"Lostgallifreyan" wrote in message me, and is the
one I need most to solve in my next efforts). What is this NEC program,
and
where can I find it? Sorry, but I have to ask, or Google will likely flood
me
with Nippon Electric Company details.

Start here for the explination. Near the bottom are some places to download
it. There are many versions and variations by slightly differant names.
Some free and some you have to buy.
http://en.wikipedia.org/wiki/Numeric...magnetics_Code





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On Sat, 11 Oct 2014 18:04:07 -0000, wrote:

Jeff Liebermann wrote:

snip

Speaking of dipole antennas, I did this study a while back:
http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html
Animated version:
http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html
It's a 1/2 wave dipole at various heights above a real ground. Any
semblance to textbook dipole pattern is long gone.

Yep, ground has a huge effect on some types of antennas.

An instructive slide show would be the vertical pattern of a horizontal
1/2 dipole at .1, .2, ... .5 wavelengths over ground.

Another one would be a 3 element beam at those heights.

I can do both of these, but I'm busy/lazy this weekend. I also can't
find the program I used to create the annimated GIF file. Argh. It
would also be helpful if someone would specify the frequency range of
interest.

I also did a study of monopoles of various lengths above a ground.
There are a few that are less than 1/4 wave long which should help
with some short antenna phenomenon.
http://802.11junk.com/jeffl/antennas/Monopole/index.html
Length Gain
wl dBi
0.050 4.75
0.125 4.85
0.250 5.19
0.500 6.96
0.625 8.01
Notice that the gain doesn't really drop very much when the monopole
is shorter than 1/4 wavelength long. A 1/2 wave dipole exhibits a
similar lack of gain loss for short antennas. So, why are short
antennas generally frowned upon? Lots of reasons but the big one are
losses in the matching networks. the 0.050 wavelength antenna looks
like about 700 ohms impedance. The 0.125 antenna is about

Nope, the vertical does the same thing when shortened from 1/4 as a
dipole shortened from 1/2 wave.

Thanks, that's what I meant to say but never finished the posting. I
had to run and clicked "send" before I was finished scribbling the
last paragraph.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 11 Oct 2014 21:49:11 -0000, wrote:

Jeff Liebermann wrote:
On Sat, 11 Oct 2014 11:47:22 -0500, John S
wrote:

Unless I have done something wrong, I see that a dipole that is .05
wavelengths long is within 20% of being as efficient as a half-wave
dipole. Even including wire resistance.

Sounds about right except that it doesn't include any losses
introduced by the necessary matching network and real ground losses at
HF frequencies. Expanding my table to include radiation efficiency:

There is no feed because it is the ANTENNA that is being analyzed, not
an antenna SYSTEM.

And while I don't know if the simulation included it, NEC can include
the ground losses for the ANTENNA.

I used a perfect ground for the monopoles. The NEC deck is shown
below the charts on each page. For example:
http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_050/slides/monopole_0_050.html
http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_125/slides/monopole_0_125.html
http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_250/slides/monopole_0_250.html
etc. Only the length of the monopole changes.

Ground and I^2R losses of the antenna are shown by NEC.
Matching losses are NOT part of the antenna.

Agreed. I used a perfect ground and ideal conductors in my very
simplistic models. The idea was to demonstrate that there is nothing
inherent in the length of the antenna that would have a major effect
on the gain. I threw in the other losses because I wanted to offer
reasons for why short antennas are not particularly popular. It's not
the antenna that's the problem. It's all the stuff that goes around
the antenna (matching loss, balun loss, combiner loss, tuner loses,
resistive losses, height above ground, counterpoise/ground losses,
mounting structures, feed line losses, feed line radiation, etc).

Yep, and once the issue of size versus efficieny is put to rest, it would
not be a bad idea to look at the real effects of ground, both in terms
of height in wavelengths and soil quality.

Yep. I threw those into the discussion without providing anything in
the model to demonstrate their effects. I could/should do that, but
I'm busy/lazy this weekend.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
On Sat, 11 Oct 2014 18:04:07 -0000, wrote:

Jeff Liebermann wrote:

snip

Speaking of dipole antennas, I did this study a while back:
http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html
Animated version:
http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html
It's a 1/2 wave dipole at various heights above a real ground. Any
semblance to textbook dipole pattern is long gone.

Yep, ground has a huge effect on some types of antennas.

An instructive slide show would be the vertical pattern of a horizontal
1/2 dipole at .1, .2, ... .5 wavelengths over ground.

Another one would be a 3 element beam at those heights.

I can do both of these, but I'm busy/lazy this weekend. I also can't
find the program I used to create the annimated GIF file. Argh. It
would also be helpful if someone would specify the frequency range of
interest.

It doesn't matter if everything is done in wavelengths.

