideal transmission line? As long as I know the current,
and voltage at the measurement point, I can determine
the input impedance -- problem is; voltage input
with reference to what?

As for the reactive input; this is of little concern to
NEC since it drives the load from a complex
conjugate source.

So far as I have been able to determine NEC does
not provide the total radiated power, only the
normalized far field in peak "Volts" -- i.e. V/m at
1 meter, at every angular increment. Usually
every degree. I take these data to determine the
power density at each increment, and sum
over a hemispherical region; where I take the
elemental area to be:
(r^2)*sin(theta)*d(theta)*d(phi). Since the
pattern is symmetrical I only need 91 points.

Frank

Length & number of radials again
 

Frank,

So NEC4 cannot calculate input impedance of the radial system and we
have almost reached a dead end.

Would it be possible to insert a loading coil ( 2.48 uH ) at the
bottom of the antenna to tune out its input reactance ( which is what
my program does.)

Then repeat the efficiency calculation and tell me what you get.
----
Reg.

Length & number of radials again
 

Frank,

So NEC4 cannot calculate input impedance of the radial system and we
have almost reached a dead end.

Would it be possible to insert a loading coil ( 2.48 uH ) at the
bottom of the antenna to tune out its input reactance ( which is
what
my program does.)

Then repeat the efficiency calculation and tell me what you get.
----
Reg.

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

Alternatively, or in addition to, you could shift frequency nearer to
8.3 MHz where the antenna is resonant and its input reactance is zero.

And again do the efficiency calculation. Tell me what the efficiency
is and the frequency. Also the antenna input resistance.

You will see I am desperately trying to localise the discrepancy in
efficiency. It is either in the radials or in the antenna. You should
also learn something about NEC4.
----
Reg.

Length & number of radials again
 

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

So NEC4 cannot calculate input impedance of the radial system and we
have almost reached a dead end.

Would it be possible to insert a loading coil ( 2.48 uH ) at the
bottom of the antenna to tune out its input reactance ( which is what
my program does.)

Then repeat the efficiency calculation and tell me what you get.
----
Reg.

Reg, According to NEC 4.1 the input impedance is near 40 ohms
(39.9373 + j 0.394926 ohms) at resonance (8.07 MHz). With
100 W input the total radiated power computes to 31.8 W. I am
continuing with checking the program to be certain I have not made
an error, and also working on a NEC solution to the input impedance
of one radial. Note that the computation also includes copper loss,
which should be insignificant. I have also included a copy of my
code below.

Frank

CM Reg's test Vertical
CE
GW 1 36 0 0 9 0 0 0.05
GC 0 0 .9 0.00082 0.00082
GW 38 3 0 0 0.05 0 0 -0.025 0.00082
GW 2 40 0 0 -0.025 0 10 -0.025
GC 0 0 1.11 0.00082 0.00082
GM 1 35 0 0 10 0 0 0 2 1 2 40
GE -1
GN 2 0 0 0 16 0.0067
FR 0 1 0 0 8.07 0.01
EX 0 38 2 00 89.37696044 0
LD 5 1 1 36 5.8001E7.......

........................

.........................
LD 5 36 1 60 5.8001E7
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN

Length & number of radials again
 

Frank,
Thanks for information so far. I need time to study it.

Could you tell me the

efficiency,
antenna input resistance component
and resonant frequency,

using our standard set of input data, ie., 36 radials, 10 metres long,
when frequency is set exactly to its 1/4-wave resonant value around
8.3 MHz. Input reactance = zero or very few ohms.

Thanks.
----
Reg.

Length & number of radials again
 

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 this:(the 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

Length & number of radials again
 

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 this:(the 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

Length & number of radials again
 

Frank,
Thanks for information so far. I need time to study it.

Could you tell me the

efficiency,
antenna input resistance component
and resonant frequency,

using our standard set of input data, ie., 36 radials, 10 metres long,
when frequency is set exactly to its 1/4-wave resonant value around
8.3 MHz. Input reactance = zero or very few ohms.

