Reg Edwards wrote:
I answered your original question by saying that the near field due to a
halfwavelength of wire along an antenna with standing waves (like a
co-linear array of in-phase dipoles) was just the same as a halfwavelength
along a wire in an antenna without any standing waves (like a Beverage).

Unfortunately, that cannot be true. The maximum H-field amplitude at a current
null cannot possibly be the same as the maximum H-field where a current null
never exists.
--
73, Cecil http://www.qsl.net/w5dxp



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Unfortunately, that cannot be true. The maximum H-field amplitude at a
current
null cannot possibly be the same as the maximum H-field where a current
null
never exists.
============================

Dear Cec, your nitpicking is inexhaustible and at this time in the morning I
havn't the energy to sort out what you are talking about.

Best to agree to differ, eh? ;o)
---
Reg.

Reg Edwards wrote:
Dear Cec, your nitpicking is inexhaustible and at this time in the morning I
havn't the energy to sort out what you are talking about.

Best to agree to differ, eh? ;o)

I don't see how you can possibly assert that the fields are the same for
a standing-wave antenna and a traveling-wave antenna because they obviously
are not the same. A magnetic pickup at a current null on a standing-wave
antenna will read a low maximum value. A magnetic pickup at the same point
on a traveling-wave antenna will read a high maximum value.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:

An excellent and easy to follow description of the method of moments can
be found in Kraus' _Antennas_, Second Ed. I assume it's in the third
edition also, but it's not in the first. The NEC-2 manual recommends
R.F. Harrington, _Field Computation by Moment Methods_ (McMillan, 1968)
but I haven't seen this book.


I'm looking for a text to help me increase my understanding of antennas
beyond what is contained in the ARRL Antenna Handbook. It looks like
"Antennas" by Kraus is it. Can anyone recommend any others?

Thanks and 73,

--
* Do NOT use Reply *
Reply only through ARRL forwarding service to K3TD

Tad, K3TD

tad danley wrote:
I'm looking for a text to help me increase my understanding of antennas
beyond what is contained in the ARRL Antenna Handbook. It looks like
"Antennas" by Kraus is it. Can anyone recommend any others?

_Antenna_Engineering_Handbook_, edited by Jasik, contributions by many.

_Antenna_Theory_Analysis_and_Design_, by Balanis
--
73, Cecil http://www.qsl.net/w5dxp



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On Sun, 17 Aug 2003 13:56:11 GMT, tad danley
wrote:

Roy Lewallen wrote:


I've tried to point out on this thread that although the feedpoint
impedance is an impedance with the units of ohms, and the impedance of a
plane wave in free space also has the units of ohms, they're not the
same thing.


This may not be a good analogy, but Specific Impulse of rocket motors
helps me to remember that the 'units' of something have to be considered
in the context of what is being measured. Specific impulse is a measure
of the performance of a rocket motor. It measures the thrust obtained
from a single kilogram of propellant burned in one second. The 'units'
of Specific Impulse are seconds, but we're not measuring 'time'.

73,

Hi Tad,

Your point is well taken. ALL physical phenomenon can be expressed
through a chain of conversions in the MKS system of units. When
someone tells you that their terminology is inconsistent between
disciplines (as such offered in this and other threads); it must then
be amenable to reduction to MKS terms or one of the two conflicting
expressions is invalid.

That is to say to the specific matter about the usage of "ohms:"
Here, the unit of ohm must be reduced to Meters, Kilograms, and
Seconds for both usages (electrical and radiative). At that point,
both will have a common basis for comparison and if in fact their
reduced terms are identical, then their common usage is also
identical.

One simple example is with the measurement of body weight on the
bathroom scale (a torsion or compression device) as opposed to the
weight measured on the doctor's scale (a beam balance). Let's say
before you go to the doctor's, you weigh yourself in around 165
pounds. When you arrive at the doctor's, his scale says you weigh
around 75 kilograms.

Let's remove this same scenario to the moon (you live in one of those
futuristic 1990's colonies forecast by the space race back in the
60's). Before you went to the doctor's you weighed in around 33
pounds. When you arrive at the doctor's, his scale says you weigh
around 75 kilograms.

Here we find the expression "pounds" suffers what appears to be the
same plight of "ohms" in that the determination of a value is
inconsistent. You may also note constants of proportionality on earth
and the moon. These constants when expressed as a ratio also describe
the significant differences between the earth and the moon.

