On 10/12/2014 12:41 AM, wrote:
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.

Something else might be interesting; include the effects of sag
(centenary) in a wire antenna. Has anyone done that? I mean, using EZNEC
or NEC modeling.

On 10/12/2014 10:20 AM, John S wrote:
On 10/12/2014 12:41 AM, wrote:
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.

Something else might be interesting; include the effects of sag
(centenary) in a wire antenna. Has anyone done that? I mean, using EZNEC
or NEC modeling.


Arrgh! Catenary instead of what I posted. Damn spell checker is dumb on
a lot of math and engineering terms. Sorry

John S wrote in :

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.


Understood. Thanks. bear in mind that my mindset did manage to get to grips
with phase modulation synthesis, large scale polyphony and multitimbrality,
and accurate similautions of a few musical instruments, and did do alone with
nothing but expired patents and service manuals, and a very few other
published notes to guide me. I'm not trying to show off, my point is that
while I do not give up easily, I AM alone, so my time is divided. If after
my current break from that I go back to it, I might be listening to radio on
an antenna or two while not thinking of the antennas for months. I've always
been interested in this though, so I won't let it go. I'll look into NEC
because the whole thing about good grounds is a particular fascination now,
especially if improvising in limited or very temporary circumstances.

John S wrote in :

Something else might be interesting; include the effects of sag
(centenary) in a wire antenna.

Agreed. I was thinking about that possibility last night. Meaning 'catenary',
perhaps? As in 'hanging chain'? I doubt any longwire would lack this, so
modelling it would be useful.

John S wrote in :

Catenary instead of what I posted.

Yes. I should have read your second post before my first reply..

On Sun, 12 Oct 2014 05:41:37 -0000, wrote:

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.

That's why I ran the numbers at the traditional 1 meter (299.8MHz)
wavelength. Everything can be easily scaled by frequency.

The basic idea was to minimize the number of potential variables and
effects. I was only interested in the effects caused by the length
and/or height of the monopole, and didn't want to get into anything
that was frequency or material dependent. I think I've successfully
demonstrated that short dipoles have almost the same gain as a proper
1/2 wave dipole, if one only looks at the antenna, and ignores
literally everything else.

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.

As long as the frequency, matching, coax cables, skin depths, ground
characteristics, mounting structures, etc are the same, they'll be
identical. However, when frequency, site, and construction specifics
are included, such as the operating frequency, the height in meters
instead of wavelength, or the use junk wire are included, the model is
no longer frequency independent.

Somewhere on my computah is a series of models that I built for a
simple 20 meter dipole, that started with an idealized free space
model, and progressed towards a real installation which by coincidence
resembles my house. I threw in everything that might have an effect
on the pattern to see what might happen. I got stuck at including the
sloping hillside because NEC2 seems to only include a flat earth. I've
also done similar studies for commercial antennas mounted on very real
and quite cluttered towers. Doing these incrementally is an excellent
introduction into the difference between ideal antenna patterns, as
found in the literature, and the nightmarish reality of real antenna
installations.


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

wrote in message ...

Lostgallifreyan wrote:
wrote in :

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.


Thankyou. This is the bit I am most weak on (though I did not grasp all
the
previous detail, the ground loss was an issue not lost on 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.

# 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.

Me too. It has been extremely useful in identifying promising approaches
without having to build the hardware for each.

On 10/12/2014 11:14 AM, Lostgallifreyan wrote:
John S wrote in :

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.


Understood. Thanks. bear in mind that my mindset did manage to get to grips
with phase modulation synthesis, large scale polyphony and multitimbrality,
and accurate similautions of a few musical instruments, and did do alone with
nothing but expired patents and service manuals, and a very few other
published notes to guide me. I'm not trying to show off, my point is that
while I do not give up easily, I AM alone, so my time is divided. If after
my current break from that I go back to it, I might be listening to radio on
an antenna or two while not thinking of the antennas for months. I've always
been interested in this though, so I won't let it go. I'll look into NEC
because the whole thing about good grounds is a particular fascination now,
especially if improvising in limited or very temporary circumstances.


Excellent! I like to explore and I encourage everyone to do so whether
it be with math tools or getting your hands dirty. Keep it up.

Cheers.

On 10/12/2014 11:19 AM, Lostgallifreyan wrote:
John S wrote in :

Catenary instead of what I posted.

Yes. I should have read your second post before my first reply..

No problem. Your reply was completely appropriate. We might be just a
bit out of sink (he, he) sync. Let's not get too serious.

John S wrote in :

Excellent! I like to explore and I encourage everyone to do so whether
it be with math tools or getting your hands dirty. Keep it up.


Indeed. That synth I mentioned, it took me a good chunk of lifetime
waiting for someone to make so I could pay for it. I gave up waiting.

Jeff just posted about the perils of antenna towers and hillsides vs NEC2's
flat earth, and many earlier things (liek modellign with Sketchup prior to
engineering in metals and plastics, have taught me caution. measure thrice,
cut once. THis is how and why I want to use NEC, to save me from falling into
expensive and time consuming traps, which I think it will do very well.