Reg'

With the above parameters; summarizing the data obtained so far:

Efficiency 31.8%;
Antenna input resistance component 36.21 - j 3.1, and;
The resonant frequency 8.07 MHz.

73,

Frank

Length & number of radials again
 

Frank,

Having used NEC4 to derive the input impedance of a single radial, it
is now in your hands to settle the discussion about attenuation along
radials and the distance at which a radial becomes ineffective. The
spectators are waiting!

We already have the input impedance of a single radial of length 10
metres at 7.0 MHz, with resistivity = 150 and permittivity = 16.

Using our standard set of data, I suggest you increase the SINGLE
radial length in increments of 3 metres until the input impedance Zin
stops changing and becomes relatively constant. That value of Zin
will be equal to Zo = Ro + jXo, the complex characteristic impedance
of the equivalent transmission line.

It might never become absolutely constant because NEC4 will take into
acount the effect of current flowing in the soil which, although it is
decreasing, eventually it will be substantially greater than that in a
long radial. ( My program does not do this.) But you should be able to
judge the distance at which radial attenuation is about 18 or 20dB,
ie., when Zin = Zo.

The question of efficiency is of less importance. It doesn't matter
what the efficiency is because you are using the antenna input
impedance plus radial input impedance only to deduce radial input
impedance in the same way as if you were measuring it. Be careful
with the signs of reactances. ;o)

At your leisure you may find a way how to do 36 and other numbers of
radials, at different frequencies. A 1/4-wave resonant antenna is
always best. The optimum length of a radial will decrease as
frequency increases. At 14 MHz the effect of permittivity kicks in
quite strongly. And with 120 or more radials you might be able to
demonstrate BL&E were quite correct when they concluded that a
virtually perfect ground. at MF, is independent of soil conditions.
----
Reg.

Length & number of radials again
 

Corrected numbers for linearly segemented radials from Frank's latest NEC-4
model of one buried radial wire, compared to Reg's program.

Side by side with the NEC-4 data


This is how many dB down the current is as you move outward from the origin
of the radial.

Distance Reg NEC-4 (dB down)

1.0 m 2.5 1.3

3.5 m 8.7 4.4

5.9 m 14.9 8.7

8.5 m 21.4 10.0

9.7 m 24.4 23.8

Conclusion: the current drop along the radial is no where near as fast as
Radials3 predicts, therefore shortening the radials as much as the program
shows will increase losses significantly.

I find it VERY interesting, that at the full length of 10m, there is good
agreement between Reg's program and NEC-4.

If I were going to base my conclusions on this preliminary small sample, I
would say that Reg's program does not hold up for short radials. BL&E, W8JI
and now NEC-4 all indicate that there is no where near 20 dB of attenuation
in short radials. To confirm this isn't an odd case, a lot more runs would
need to be done with varying lengths and radial numbers...but I have to say,
it ain't lookin' good for Radials3 in terms of fairly representing the
rapidity with which currents diminish on a radial wire over its length.

Bottom Line:

For the present, the articles in QST, ARRL Handbook, Low-Band DX'ing and
W8JI's findings are the ones I would follow. The first three are all the
same study and that formula is based on BL&E. The following data are from a
spreadsheet I used to calculate the optimum length and number of radials
based on the above sources. I put the BL&E data in the spreadsheet as a
reference. The numbers are how many dB down the field strength was for a
given number and length of radials.

Brn/Lw/Ep



# Rad 0.137 wl 0.274 wl 0.411 wl
2 -4.36 -4.36 -4.05
15 -2.40 -1.93 -1.65
30 -2.40 -1.44 -0.97
60 -2.00 -0.66 -0.42
113 -2.00 -0.51 0 (Ref)


Here are a few runs for 80 meters of various numbers and lengths of radials
that should be within a dB or so of optimum (BL&E).(Based on the references
noted above) 3.7 mhz, 1/4 wave vertical. The formula is based on tip
separation at the perimeter. Too much separation increases loss, too little
wastes wire. All based on wavelenthgs, of course. I believe the maximum tip
separation recommended was .015 wavelength.

