Dave wrote:
"David G. Nagel" wrote in message
...
John Smith wrote:
Richard Harrison wrote:
Art Unwin wrote:
"Could you give a similar description only this time make it a 5/8
wavelength antenna."
...
Best regards, Richard Harrison, KB5WZI
Richard:

I certainly don't want to engage in a large argument.

Rather, I would just venture an opinion directly related to my real world
construction experiences, and the results from the same:

If there are notable gains from constructing a 5/8 wave antenna, as
opposed to a 1/2 wave--I have NOT seen them.

It all looks good in EZNEC and/or mmana-gal (or, "on paper"), however, in
real world s-meter/signal-reports, "it" does not.

Perhaps I have experienced a anomaly(s?)

Or, put simply, the extra "hassle" in dealing with these extended lengths
is simply "not worth it!"

Regards,
JS
I think that we all should remember that it is the "ART" of antenna design
not the "SCIENCE" of antenna design.

Dave WD9BDZ

its only an art to art its a science to everyone else. art paints his
antennas with magical mystery jumping diamagnetic neutrinos that levitate in
the breeze. sounds like paintings like the melted watch and distorted
perceptions to me.


The last time that I built an antenna I used the formula to get the
appropriate length then I had to adjust it to obtain the optimal
readings for the frequency I was using.

Richard Harrison wrote:
Dave wrote:
"High power coaxial transmission lines have hollow center conductors."

Yes, and the metal which could have filled the hollow space would add no
conductivity at HF.

Best regards, Richard Harrison, KB5WZI


Ever seen the coax used on TV transmission lines? In rough numbers is is
a pipe about 6" in diameter with another pipe about 1" in diameter held
centered inside the larger one by spacers.

David G. Nagel wrote:

The last time that I built an antenna I used the formula to get the
appropriate length then I had to adjust it to obtain the optimal
readings for the frequency I was using.

Did "the formula" take into account any insulation, conductor resistivity,
conductor diameter, height above ground, characteristics of the ground,
and objects in the near field including supports?

If not, what is your point?


--
Jim Pennino

Remove .spam.sux to reply.

wrote:
David G. Nagel wrote:

The last time that I built an antenna I used the formula to get the
appropriate length then I had to adjust it to obtain the optimal
readings for the frequency I was using.

Did "the formula" take into account any insulation, conductor resistivity,
conductor diameter, height above ground, characteristics of the ground,
and objects in the near field including supports?

If not, what is your point?



The point is that those items are not part of "Antenna Theory: The
Science" but are a large part of "Antenna theory: The Art". Art has been
talking as if they are one and the same.

Something you could answer if you can. I am planning to install a dipole
antenna in NVIS configuration adjacent to a mobile home type structure.
The wire will be within about 10 to 15 feet of the metal covered
structure. How much will the metal warp the radiation pattern of the
antenna. It will be in the 75 to 60 meter bands.

Dave WD9BDZ

David G. Nagel wrote:
wrote:
David G. Nagel wrote:

The last time that I built an antenna I used the formula to get the
appropriate length then I had to adjust it to obtain the optimal
readings for the frequency I was using.

Did "the formula" take into account any insulation, conductor resistivity,
conductor diameter, height above ground, characteristics of the ground,
and objects in the near field including supports?

If not, what is your point?



The point is that those items are not part of "Antenna Theory: The
Science" but are a large part of "Antenna theory: The Art". Art has been
talking as if they are one and the same.

Science is fully accounting for all variables and their effects giving
you exact answers.

Art is experience and rules of thumb that get you close enough.


Something you could answer if you can. I am planning to install a dipole
antenna in NVIS configuration adjacent to a mobile home type structure.
The wire will be within about 10 to 15 feet of the metal covered
structure. How much will the metal warp the radiation pattern of the
antenna. It will be in the 75 to 60 meter bands.

Dave WD9BDZ

I can't but it should be easy enough to model in EZNEC.


--
Jim Pennino

Remove .spam.sux to reply.

On Nov 17, 3:49*pm, "David G. Nagel"
wrote:


Something you could answer if you can. I am planning to install a dipole
antenna in NVIS configuration adjacent to a mobile home type structure.
The wire will be within about 10 to 15 feet of the metal covered
structure. How much will the metal warp the radiation pattern of the
antenna. It will be in the 75 to 60 meter bands.

Dave WD9BDZ

I don't know about warping the pattern so much as making it possibly
hard to tune. You can expect some pretty serious coupling to all
that metal. So expect to have to prune it to a good match, and
maybe vary the exact tie off points of the dipole to move it a few
feet. Sometimes just a few feet can mean quite a bit of difference
in tuning.
As far as NVIS use, I wouldn't worry about the pattern too much.
It may skew it a bit, but I doubt it would really be much of a
problem.

wrote:
On Nov 17, 3:49 pm, "David G. Nagel"
wrote:

Something you could answer if you can. I am planning to install a dipole
antenna in NVIS configuration adjacent to a mobile home type structure.
The wire will be within about 10 to 15 feet of the metal covered
structure. How much will the metal warp the radiation pattern of the
antenna. It will be in the 75 to 60 meter bands.