The problem is that the term "weight" has a hidden association to the
constant of Gravity. The expression Gram is one of Mass, not weight.
The expression pound is not an expression of Mass unless you expand it
to include the term for the particular constant of Gravity. Mass is
constant in the Newtonian Universe, and weight is not.

If you were to have reduced the pounds to the MKS system both times,
you would have found it consistent both times (here on earth, and on
the moon).

If you reduce the "ohms" to the MKS system both times.... Well I will
leave that for further deliberation as some are sure to be surprised.
:-)

73's
Richard Clark, KB7QHC

Roy Lewallen wrote in message ...

I've tried to point out on this thread that although the feedpoint
impedance is an impedance with the units of ohms, and the impedance of a
plane wave in free space also has the units of ohms, they're not the
same thing. Feedpoint impedance is the ratio of a current to a voltage.
Wave impedance, or the intrinsic impedance of a medium, is the ratio of
an E field to an H field -- it's also the square root of the ratio of
the medium's permeability to its permittivity. An antenna converts
currents and voltages to E and H fields, it doesn't just transform one
impedance to another. Hence my insistence on calling an antenna a
transducer rather than a transformer.


I've agreed with you on the semantics of antennas as transducers,
but two transducers DO make a transformer.

Ohms are still always Ohms, regardless of what you are measuring.
And it's very interesting that the E and H fields have units of
Volts/meter and Ampere(turn)/meter, which when you divide one by the
other, you get basically Volts/ampere, just like you would in a
transmission line.

But I don't claim that a wave traveling in a transmission line is
the same as a wave traveling through free space.


Slick

tad danley wrote:
Roy Lewallen wrote:


An excellent and easy to follow description of the method of moments
can be found in Kraus' _Antennas_, Second Ed. I assume it's in the
third edition also, but it's not in the first. The NEC-2 manual
recommends R.F. Harrington, _Field Computation by Moment Methods_
(McMillan, 1968) but I haven't seen this book.



I'm looking for a text to help me increase my understanding of antennas
beyond what is contained in the ARRL Antenna Handbook. It looks like
"Antennas" by Kraus is it. Can anyone recommend any others?

Thanks and 73,


Kraus is not only an antenna expert, he is a
world-class authority on the entire field of
Electromagnetics, based on Maxwell's equations.
His mathematics is elegant.

Bill W0IYH

....and his writing is lucid. I read his first edition, a gift from my
Father, and knew where I wanted to go to grad school. He is also a very
fine person.
Buy and read his books.
73 Mac N8TT
--
J. Mc Laughlin - Michigan USA
Home:

"William E. Sabin" sabinw@mwci-news wrote in message
...
snip

Kraus is not only an antenna expert, he is a
world-class authority on the entire field of
Electromagnetics, based on Maxwell's equations.
His mathematics is elegant.

Bill W0IYH

On Mon, 18 Aug 2003 11:28:40 -0700, Roy Lewallen
wrote:

. . .
An antenna is a structure that transforms Radiation Resistance into
the Impedance of free space, as shown, and by definition. Both use
identical MKS units, both are identical characteristics.

Sorry, that's a demonstrably absurd assertion.

Hi Roy,

although the feedpoint impedance is an impedance with the units of ohms,
and the impedance of a plane wave in free space also has the units of ohms,
they're not the same thing.

So, how do the "ohms" of free space differ from the "ohms" of a
quarter wave monopole's Radiation Resistance?

The demonstrables you offer do not enlighten us in what physical
constants these unique terms of your usage diverge from those in the
MKS system. As I pointed out in my posting, whatever derivation for
the characteristic Z of free space is, it must ultimately devolve to
the identical expression for the common Ohm.

I would offer by way of caution that the expression
Zc = (µ0 / e0)^0.5
where µ0 is expressed in Henrys per meter and
where e0 is expressed in Farads per meter;
that that, too, arrives at the same Ohms employed by carbon resistors
and Radiation Resistance.

This is much like trying to compare miles per gallon and kilometers
per liter. When push comes to shove, the reduction to MKS will reveal
that the same container of gas will get you down the same stretch of
asphalt the same distance no matter what mix of terms you substitute
for liquid volume and length. This goes to include offbeat
descriptive terms like miles per liter; kilometers per gallon; or
furlongs per hogshead for that identical container of gas. Solutions
of proportionality are not unique physical constants.

73's
Richard Clark, KB7QHC