Available Wire # of Radials Length of Radials
500' 25 19.7' (not within a dB, not
enough wire)
1000' 36 27.8' (not within a dB, not
enough wire)
1500' 44 34.0'
2000' 51 39.3'
3116' 63 49.0 (should be within 0.5 dB
of BL&E Optimum)

My final setup will be 46 radials 50' long. I have 26 right now. It looks
like for 50' long radials, I should really have 63 of them, otherwise, I
could have stayed at 51 radials only 39.3' long. All this says is that I'm
not making the "most" out of the available wire I had. (which makes sense,
given I've added radials over time, and didn't have a final plan).

At this point, it looks like when copper prices drop, I need to get another
850' of wire and put in 17 more radials and I will have met the criteria for
the formula. (Be within 0.5 dB of maximum field strength according to BL*E).

If anyone wants a copy of the Excel spreadsheet, just email me and I'll send
it to you as an attachment.
Only two variables should be entered: Total length of available wire and
Frequency in Mhz. Everything else is calcuated.( I did not protect any of
the fields, so if you enter data into a calculated field, you'll have to
reload your spreadsheet from a non-messed-up one...so save a virgin copy
somewhere until you protect the appropriate cells.)

73,

....hasan, N0AN

Length & number of radials again
 

Reg Edwards wrote:
Having used NEC4 to derive the input impedance of a single radial, it
is now in your hands to settle the discussion about attenuation along
radials and the distance at which a radial becomes ineffective. The
spectators are waiting!

Reg, how did you determine how much attenuation there is
in a radial because of the surrounding ground?
--
73, Cecil http://www.qsl.net/w5dxp

Length & number of radials again
 

Fellow Experimenters, Frank and Hasan.

I havn't the foggiest idea what you are doing with NEC4 but you should
be aware that, according to Radial_3, there are 3 resonant frequencies
with a single radial at lengths shorter than 10 metres and at a
frequency of 7 MHz.

The propagation velocity is very low. VF = 0.225

Funny unexpected things happen on multi-resonant lines especially when
Zo has a relatively large positive angle. Before you draw any
conclusions about deducing attenuation from your output data you
should take into account the line is -

1/4-wave resonant at 2.4 metres.
1/2-wave resonant at 4.8 metres.
3/4-wave resonant at 7.4 metres.

and at 10 metres it is very near to full-wave resonance. It can be
assumed the far end is open-circuit. Actually it isn't. It behaves
as if it is slightly longer.

It is significant that at 10 metres and 7 MHz, you have concluded that
the radial is about 20dB long. Which approximately agrees with my
program as being the length beyond which there is not much point in
extending it.

But the best way of determining attenuation is to do what I have
suggested - increase radial length in short increments and observe
what happens to radial input impedance. Eventually, Zin will converge
on Zo if it hasn't already done so. I should very much like to know
what Zo is and at what length it occurs. I have to assume NEC4 knows
what it's doing! ;o)
----
Reg.

Length & number of radials again
 

Reg, how did you determine how much attenuation there is
in a radial because of the surrounding ground?
--
73, Cecil
==========================================
Cec,

I don't have enough time left to write a thick book. But as an
engineer and radio amateur with 60 years (on and off) experience of
transmission lines ( from 0.05 Hz to 3 GHz ), and having once read
something about Oliver Heaviside's trouble with university professors,
I was able to make an intelligent guess.

It remains to be seen what the uncertainty is.

Isn't there anything in the Handbook or Google? ;o)
----
Yours, Reg.

Length & number of radials again
 

Fellow Experimenters, Frank and Hasan.

