On 10/5/2015 10:55 AM, rickman wrote:
On 10/5/2015 6:51 AM, John S wrote:
On 10/4/2015 11:29 AM, rickman wrote:
On 10/4/2015 10:05 AM, John S wrote:
How less efficient is a short vertical than a 1/4 vertical?

You are starting to sound like someone else.


Sorry guys. I didn't mean to sound like someone else. I regret starting
this post now. Let's just forget it.

I was just joking...


Well, okay.

I like to discuss these things in a gentlemanly manner and learn from
them. I like to use EZNEC and a Smith chart to support my thoughts,
opinions, findings, confusions, etc. My purpose is purely technical.

I like other peoples' input because, without it, there is no
constructive thinking about how to approach the problem. Your approach
may be different from mine because your brain and background is
different from mine. That is a good thing. If I can just view it your
way, and you can view it my way, we might gain a new insight into the
problem.

There are several contributors here whose posts I respect and value very
much. I know I can learn a lot here if only we can exclude the
protagonist and his followers by ignoring the British posts.

Summary: I already know that there are people here who can help me
reconcile my questions and investigations regarding technical aspects of
antennas, transmission lines, ATUs, and all the fodder we hams eat up.
Where else can I go to get this?

On Mon, 5 Oct 2015 12:41:18 -0500, John S wrote:

Summary: I already know that there are people here who can help me
reconcile my questions and investigations regarding technical aspects of
antennas, transmission lines, ATUs, and all the fodder we hams eat up.
Where else can I go to get this?

https://www.reddit.com/r/amateurradio/
http://www.eham.net/ehamforum/smf/
http://lists.contesting.com/pipermail/towertalk/
http://lists.contesting.com/archives//html/Towertalk/
etc...


--
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 Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

How less efficient is a short vertical than a 1/4 vertical?

Are you talking about radiation efficiency or total efficiency? Are
you including the losses in the matching system (loading coil or
antenna tuna losses) needed to match a shortened antenna?
http://www.antennex.com/w4rnl/col0504/amod75.html
http://www.antenna-theory.com/basics/gain.php

I would like to see some numbers.

http://802.11junk.com/jeffl/antennas/Monopole/index.html
This is a study of what various monopoles, over a perfect ground, look
like in terms of gain, impedance, efficiency etc. I should probably
make a summary table, but I'm busy today.

Note that the shortest antenna (0.050 wavelengths) still has 100%
efficiency:
http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_050/slides/monopole_0_050.html
That's because there are no dissipative components anywhere in the
antenna system. If you shove 100 watts of RF into this ideal antenna,
it will either radiate or reflect 100 watts, with no losses anywhere.
Well, an antenna with a 6594:1 VSWR isn't terribly useful, but if you
could find a suitable ideal matching network, it would work as well as
the ideal 1/4 wave monopole. Notice that I said "ideal" as in a loss
less matching network. That's not going to happen. The reason short
monopoles are a problem (such as an HF antenna on a vehicle) is that
the matching losses are ummm... lossy. As the antenna becomes longer,
the mismatch is less, the matching network less critical, and the
overall losses are less.

If you look again at the various results, you'll notice that the
shorter antennas have far more current going through them than the
longer antennas. If there are resistances in the elements (such as in
a loop antenna), the higher currents will result in higher losses for
shortened antennas. This may be a consideration for your less
efficient shortened vertical.

It is a ground plane with 4 radials
(typical). Free space.

Assume a source at the base. The type of source is your choice. EZNEC
defaults to one amp, but can be changed to a constant power of your choice.

I'm sure I've left out additional requirements, but maybe this will be
a healthy discussion even so. Suggestions are welcome.

Well, I do have a suggestion. Monopole antennas are very sensitive to
changes in the counterpoise, earth ground characteristics, number of
radials, elevation, etc. There is no univesal monopole model that
works for all frequencis, all conditions, and all applications.
Usefulness of the antenna also depends on the radiation angle and
ability to be matched to 50 ohms. I don't think a discussion that
bounces around all these parameters is going to be very useful.
Perhaps if you could provide a more specific set of conditions, we
might be able to analyze the situation in realistic terms, and
possibly provide recommendations and alternatives.

--
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 Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.


--
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 Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.

What do you mean you can't have a ground plane in free space?

There are no ground losses in free space, but ground plane antennas, i.e.
a radiator with radials, work just fine.