I guess there are some who would want to see that a 160 meter dipole
at say .2 wavelengths high has the same pattern as a 2 meter dipole
at .2 wavelengths if for no other reason than to be assured the effects
are frequency independant.



--
Jim Pennino

On 10/11/2014 12:51 PM, wrote:
John S wrote:

snip

OK, so lets analyze my results:

Conditions are free space, wire is #14 gauge but may have zero ohms
where noted. The antenna is a dipole with the source connected at the
center, F=7MHz. I'm using EZNEC with a source of 1 watt. Antenna
resonance plays no part in this. # segments = 99 unless otherwise noted.

Lambda Wire Rin Gavg(dbi) Gmax(dbi) Efficiency

0.5 zero 80 0 2.16 100%
0.5 #14 73.6 -.09 2.08 98%

0.25 zero 13.2 0 1.85 100%
0.25 #14 13.7 -.17 1.69 96%

0.125 zero 3 0 1.78 100%
0.125 #14 3.25 -.33 1.45 93%

0.05 zero .464 0 1.76 100%
0.05 #14 .556 -.78 0.98 83%

Rin is the terminal resistance only. Gave is the average gain integrated
over the pattern, Gmax is the highest gain detected.

Unless I have done something wrong, I see that a dipole that is .05
wavelengths long is within 20% of being as efficient as a half-wave
dipole. Even including wire resistance.

I invite discussion in any case.

The diameter of #14 solid wire is 0.0641"; how about a line for #8, which
is 0.1285"?


0.05 #8 0.515 -.41 1.36 91.1%


Free space, no ground loss.

wrote in :

Look at this for an overview of NEC.

http://en.wikipedia.org/wiki/Numeric...magnetics_Code

At the bottom under External links you will find both free and commercial
implementations.

EZNEC by W7EL is popular among hams and has a free demo version that is
fully functional but limited in how complex a model you can generate.

NEC itself just crunches and produces numbers, but there are several
versions, including EZNEC, which have graphical interfaces to make
it easier to build the model and view the results.

I've used EZNEC+ for years.



Thanks again, I'll use that if it runs on W98. (Long story, but I decided to
stay with it for too many reasons not to do so). Graphic representations will
help me a lot. (There is a tool for laser beam optics that used graphical
feedback of inputs to demonstrate predictions, if it's anything like that one
it will be indispensible).

"Ralph Mowery" wrote in
:


"Lostgallifreyan" wrote in message me, and is the
one I need most to solve in my next efforts). What is this NEC program,
and
where can I find it? Sorry, but I have to ask, or Google will likely
flood me
with Nippon Electric Company details.

Start here for the explination. Near the bottom are some places to
download it. There are many versions and variations by slightly
differant names. Some free and some you have to buy.
http://en.wikipedia.org/wiki/Numeric...magnetics_Code


Thankyou. Fortunately this looks like it will be easier than finding certain
versions of the CGG compiler...

On 10/12/2014 6:54 AM, Lostgallifreyan wrote:
"Ralph Mowery" wrote in
:


"Lostgallifreyan" wrote in message me, and is the
one I need most to solve in my next efforts). What is this NEC program,
and
where can I find it? Sorry, but I have to ask, or Google will likely
flood me
with Nippon Electric Company details.

Start here for the explination. Near the bottom are some places to
download it. There are many versions and variations by slightly
differant names. Some free and some you have to buy.
http://en.wikipedia.org/wiki/Numeric...magnetics_Code


Thankyou. Fortunately this looks like it will be easier than finding certain
versions of the CGG compiler...


Also try EZNEC. They both use the NEC engine but EZNEC provides a
different interface to the modeling.

http://eznec.com/

John S wrote in :

Also try EZNEC. They both use the NEC engine but EZNEC provides a
different interface to the modeling.


Already did. EXNEC v5 demo. I really like the first impression I get, Runs
on all Win32 (very respectable), and I like the way I can grab the 3D plot
and rotate it like a SketchUp image to get a proper look at it. I mentioned a
laser beam tool (called PSST) that graphically models laser cavities, hoping
this EXNEC might be an antenna maker's equivalent. It is. It will take me
a while to understand it though.

On 10/12/2014 7:38 AM, Lostgallifreyan wrote:
John S wrote in :

Also try EZNEC. They both use the NEC engine but EZNEC provides a
different interface to the modeling.


Already did. EXNEC v5 demo. I really like the first impression I get, Runs
on all Win32 (very respectable), and I like the way I can grab the 3D plot
and rotate it like a SketchUp image to get a proper look at it. I mentioned a
laser beam tool (called PSST) that graphically models laser cavities, hoping
this EXNEC might be an antenna maker's equivalent. It is. It will take me
a while to understand it though.


These are complex applications which someone with a mindset not like
yours has produced. There will be a learning curve. The important thing
is to not get frustrated and give up. If you need help, ask.

Cheers.