I havn't the foggiest idea what you are doing with NEC4 but you should
be aware that, according to Radial_3, there are 3 resonant frequencies
with a single radial at lengths shorter than 10 metres and at a
frequency of 7 MHz.

The propagation velocity is very low. VF = 0.225

Funny unexpected things happen on multi-resonant lines especially when
Zo has a relatively large positive angle. Before you draw any
conclusions about deducing attenuation from your output data you
should take into account the line is -

1/4-wave resonant at 2.4 metres.
1/2-wave resonant at 4.8 metres.
3/4-wave resonant at 7.4 metres.

and at 10 metres it is very near to full-wave resonance. It can be
assumed the far end is open-circuit. Actually it isn't. It behaves
as if it is slightly longer.

It is significant that at 10 metres and 7 MHz, you have concluded that
the radial is about 20dB long. Which approximately agrees with my
program as being the length beyond which there is not much point in
extending it.

But the best way of determining attenuation is to do what I have
suggested - increase radial length in short increments and observe
what happens to radial input impedance. Eventually, Zin will converge
on Zo if it hasn't already done so. I should very much like to know
what Zo is and at what length it occurs. I have to assume NEC4 knows
what it's doing! ;o)
----
Reg.

Reg, Note that I am making all my calculations at 8.07 MHz, where
the structure is very close to resonance. NEC does indicate
the resonant lengths of the radials as follows:

1/4 wave = 2 m;
1/2 wave = 4 m......etc., to 1.25 wavelengths at 10 m.

I will try your suggestion of gradually increasing radial length
until I see a convergence trend at the complex Zo.

Frank

Length & number of radials again
 

Frank's wrote:
Here's what the EZNEC manual says: "Horizontal wires should not
be placed exactly on the ground, but should be at least 1/1000
wavelength above (and in the case of EZNEC/4, also below) the
ground."

Cecil, Probably the 1/1000 WL limit contains a safety margin.
This does not appear to be addressed by either the NEC 2,
or NEC 4 user manual.

From the NEC-2 User's Guide, p. 11: ". . .for a horizontal wire with
radius a, and height h, to the wire axis, [h^2 + a^2]^1/2 should be
greater than about 10^-6 wavelenths. Furthermore, the height should be
at least several times the radius for the thin-wire approximation to be
valid." All I can find in the NEC-4 manual is the restriction in terms
of wire radius.

Cebik's book "Intermediate Antenna Modeling", p 1-12,
states: "The minimum height for wires above
a Sommerfeld-Norton ground has two dimensions. The first
relates the height above ground limit to the wire radius.
The wire height (h) should be several times the wire radius
(a), that is, h~a. As well, the minimum height is related to
the wavelength for the frequency in use:
(h^2 + a^2)^(1/2)10^(-6)Lambda. If a is very small
compared to h, the wires may approach 10^(-6) Lambda
toward ground. ......reflection Coefficient approximation....
... the general recommendation is that ......
horizontal wires should be () 0.4 Lambda above ground".

Obviously, from the manual quote, EZNEC can invoke a
Sommerfeld-Norton ground.

Yes. EZNEC's "Real, High-Accuracy" ground is the NEC Sommerfeld-Norton
ground.

. . .

Roy Lewallen, W7EL

Length & number of radials again
 

Frank,

After correcting the resonant lengths for the change in frequency from
7 to 8.07 MHz there is almost exact agreement between NEC4 and
Radial_3.

Keep a record of length, Rin, jXin for each incremental increase in
length. They could be useful.

When using Radial_3 set the number of radials to 1. The input
impedance of the radial system will then be same as the input to the
single radial and will be displayed with a greater number of
significant figures.

When you compare results between the two programs set the frequency on
Radial_3 also to 8.07 MHz. The resonant frequency of the Radial_3
antenna is slightly higher - it's something to do with the end-effect
and the fact that a vertical antenna needs pruning by a few percent to
make it resonate at the theoretical value of 75/Height MHz. Since at
present we are concerned only with the radials it is better to use the
same frequency for both programs.