--
Jim Pennino

On Sun, 4 Oct 2015 18:56:18 -0000, wrote:

Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.

What do you mean you can't have a ground plane in free space?

There are no ground losses in free space, but ground plane antennas, i.e.
a radiator with radials, work just fine.

I'll stand my ground and defend my assertions on good grounds. Permit
me to explain from the ground up.

If you mount a monopole on the ISS, the NEC model would probably use
the space station surface as a ground. That's not exactly what I
would call "free space" because it costs so much to get into space,
but that doesn't enter into the calculations. The space station would
form a suitable ground plane where its presence in outer space is an
incidental coincidence. However, that's not the same as an "earth
ground", which is what I mean by a "real ground". Also, If I fire up
4NEC2, and setup the antenna in free space, the various grounding
options become grayed out. That would suggest that there ain't no
such thing as a ground or "earth ground" in expensive, errr... free
outer space.

Of course, I could design what is commonly called a "ground plane
antenna", which would rhetorically have a "ground plane". However,
that's not the same as an "earth ground". For example, if you
actually model a "ground plane antenna" over an earth ground, you
might end up with two grounds, which make little sense. Also,
adjusting the height above ground in a "ground plane antenna" make
equally little sense. The radials that form a "ground plane" should
be renamed to something more definitive, such as a conical
counterpoise or conical grounded sleeve antenna.

Ummm... how do I model coffee grounds or has this discussion ground to
a halt?


--
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 Sun, 4 Oct 2015 18:56:18 -0000, wrote:

Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.

What do you mean you can't have a ground plane in free space?

There are no ground losses in free space, but ground plane antennas, i.e.
a radiator with radials, work just fine.

I'll stand my ground and defend my assertions on good grounds. Permit
me to explain from the ground up.

If you mount a monopole on the ISS, the NEC model would probably use
the space station surface as a ground. That's not exactly what I
would call "free space" because it costs so much to get into space,
but that doesn't enter into the calculations. The space station would
form a suitable ground plane where its presence in outer space is an
incidental coincidence. However, that's not the same as an "earth
ground", which is what I mean by a "real ground". Also, If I fire up
4NEC2, and setup the antenna in free space, the various grounding
options become grayed out. That would suggest that there ain't no
such thing as a ground or "earth ground" in expensive, errr... free
outer space.

Of course, I could design what is commonly called a "ground plane
antenna", which would rhetorically have a "ground plane". However,
that's not the same as an "earth ground". For example, if you
actually model a "ground plane antenna" over an earth ground, you
might end up with two grounds, which make little sense. Also,
adjusting the height above ground in a "ground plane antenna" make
equally little sense. The radials that form a "ground plane" should
be renamed to something more definitive, such as a conical
counterpoise or conical grounded sleeve antenna.

Don't know about 4NEC2, but EZNEC has no problem with a ground plane
antenna in free space.

The ground plane in a ground plane antenna usually refers to the radial
elements attached to the bottom end of the radiator, so I don't see
any problem with such a configuration.

Now whether or not a ground plane antenna is a usefull design to use in
space is a separate issue.

But what is interesting is to model a ground plane over real ground
and step the height above real ground and observe what happens to the
pattern as the height goes from zero to a couple of wave lengths.

While getting a 40M ground plane up a half wave length would be a
challenge, at 12M and above it is not, and at 6M, most ARE mounted
at about 1 wavelength.

Ummm... how do I model coffee grounds or has this discussion ground to
a halt?

Depends on whether or not I have intrigued you enough to grind the
numbers for a ground plane at various heights.


--
Jim Pennino

On 10/4/2015 1:36 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.

Why not? Is not the ground just the other terminal on the antenna
connected to the radials? Ground doesn't have to be earth ground or
anything else. It is just a defined reference point.

--

Rick

On Sun, 4 Oct 2015 15:24:39 -0400, rickman wrote:

On 10/4/2015 1:36 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.

Why not?

Because a free space model is defined as the absence of a "real
ground", "earth ground", or something sufficiently away from the rock
that you're standing on so that its influence is very small on the
model. That's usually measured in wavelengths. Offhand, anything at
least 10 wavelengths above the nearest ground structure (ground,
trees, buildings, etc) can be ignored. For VHF/UHF, that's a fairly
small distance. For HF, much longer.

Is not the ground just the other terminal on the antenna
connected to the radials?

