When measuring the SWR of a transmission line we can find a length
that is resonant. Or in other words the current is of an exact
sinusoidal form and thus the basis of SWR. When we apply the same
principles to a radiator
we cannot assume a perfect sinusoidal wave because of the field
generated outside the radiator where a degradation of amplitude
depends not only on the generated fields but also the length of the
radiator i.e a thin radiator. Thus one can see that a fractional wave
antenna if reflected as generally assumed cannot possibly be 1:1 for a
wavelength as per a perfect reflection as could or would be seen from
a transmississsion line.
The above not only shows that a transmission line is a closed circuit
as is a fractional wavelength antenna where the current travels on the
inside of the radiator and where the transmission line has current
flow on the inside of the
outer skin (brading) The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current in a
radiator is sinusoidal where as we all know that the current degrades
in aplitude dependent on radiator length. It should be seen that when
we use the term SWR we are looking at two different things, a
transmission line which is not radiating( ignoring leakage) but still
a closed circuit and a radiator that is radiating but with a non
sinusoidal current which is contrary to the assumptions made for MoM
style radiator programs. Thus it should be seen that any radiator is a
closed circuit with continuous leakage in current levels dependent on
its length via accountability for all four fouces present..
Regards
Art

"Art Unwin" wrote in message
...
When measuring the SWR of a transmission line we can find a length
that is resonant. Or in other words the current is of an exact
sinusoidal form and thus the basis of SWR. When we apply the same
principles to a radiator
we cannot assume a perfect sinusoidal wave because of the field
generated outside the radiator where a degradation of amplitude
depends not only on the generated fields but also the length of the
radiator i.e a thin radiator. Thus one can see that a fractional wave
antenna if reflected as generally assumed cannot possibly be 1:1 for a
wavelength as per a perfect reflection as could or would be seen from
a transmississsion line.
The above not only shows that a transmission line is a closed circuit
as is a fractional wavelength antenna where the current travels on the
inside of the radiator and where the transmission line has current
flow on the inside of the
outer skin (brading) The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current in a
radiator is sinusoidal where as we all know that the current degrades
in aplitude dependent on radiator length. It should be seen that when
we use the term SWR we are looking at two different things, a
transmission line which is not radiating( ignoring leakage) but still
a closed circuit and a radiator that is radiating but with a non
sinusoidal current which is contrary to the assumptions made for MoM
style radiator programs. Thus it should be seen that any radiator is a
closed circuit with continuous leakage in current levels dependent on
its length via accountability for all four fouces present..
Regards
Art

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current distribution.
The radiated field is then calculated based on the current distribution.

Frank

"Frank" wrote in message
news:toE5l.932$z%.775@edtnps82...

"Art Unwin" wrote in message
...
When measuring the SWR of a transmission line we can find a length
that is resonant. Or in other words the current is of an exact
sinusoidal form and thus the basis of SWR. When we apply the same
principles to a radiator
we cannot assume a perfect sinusoidal wave because of the field
generated outside the radiator where a degradation of amplitude
depends not only on the generated fields but also the length of the
radiator i.e a thin radiator. Thus one can see that a fractional wave
antenna if reflected as generally assumed cannot possibly be 1:1 for a
wavelength as per a perfect reflection as could or would be seen from
a transmississsion line.
The above not only shows that a transmission line is a closed circuit
as is a fractional wavelength antenna where the current travels on the
inside of the radiator and where the transmission line has current
flow on the inside of the
outer skin (brading) The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current in a
radiator is sinusoidal where as we all know that the current degrades
in aplitude dependent on radiator length. It should be seen that when
we use the term SWR we are looking at two different things, a
transmission line which is not radiating( ignoring leakage) but still
a closed circuit and a radiator that is radiating but with a non
sinusoidal current which is contrary to the assumptions made for MoM
style radiator programs. Thus it should be seen that any radiator is a
closed circuit with continuous leakage in current levels dependent on
its length via accountability for all four fouces present..
Regards
Art

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current distribution.
The radiated field is then calculated based on the current distribution.

Frank

art doesn't know MOM from the fractal least squares genetic optimizer
code... so don't be surprised when he comes back with more gibberish.

On Dec 27, 11:46*pm, "Frank" wrote:
"Art Unwin" wrote in message

...



When measuring the SWR of a transmission line we can find a length
that is resonant. Or in other words the current is of an exact
sinusoidal form and thus the basis of SWR. When we apply the same
principles to a radiator
we cannot assume a perfect sinusoidal wave because of the field
generated outside the radiator where a degradation of amplitude
depends not only on the generated fields but also the length of the
radiator i.e a thin radiator. Thus one can see that a fractional wave
antenna if reflected as generally assumed cannot possibly be 1:1 for a
wavelength as per a perfect reflection as could or would be seen from
a transmississsion line.
The above not only shows that a transmission line is a closed circuit
as is a fractional wavelength antenna where the current travels on the
inside of the radiator and where the transmission line has current
flow on the inside of the
outer skin (brading) The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current in a
radiator is sinusoidal where as we all know that the current degrades
in aplitude dependent on radiator length. It should be seen that when
we use the term SWR we are looking at two different things, a
transmission line which is not radiating( ignoring leakage) but still
a closed circuit and a radiator that is radiating but with a non
sinusoidal current which is contrary to the assumptions made for MoM
style radiator programs. Thus it should be seen that any radiator is a
closed circuit with continuous leakage in current levels dependent on
its length via accountability for all four fouces present..
Regards
Art

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; *it computes the current distribution.
The radiated field is then calculated based on the current distribution.