I think that will complete all I have in mind. It may involve you
with a tedious amount of work. If you find it interesting you could
do something similar at 28 MHz. The 20dB limit may be reached with an
even shorter length of radial. Radial resonances ( which BL&E never
dreamed of ) will be much more pronounced especially with high ground
resistivity.

Has anybody ever generated an input table for 120 radials?

It's all in the cause of Science. Thanking you in advance.
----
Reg.

Length & number of radials again
 

Reg Edwards wrote:
Frank,

After correcting the resonant lengths for the change in frequency from
7 to 8.07 MHz there is almost exact agreement between NEC4 and
Radial_3.

Keep a record of length, Rin, jXin for each incremental increase in
length. They could be useful.

When using Radial_3 set the number of radials to 1. The input
impedance of the radial system will then be same as the input to the
single radial and will be displayed with a greater number of
significant figures.
(snip)

Does Radial_3 assume that each radial is independent of its neighbors,
regardless of how close or far?

Length & number of radials again
 

From the NEC-2 User's Guide, p. 11: ". . .for a horizontal wire with
radius a, and height h, to the wire axis, [h^2 + a^2]^1/2 should be
greater than about 10^-6 wavelenths. Furthermore, the height should be at
least several times the radius for the thin-wire approximation to be
valid." All I can find in the NEC-4 manual is the restriction in terms of
wire radius.

Cebik's book "Intermediate Antenna Modeling", p 1-12,
states: "The minimum height for wires above
a Sommerfeld-Norton ground has two dimensions. The first
relates the height above ground limit to the wire radius.
The wire height (h) should be several times the wire radius
(a), that is, h~a. As well, the minimum height is related to
the wavelength for the frequency in use:
(h^2 + a^2)^(1/2)10^(-6)Lambda. If a is very small
compared to h, the wires may approach 10^(-6) Lambda
toward ground. ......reflection Coefficient approximation....
... the general recommendation is that ......
horizontal wires should be () 0.4 Lambda above ground".

Obviously, from the manual quote, EZNEC can invoke a
Sommerfeld-Norton ground.

Yes. EZNEC's "Real, High-Accuracy" ground is the NEC Sommerfeld-Norton
ground.

. . .

Roy Lewallen, W7EL

Thanks Roy, To be honest I did not really check the NEC 2 manual,
just NEC 4, so understand why I could not find it. My NEC 2
manual is probably a different version -- WDBN version 0.92,
and it appears on page 13.

Regards,

Frank

Length & number of radials again
 

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

After correcting the resonant lengths for the change in frequency from
7 to 8.07 MHz there is almost exact agreement between NEC4 and
Radial_3.

Keep a record of length, Rin, jXin for each incremental increase in
length. They could be useful.

When using Radial_3 set the number of radials to 1. The input
impedance of the radial system will then be same as the input to the
single radial and will be displayed with a greater number of
significant figures.

When you compare results between the two programs set the frequency on
Radial_3 also to 8.07 MHz. The resonant frequency of the Radial_3
antenna is slightly higher - it's something to do with the end-effect
and the fact that a vertical antenna needs pruning by a few percent to
make it resonate at the theoretical value of 75/Height MHz. Since at
present we are concerned only with the radials it is better to use the
same frequency for both programs.

I think that will complete all I have in mind. It may involve you
with a tedious amount of work. If you find it interesting you could
do something similar at 28 MHz. The 20dB limit may be reached with an
even shorter length of radial. Radial resonances ( which BL&E never
dreamed of ) will be much more pronounced especially with high ground
resistivity.

Has anybody ever generated an input table for 120 radials?

It's all in the cause of Science. Thanking you in advance.
----
Reg.

I find this very interesting Reg, and learn more about NEC
all the time. I think I could probably do a 120 radial model;
particularly with segment length tapering. With linear
segmentation, and 0.025 m segment length, the 36 radial
model has almost 15,000 segments. It seems that
radial segments can be sloped to their final depth, so
can probably reduce the segmentation requirement.

