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

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

hasan schiers wrote:

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?

The configuration of 35ft vertical + 35ft (or so) horizontal worked well
for me on 40m at the old QTH, and was quite effective on 80m DX. For
160m, I added a 100ft loading wire to bring the total length up to about
130ft, and that configuration doubled as an end-fed half-wave for 80m
short-skip.

Having a QRO auto-ATU made band changing easy, so it wasn't necessary to
resonate the antenna on any band. However, the quarter-wave resonances
on 80m and 160m could have been trimmed to length.

Coming back to the difference between the 40m vertical quarter-wave and
the bent half-wave, I compared the bare 35ft mast and the same mast with
the added loading wire and didn't find much difference. For DX, the
bent-half-wave should have been down on the quarter-wave (because some
of the radiation was being wasted at high angles); but in contests, both
antennas seemed to work the same regular DX stations. The bent half-wave
was louder for short-skip, which meant more QRM at night, but made it
easier to continue making low-point contacts during daylight hours.

If you use an 80m trap, the antenna could still work on 40m but the
horizontal section would be way over-long. Unless rapid band changing
between 80m and 160m is a priority, I'd suggest you use a physical
disconnect at the end of the 35ft horizontal section. (My setup made it
very easy to loosen a rope and lower the connection into reach, so I
used simple banana plugs, with snap links to add either wire or plain
cord.)




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

On Wed, 19 Jul 2006 13:03:16 -0500, "hasan schiers"
wrote:
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.

Hi Hasan,

I must think that you were only slightly off in length, and that the
proximity, even at 6 inches, is still proximal.

Very low noise level, signals were
significantly weaker than my Carolina Windom 80 (on 40m) up 42'.

Not unlike many similar reports.

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.

Some of those same reporters suggest split operation where the
vertical is the radiator and a high horizontal is the receiving
antenna.

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?

I would encourage that, simply because you seem to be amenable to such
a path already. Gaining experience is always a noble work.

73's
Richard Clark, KB7QHC

"hasan schiers" wrote in message
...
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.

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

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