Nope. Which radials? The radials in a common "ground plane" antenna
are certainly not considered an "earth ground". However, the buried
counterpoise that forms the other half of a monopole antenna is
certainly an earth ground. Note that I would need an NEC4 runtime to
model a below ground radial counterpoise system.

Ground doesn't have to be earth ground or
anything else. It is just a defined reference point.

I think the problem is too many definitions of ground here. In my
world, "earth ground" means just that. It's the rock you're standing
on. A "grounded" antenna, is one that uses the earth as the
counterpoise. A "safety or lightning ground" is a path for
atmospheric electricity and does not usually enter in the
calculations.

Maybe some examples might help.

1. I want to model a UHF (440 MHz) vertical "ground plane" antenna
mounted on a pole on my roof. The roof is 20ft high and the antenna
is mounted on top of a 10ft pole. How high above "ground" do I make
my antenna model?

2. Same antenna, but with a #12 solid ground wire running to a ground
rod pounded into the ground. How high above "ground" do I make my
antenna model?

3. Assuming the pole is made from fiberglass, and RF power amp is
mounted at the antenna (common for cellular TMA installs), will a free
space model work?

4. If the 10ft pole it transplanted to the ISS, is there an "earth
ground" and how high?

Scroll down for my answers.














Looks like I'll be busy for a few days, so I might as well answer my
own questions now:

1. 10 ft. At UHF, the house is considered part of the earth ground
especially if the roof is corrugated steel or full of chicken wire.
Same with any LARGE mounting structure (in terms of wavelengths).

2. 10 ft. The ground wire is presumably not part of the radiating
parts of the antenna and can be ignored if shielded by the ground
plane wires. If long enough, it looks more like an RF choke
(inductor) than an antenna element.

3. Yes, free space will work, although nearby metal structures and
wires need to be considered if they can be "seen" by the radiating
elements.

4. Toss a coin and 10 ft. The ISS is large enough (in terms of
wavelengths at UHF) to be considered a perfect ground, as in my
monopole examples. However, if you need an accurate model, the ISS
has enough complex shapes that can re-radiate RF, and should probably
be modeled as part of the antenna system, in free space and without
any influence from the planetary rock.



--
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:

Maybe some examples might help.

1. I want to model a UHF (440 MHz) vertical "ground plane" antenna
mounted on a pole on my roof. The roof is 20ft high and the antenna
is mounted on top of a 10ft pole. How high above "ground" do I make
my antenna model?

About 30 feet, i.e. the height of the radials.

2. Same antenna, but with a #12 solid ground wire running to a ground
rod pounded into the ground. How high above "ground" do I make my
antenna model?

For the same antenna, the same height.

3. Assuming the pole is made from fiberglass, and RF power amp is
mounted at the antenna (common for cellular TMA installs), will a free
space model work?

Depends on the actual height above the ground in wave lengths and what
else is around.

4. If the 10ft pole it transplanted to the ISS, is there an "earth
ground" and how high?

The ground would be free space, but for accuracy you would need to
model the ISS.

Scroll down for my answers.









Looks like I'll be busy for a few days, so I might as well answer my
own questions now:

1. 10 ft. At UHF, the house is considered part of the earth ground
especially if the roof is corrugated steel or full of chicken wire.
Same with any LARGE mounting structure (in terms of wavelengths).

My roof is all non-conductive so I can ignore it. Your milage may
vary.

2. 10 ft. The ground wire is presumably not part of the radiating
parts of the antenna and can be ignored if shielded by the ground
plane wires. If long enough, it looks more like an RF choke
(inductor) than an antenna element.

Having actually modeled such, I can say that such a wire will have
little to no effect on the antenna unless it happens to be about
1/4 wavelength long.

3. Yes, free space will work, although nearby metal structures and
wires need to be considered if they can be "seen" by the radiating
elements.

We agree totally on this one.

4. Toss a coin and 10 ft. The ISS is large enough (in terms of
wavelengths at UHF) to be considered a perfect ground, as in my
monopole examples. However, if you need an accurate model, the ISS
has enough complex shapes that can re-radiate RF, and should probably
be modeled as part of the antenna system, in free space and without
any influence from the planetary rock.

I would think that the shape of the ISS is such that you would need
to model it and take into concideration the location relative to the
solar panels and their orientation.



--
Jim Pennino