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

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

BTW, love your programs... tried this one out because I've bought 4
kilofeet of 18 gauge wire for a vertical antenna when I get a backyard
in a couple of weeks.
73,
Dan

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
========================================
Dan,

The up-and-down change in efficiency versus radial length is due to
resonance effects. With a high value of soil resistivity of 500
ohm-meters resonance is not completely damped down. This is also
indicated by the relatively small decibels per 1/4-wavelength figure.

As radial length is varied the input resistance of the 96 radials
changes. Look at the wavelength of 1 wire figure. It will be seen
that length passes through 0.5 wavelength resonance at 6.0 metres. It
passes through 1.0 wavelength resonance at 11.6 metres. At both these
lengths the input resistance is at a maximum and so efficiency is at a
minimum.

At 2.9 metres and 8.8 metres the radials are in 1/4-wave and 3/4-wave
resonant and the input resistance is at a minimum and
efficiency is at a maximum.

Vary length while watching the resistive component of input impedance
to see what happens. It's highlighted in red.

If you reduce soil resistivity from 500 to 50 ohm metres the resonance
effects will probably disappear and the decibels per quarter
wavelength will increase. All resonant effects will have disappeared
when radial attenuation is about 18 or 20dB or greater.

The effects of resonance are not observed so well when frequency is
varied because so many other things change as frequency is varied over
an octave or more.

Resonant effects are much greater at 20 MHz and above with very high
resistance soils such as desert sand. The radials then behave very
similarly to the elevated variety.

I trust your confusion has now gone away. ;o)
----
Reg, G4FGQ

"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

"Reg Edwards" wrote in
:

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.

Very nice. But one thing I have noticed is that radial effectiveness
begins to fall off at a distance from the antenna very similar to its
height. This seems to be due to capacitive coupling between the top of
the antenna and the radials. Does your algorithm take this effect into
consideration?

I modelled an antenna I used to use and the results did seem consistent
with the behaviour, though. Actually I used to use two of them, and
actually had a gain over a single perfect-ground antenna. Not a LARGE
gain, but still, useful. More useful was the fact that I could control
the take-off angle and pattern to the point where the antenna actually
sounded about 10db louder than a low dipole--at distances of 1000 mi or
more.


--
Dave Oldridge+
ICQ 1800667

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

I don't know about boundary conditions, but when I use this program to
evaluate the following system:

3.62 Mhz, 18.3 meter height (simulating an inverted L with 25.4 ohms Rrad)

Resistivity 25, Permittivity 25

2mm radials, 4mm antenna wire, radials 1 mm depth (actually #14 insulated
wire, stapled to the lawn and sinking in gradually)

...it shows my predicted efficiency with (26) 50' long radials to be about
90%.

My measurements indicated I am getting about 88%. Pretty good agreement.

What causes me to cringe, is that the program shows that I can reduce the
length of my radials from 16.1 meters to a little over 4 meters without
losing ANY significant efficiency. Given everything else I've read over the
years, that just seems to be way too good to be true.

Now, I suppose I could rip up my 26 radials and shorten them all to about 5
meters and re-measure my efficiency, but that's a LOT of work (and it's 97
degrees out with a dew point in the mid 70's). Not going to happen.

Here's the kicker... I have 1000' of remaining wire to put down (and I am
going to add it). If this value of 4 or 5 meters (15 feet, let's say) is
even remotely correct, I can put down 66 more radials (although they would
be interlaced with the existing 26 longer ones of 50' each).

Using my initial length of 50', I can put down 20 more radials, giving me a
total of 46 radials 50' long.

Reg, you program seems to be telling me that I would get the maximum benefit
by putting in 66 more radials approximately 15' long, and that installing
them at 50' would be wasting 35' of wire per radial, and reducing radial
coverage as well.

So...what should I do:

1. Add 66 greatly shortened radials (accepting Reg's program as correct)

or

2. Add 20 radials, maintaining my 50' length that I originally used.

I look forward to comments.

....hasan, N0AN

On Wed, 19 Jul 2006 11:48:47 -0500, "hasan schiers"
wrote:

So...what should I do:
2. Add 20 radials, maintaining my 50' length that I originally used.

Hi Hasan,

Build for the future. Anticipate working 160M. Enjoy the advantages
(as slim as they may be) at 80M.

73's
Richard Clark, KB7QHC

Good thinking, Richard, as I may try to get this inverted L to do 160 in the
fall/winter by adding a trap to the 80m inverted L and extending the wire
for 160m resonance.

Incidentally, over the weekend I tried to add a 40m wire parallel to the 80m
L...it was a complete failure. (I used a "fan" approach with 6" standoffs
for the 33' vertical wire). I thought I might get 2 fer 1 at the feedpoint,
but it just didn't work worth a darn. Very low noise level, signals were
significantly weaker than my Carolina Windom 80 (on 40m) up 42'. I did work
a few DX stations with it, but just not up to my expectations. A properly
performing 40m 1/4 w vertical over very good soil and a full radial field as
described in my prior message should have been outstanding. It wasn't. It
was very hard to tune, showed no better than a 3:1 VSWR at resonance, and
was only marginally better on a very few signals between sunset and sunrise.
Very disappointing.

So...your suggestion for 160m is a good one. I could do a trap pretty
easily. If I wanted to try 40m with the same feedpoint, I could put a
parallel tuned circuit at the feedpoint and run the 80m inverted L as a 40m
half-wave. Of course, this requires switching at the feedpoint and I'm not
sure I'd bother. I also have to get a 1.9 uH coil and 250 pf variable cap to
do the tuned circuit (per ON4UN's Low Band DXing Handbook). I found an
acceptable cap for 40 bucks and coil stock is readily available. I just have
to get motivated and work out the relay switching.

I wondered if I could EVALUATE the effectiveness of the 80m inverted L on
40m as a half wave, by temporarily taking an antenna tuner with wide range
(T-network matches almost anything) out to the feedpoint and matching it
there. If it hears well, and works ok at 300w (tuner limit), then it might
be worth investing in the coil/cap/relays to switch a more standard high-Z
feed in and out. What do you think?

Thanks for your input.

73,
....hasan, N0AN
"Richard Clark" wrote in message
...
On Wed, 19 Jul 2006 11:48:47 -0500, "hasan schiers"
wrote:

So...what should I do:
2. Add 20 radials, maintaining my 50' length that I originally used.

Hi Hasan,

Build for the future. Anticipate working 160M. Enjoy the advantages
(as slim as they may be) at 80M.

73's
Richard Clark, KB7QHC