Frank

Length & number of radials again
 

Reg Edwards wrote:

[snip]

. . . Radial resonances ( which BL&E never
dreamed of ) will be much more pronounced especially with high ground
resistivity.

Reg,

I have no idea what BL&E might have dreamed of, but I did find one
curious item on the fifth page of their paper (page 757 in the original).



Where there are radial ground wires present, the earth current consists
of two components, part of which flows in the earth itself and the
remainder of which flows in the buried wires. As the current flows in
toward the antenna, it is continually added to by more displacement
currents flowing into the earth. It is not necessarily true that the
earth currents will increase because of this additional displacement
current, since all the various components differ in phase.



Whether this is "resonance" I cannot say. However, it is pretty clear
they understood that the radial currents did not monotonically increase
as the distance from the antenna decreased. There was some sort of
variation.

Their figure 42 seems to show significant "resonance", but there does
not appear to be any discussion of that behavior.

73,
Gene
W4SZ

Length & number of radials again
 

"Gene Fuller" wrote

Whether this is "resonance" I cannot say. However, it is pretty
clear
they understood that the radial currents did not monotonically
increase
as the distance from the antenna decreased. There was some sort of
variation.

Their figure 42 seems to show significant "resonance", but there
does
not appear to be any discussion of that behavior.

==========================================
I find it easier to think in terms of ground currents flowing 'away'
from the focal point rather than coming into it.

At 3 MHz, where BL&E made their measurements, in ordinary soils there
are hardly enough resonant effects to be noticed. At MF and below
there are no resonant effects. The equivalent transmission line is
mainly resistive. There is inductance of the radial wire but
propagation is largely independent of the value of soil permittivity
and hence on 'capacitance'.

Resonance effects begin to show at 7 MHz, At 21 MHz permittivity and
inductance predominate - especially with high ground resistivities.

At higher frequencies in very high resistance soils, buried radials
take on the characteristics of the elevated variety. But nobody uses
buried radials with vertical antennas at 30 MHz and above. Everybody
switches to dipoles!
----
Reg.

Length & number of radials again
 

"John Popelish" wrote
Does Radial_3 assume that each radial is independent of its
neighbors,
regardless of how close or far?
=======================================

No John. The input impedance of a set of radials is not the sum of
the individuals all in parallel. Input impedance is a non-linear
function of N, the number of radials.
----
Reg.

Radiating Efficiency
 

Cecil, could you or somebody, please use Eznec or something, to
determine the radiating efficiency of a 9.0 meter long vertical
antenna with a ground-loss connection resistance of 5 ohms, at its
1/4-wave resonant frequency slightly above 8 MHz.

Will discuss the result later.

- and oblige Reg.

Radial attenuation
 

Cecil,

There has been a temporary improvement in my Alzeimer's affliction.

The attenuation along a radial is given by =

Attenuation = ( R / Ro + G * Ro ) / 2 nepers.

Where -

R = HF Conductor resistance.
G = Shunt leakance or conductance, related to soil conductivity.
Ro = Resistive component of line impedance Zo.

One neper = 8.686 dB.

If I published the source code you would be asking even more questions
and Richard Clark would again unjustly accuse me of trolling. ;o)
----
Reg.

Radiating Efficiency
 

Reg Edwards wrote:
Cecil, could you or somebody, please use Eznec or something, to
determine the radiating efficiency of a 9.0 meter long vertical
antenna with a ground-loss connection resistance of 5 ohms, at its
1/4-wave resonant frequency slightly above 8 MHz.

Is the 5 ohms of ground loss the only loss in the system?
i.e. should perfect ground be used? Or should it be done
in free space with a 5 ohm load going to the radials.