Frank

Yes it does but as always one must review the basis on which formula
is formed and conditions expressed
One of these conditions is that current flow is sinusoidal which
cannot be true because of leakage ( radiation)
per unit length of the radiator. If on compares the current flow of a
full wave radiatior to a fractional wave
current flow this becomes very obvious especially when either of them
is compared to a true sino soidal curve
Cheers Frank

On Dec 28, 8:20*am, "Dave" wrote:
"Frank" wrote in message

news:toE5l.932$z%.775@edtnps82...



"Art Unwin" wrote in message
...
When measuring the SWR of a transmission line we can find a length
that is resonant. Or in other words the current is of an exact
sinusoidal form and thus the basis of SWR. When we apply the same
principles to a radiator
we cannot assume a perfect sinusoidal wave because of the field
generated outside the radiator where a degradation of amplitude
depends not only on the generated fields but also the length of the
radiator i.e a thin radiator. Thus one can see that a fractional wave
antenna if reflected as generally assumed cannot possibly be 1:1 for a
wavelength as per a perfect reflection as could or would be seen from
a transmississsion line.
The above not only shows that a transmission line is a closed circuit
as is a fractional wavelength antenna where the current travels on the
inside of the radiator and where the transmission line has current
flow on the inside of the
outer skin (brading) The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current in a
radiator is sinusoidal where as we all know that the current degrades
in aplitude dependent on radiator length. It should be seen that when
we use the term SWR we are looking at two different things, a
transmission line which is not radiating( ignoring leakage) but still
a closed circuit and a radiator that is radiating but with a non
sinusoidal current which is contrary to the assumptions made for MoM
style radiator programs. Thus it should be seen that any radiator is a
closed circuit with continuous leakage in current levels dependent on
its length via accountability for all four fouces present..
Regards
Art

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; *it computes the current distribution.
The radiated field is then calculated based on the current distribution..

Frank

art doesn't know MOM from the fractal least squares genetic optimizer
code... so don't be surprised when he comes back with more gibberish.

David there is nothing technical to respond to in your posting so
what
sort of response were you looking for?. If MoM has the condition
stated in
the ARRL compendium then something is seriously wrong with antenna
programs!
Regards
Art

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current distribution.
The radiated field is then calculated based on the current distribution.

Frank

Yes it does but as always one must review the basis on which formula
is formed and conditions expressed
One of these conditions is that current flow is sinusoidal which
cannot be true because of leakage ( radiation)
per unit length of the radiator. If on compares the current flow of a
full wave radiatior to a fractional wave
current flow this becomes very obvious especially when either of them
is compared to a true sino soidal curve
Cheers Frank

None of the conditions assume current (distribution) on a radiator is
sinusoidal. It can be anything, not even remotely sinusoidal, and
frequently has discontinuities (such as a "unit step function" in the
case of a shunt fed, gamma matched, grounded tower, for example).

The theory behind the "Moment method", in the case of NEC 2,
is in the public domain, and available he

http://www.nec2.org/other/nec2prt1.pdf

Frank

On Dec 28, 11:06*am, "Frank" wrote:
The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current distribution.
The radiated field is then calculated based on the current distribution.

"Art Unwin" wrote in message
...
Using just one example radiation
at present is presumed to provide many waves along a conductor purely
on the bases that current is reflected from the antenna end and
progresses along the same path that it arrived. This error alone has
allowed many assumptions and erronious theories to be expanded.

oh no! now he doesn't believe in reflections! how could we ever survive on
here without endless discussions of reflections and waves?

"Art Unwin" wrote
The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current
in a radiator is sinusoidal where as we all know that the current
degrades in aplitude dependent on radiator length.
_____________

Art, the current distribution along even the shortest (fractional
wavelength), constant OD radiator also is ~sinusoidal.

Currrent always is near zero at the open end of a linear radiator of every
physical length. The shape of the current wave formed along a very short
radiator appears to be very close to triangular. But in fact that
"triangular" current distribution is just a very short section of a
sinusoidal waveform.

N.B. that MoM programs show exactly this for radiators that are very short
in terms of electrical wavelengths. This also is proven mathematically in
the antenna engineering textbooks of Kraus, Balanis, Johnson & Jasik, etc
etc.

RF

** Posted from http://www.teranews.com **

"Art Unwin" wrote
The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current
in a radiator is sinusoidal where as we all know that the current
degrades in aplitude dependent on radiator length.
_____________

Art, the current distribution along even the shortest fractional
wavelength, constant OD radiator also is ~sinusoidal.

Current always is near zero at the open end of a linear radiator of
every
physical length. The shape of the current wave formed along a very
short
radiator appears to be very close to triangular. But in fact that
"triangular" current distribution is just a very short section of a
sinusoidal waveform.

N.B. that MoM programs show exactly this for radiators that are very
short
in terms of electrical wavelengths. This also is proven
mathematically in
the antenna engineering texts of Kraus, Balanis, Johnson & Jasik,
etc.

RF