Dave WD9BDZ

I don't know about warping the pattern so much as making it possibly
hard to tune. You can expect some pretty serious coupling to all
that metal. So expect to have to prune it to a good match, and
maybe vary the exact tie off points of the dipole to move it a few
feet. Sometimes just a few feet can mean quite a bit of difference
in tuning.
As far as NVIS use, I wouldn't worry about the pattern too much.
It may skew it a bit, but I doubt it would really be much of a
problem.



Thanks, your information is pretty much what I expected. The antenna
will be off the long side of the trailer and I didn't know if the NVIS
pattern would favor one direction or the other. I need a west favoring
direction.

Dave WD0BDZ

David G. Nagel wrote:
wrote:
David G. Nagel wrote:

The last time that I built an antenna I used the formula to get the
appropriate length then I had to adjust it to obtain the optimal
readings for the frequency I was using.

Did "the formula" take into account any insulation, conductor
resistivity,
conductor diameter, height above ground, characteristics of the ground,
and objects in the near field including supports?

If not, what is your point?


The point is that those items are not part of "Antenna Theory: The
Science" but are a large part of "Antenna theory: The Art". . .

I disagree. Antenna operation (or "theory") is dictated by science. How
the mentioned factors affect antenna performance can all be calculated
from well established, known scientific principles -- no "art" is required.

However, there are some ways where art does get into the picture.
Practical antenna design usually requires tradeoffs, and there isn't
necessarily one optimum solution. Weighing the tradeoffs, often
including cost and time, requires knowledge and skill, and is a creative
process that could properly be described as art -- although the more
science you know, the bigger the bag of tricks you'll have for your
"art" project. And there are often factors which, although completely
deterministic in principle, aren't well enough known or are too complex
to practically include in calculations. There, the skill or "art" comes
in having a sufficient knowledge of the likely effects of those factors
to choose or adjust the design accordingly.

What a lot of people call the "art" of antenna design is just a
substitute for understanding. If you don't understand the underlying
science or how to apply it, the only tool you have is Kentucky windage
and guesswork, often called "art" as opposed to real understanding.
While people can very often arrive at a usable solution by using nearly
all "art" and little "science", they have more and better solutions to
choose from as they replace some of that "art" with "science".

Roy Lewallen, W7EL

"David G. Nagel" wrote in message
...
Richard Harrison wrote:
Dave wrote:
"High power coaxial transmission lines have hollow center conductors."

Yes, and the metal which could have filled the hollow space would add no
conductivity at HF.

Best regards, Richard Harrison, KB5WZI


Ever seen the coax used on TV transmission lines? In rough numbers is is
a pipe about 6" in diameter with another pipe about 1" in diameter held
centered inside the larger one by spacers.

Yup. Also applies to rigid coax used for 400 MHz Naval radars.

In article tonline, Roy
Lewallen wrote:

I disagree. Antenna operation (or "theory") is dictated by science. How
the mentioned factors affect antenna performance can all be calculated
from well established, known scientific principles -- no "art" is required.


Hello, Roy and all. While I aggree with the above I think one has to keep
in mind that 50 years ago there weren't software MoM (e.g. NEC) and FDTD
tools around to implement calculations that don't lend themselves to
pencil-and-paper calculation. As a result back then there was
considerable "art" (I would call it engineering) involved in antenna
design. Hams, too, were coming up with many practical designs back then
as well as now. Practical experience was important then and still is.

However, there are some ways where art does get into the picture.
Practical antenna design usually requires tradeoffs, and there isn't
necessarily one optimum solution. Weighing the tradeoffs, often
including cost and time, requires knowledge and skill, and is a creative
process that could properly be described as art -- although the more
science you know, the bigger the bag of tricks you'll have for your
"art" project. And there are often factors which, although completely
deterministic in principle, aren't well enough known or are too complex
to practically include in calculations. There, the skill or "art" comes
in having a sufficient knowledge of the likely effects of those factors
to choose or adjust the design accordingly.

I think you've just summed up what engineering is all about. Mathematics
is an exact science; engineering is not.


What a lot of people call the "art" of antenna design is just a
substitute for understanding. If you don't understand the underlying
science or how to apply it, the only tool you have is Kentucky windage
and guesswork, often called "art" as opposed to real understanding.
While people can very often arrive at a usable solution by using nearly
all "art" and little "science", they have more and better solutions to
choose from as they replace some of that "art" with "science".

That's the difference between hobbyist tinkering and engineering. It's
what allowed the Wright Brothers to be successful when others (who may
have been close to success) failed. The Wrights took the time to
understand the science/physics, performed pertinent experiments and
meticulously collected and analyzed data. These endeavors set them apart
from their comtemporaries in pursuit of powered, heavier-than-air flight.
The Wrights were much more than bicycle mechanics; in their "off" time
they were (aeronautical) engineers. Sincerely,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337