Will integrating the area of the omnidirectional elevation
envelope yield a value proportional to the radiated power?
--
73, Cecil http://www.qsl.net/w5dxp

Radiating Efficiency
 

Will integrating the area of the omnidirectional elevation
envelope yield a value proportional to the radiated power?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil, that is what I did with NEC, and got an efficiency
of about 35%. Using the ratio of Rr/(Rr+Rloss)
produces a totally different answer.

NEC 4 computes a normalized far field, at 1 m, in units
of volts. NEC 2 incorrectly shows units of V/m.

Frank

Radiating Efficiency
 

Frank's wrote:
Will integrating the area of the omnidirectional elevation
envelope yield a value proportional to the radiated power?

Cecil, that is what I did with NEC, and got an efficiency
of about 35%. Using the ratio of Rr/(Rr+Rloss)
produces a totally different answer.

NEC 4 computes a normalized far field, at 1 m, in units
of volts. NEC 2 incorrectly shows units of V/m.

W7EL tells us that EZNEC doesn't display the surface
wave which obviously contains power. Would that affect
the efficiency using the integration technique?
--
73, Cecil http://www.qsl.net/w5dxp

Radial attenuation
 

On Tue, 25 Jul 2006 12:22:38 +0100, "Reg Edwards"
wrote:

and Richard Clark would again unjustly accuse me of trolling. ;o)

Hi Reggie,

Do those nails in your palms really 'urt that much?

73's
Richard Clark, KB7QHC
(rolling dice at the bottom of Reggie's posts)

Radial attenuation
 

On Tue, 25 Jul 2006 12:22:38 +0100, "Reg Edwards"
wrote:

Cecil,

There has been a temporary improvement in my Alzeimer's affliction.

The attenuation along a radial is given by =

Attenuation = ( R / Ro + G * Ro ) / 2 nepers.

Where -

R = HF Conductor resistance.
G = Shunt leakance or conductance, related to soil conductivity.
Ro = Resistive component of line impedance Zo.

One neper = 8.686 dB.

If I published the source code you would be asking even more questions
and Richard Clark would again unjustly accuse me of trolling. ;o)
----
Reg.

Hi Reg,

I believe your temporary Alzhiemers affliction began some time ago, when you
repeatedly reminded me that BLE forgot to indicate the ground conditions. Even
though the conditions are irrelevant when sufficient radials effect a
near-perfect ground, you either skimmed BLE too quickly, or the Alzhiemers
effect had already taken place. I'm going to quote from two BLE pages below:

"Fig 7 earth conductivity = 0.2 x 10^-4 mhos/cm^3
Fig 8 earth conductivity = 1.0 x 10^-4 mhos/cm^3
Fig 9 earth conductivity = 0.2 x 10^-4 mhos/cm^3
Fig 10 earth conductivity =1.0 x 10^-4 mhos/cm^3"

"Fig 18 shows the distribution of earth loss for G = 22 degrees, and G = 88
degrees, for 15 and 113 radial wires, when the frequency was 3000 kilocycles and
the earth conductivity is 0.2 x 10^-4 mhos per cm^3."

It's true they didn't mention permittivity, but at least they did recognize
conductivity, and reported it.

On the other hand, concerning the difference in results between using BLE or
Radials3, unless I missed the critical point somewhere along the way, perhaps
the difference has been misunderstood, where Radials 3 shows usefulness drops
off more quickly with distance from the radiator than BLE. As I understand it,
when only a few radials are present, the longer length is unnecessary. I now
quote again from BLE:

"Fig. 6 shows the actual current in the earth for the same conditions. These
diagrams show that the ground system consisting of only 15 radial wires need not
be more than 0.1 wavelength long, while the system consisting of 113 radials is
still effective out to 0.5 wavelength."

Does this not agree with Reg's Radials3? If not, please tell me what I'm
missing. (I do not have Radials3, and am only commenting from what I've read in
the various posts.)

Walt, W2DU

Radial attenuation
 

"Walter Maxwell" wrote
... I now quote again from BLE:
"Fig. 6 shows the actual current in the earth for the same conditions.
These
diagrams show that the ground system consisting of only 15 radial wires
need not
be more than 0.1 wavelength long, while the system consisting of 113
radials is
still effective out to 0.5 wavelength."

Does this not agree with Reg's Radials3? If not, please tell me what I'm
missing. (I do not have Radials3, and am only commenting from what I've
read in
the various posts.)
___________

Possibly not. Here is a paste of one the early responses to the first
thread started by Reg on this subject , which shows that with radials_3,
radiation efficiency doesn't just stop improving with longer radials, it can
also get worse.

QUOTE

Reg, a bit confused by these results from RADIAL_3

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%

??

Dan

END QUOTE

/RF

Radial attenuation
 

On Tue, 25 Jul 2006 12:32:49 -0400, Walter Maxwell
wrote:

you either skimmed BLE too quickly, or the Alzhiemers
effect had already taken place.

Hi Walt,

Reggie's only defense against plagiarism (a charge he loves to bandy
about) is claiming to have NOT read BLE. It mimics his railing
against software users as intellectual cripples when he has a trove of
software offered like dope to school children on the playground.

Reggie,

It is amazing how you can spit in the faces of those commending you
for your software; and you do it with full vigor and glee. You may
want to ponder your legacy as a maker of crutches (un-referenced
executables) or leaving a testimony in open source code. Even with
these positive examples you sneer at your source to gain the
rhetorical advantage, and yes, that makes you a troll (and this is
decidedly different from what the Brit's call eccentrics, or what we
call characters).

The one complaint I've heard frequently from you when you are asked to
write something comprehensive (there are models in history from
Heavysides that you similarly dismiss) is that there is not enough
time. You seem to have plenty enough time to anticipate my banter, or
to otherwise respond to/with trivialities. This has got to be the
height of decadence.

73's
Richard Clark, KB7QHC

Radiating Efficiency
 

Cecil, that is what I did with NEC, and got an efficiency
of about 35%. Using the ratio of Rr/(Rr+Rloss)
produces a totally different answer.

NEC 4 computes a normalized far field, at 1 m, in units
of volts. NEC 2 incorrectly shows units of V/m.

W7EL tells us that EZNEC doesn't display the surface
wave which obviously contains power. Would that affect
the efficiency using the integration technique?
--
73, Cecil http://www.qsl.net/w5dxp

Good point Cecil, I forgot about the surface wave. Will have to
find a way of including it.

Frank

Radial attenuation
 

On Tue, 25 Jul 2006 11:11:28 -0700, Richard Clark wrote:

On Tue, 25 Jul 2006 12:32:49 -0400, Walter Maxwell
wrote:

you either skimmed BLE too quickly, or the Alzhiemers
effect had already taken place.

Hi Walt,

Reggie's only defense against plagiarism (a charge he loves to bandy
about) is claiming to have NOT read BLE. It mimics his railing
against software users as intellectual cripples when he has a trove of
software offered like dope to school children on the playground.

Reggie,

It is amazing how you can spit in the faces of those commending you
for your software; and you do it with full vigor and glee. You may
want to ponder your legacy as a maker of crutches (un-referenced
executables) or leaving a testimony in open source code. Even with
these positive examples you sneer at your source to gain the
rhetorical advantage, and yes, that makes you a troll (and this is
decidedly different from what the Brit's call eccentrics, or what we
call characters).

The one complaint I've heard frequently from you when you are asked to
write something comprehensive (there are models in history from
Heavysides that you similarly dismiss) is that there is not enough
time. You seem to have plenty enough time to anticipate my banter, or
to otherwise respond to/with trivialities. This has got to be the
height of decadence.

73's
Richard Clark, KB7QHC

Richard, what a masterful discourse on Reggie's character, oops, I mean
eccentricities!

Quite similarly, your earlier admonition to his lack of appreciation of BLE in
your stately defense of it as a document worthy of Lord Kelvin. Bravo!

Walt, W2DU