John Ferrell wrote:
. . .
I am a perpetual antenna student!

And so are we all.

Roy Lewallen, W7EL

I found the error, I had to fix two conditions that I had changed in the
model:

Copper wire (for loss)
Ground characteristics

Now that both antennas have the same conditions, the T has ever so slightly
better gain at 20 degrees than the Inverted L. Not enough to bother with the
increased complexity, and the input Z is now down around 5 ohms for the T
and 8 ohms for the L.

Now, is it worth matching the 8 ohms up to 50 at the feedpoint, or just
using the tuner in the shack to take care of it? (coax feed, LMR-400, about
50')

....hasan, N0AN

"Roy Lewallen" wrote in message
...
John Ferrell wrote:
. . .
I am a perpetual antenna student!

And so are we all.

Roy Lewallen, W7EL

Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the feedline
to antenna at the antenna feed point. Any attempt to match the feedline with a
tuner in the shack only turns the whole feedline into part of the antenna
system. By doing that you have lost any good work in building the antenna.

Dan

hasan schiers wrote:
I found the error, I had to fix two conditions that I had changed in the
model:

Copper wire (for loss)
Ground characteristics

Now that both antennas have the same conditions, the T has ever so slightly
better gain at 20 degrees than the Inverted L. Not enough to bother with the
increased complexity, and the input Z is now down around 5 ohms for the T
and 8 ohms for the L.

Now, is it worth matching the 8 ohms up to 50 at the feedpoint, or just
using the tuner in the shack to take care of it? (coax feed, LMR-400, about
50')

...hasan, N0AN

"Roy Lewallen" wrote in message
...

John Ferrell wrote:

. . .
I am a perpetual antenna student!

And so are we all.

Roy Lewallen, W7EL

dansawyeror wrote:
Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the
feedline to antenna at the antenna feed point.

Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?

Any attempt to match the
feedline with a tuner in the shack only turns the whole feedline into
part of the antenna system.

Simply not true if the currents remain differentially balanced.
SWR doesn't cause feedline radiation.
--
73, Cecil http://www.qsl.net/w5dxp


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Let's take the case of a 50 Ohm line and some mismatched antenna. The result is
a combination other then 50 Ohm with most likely a zero complex component. All a
tuner does is match 50 Ohm at the radio to the complex impedance presented to it
at the source of the line.

That the only place with 50 Ohms and zero inductance in the line - antenna
system. The combination of cable and antenna presents something other then R =
50 ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.

Dan

Cecil Moore wrote:
dansawyeror wrote:

Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the
feedline to antenna at the antenna feed point.


Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?

Any attempt to match the feedline with a tuner in the shack only turns
the whole feedline into part of the antenna system.


Simply not true if the currents remain differentially balanced.
SWR doesn't cause feedline radiation.

dansawyeror wrote:
The combination of cable and antenna presents something
other then R = 50 ohms 0 reactance and the the transmission line see
discontinuities. The result is it radiates.

If the currents are balanced, a 50 ohm transmission line seeing
something other than a 50 ohm load does NOT cause it to radiate.
If a 50 ohm unbalanced transmission line sees a 50 ohm balanced
load and common-mode currents flow on the outside of the coax,
it will usually result in radiation from the feedline. Simply
knowing the magnitude of the feedpoint impedance doesn't tell us
anything about feedline radiation.
--
73, Cecil http://www.qsl.net/w5dxp


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"Cecil Moore" wrote in message
...
dansawyeror wrote:
The combination of cable and antenna presents something other then R = 50
ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.

If the currents are balanced, a 50 ohm transmission line seeing
something other than a 50 ohm load does NOT cause it to radiate.
If a 50 ohm unbalanced transmission line sees a 50 ohm balanced
load and common-mode currents flow on the outside of the coax,
it will usually result in radiation from the feedline. Simply
knowing the magnitude of the feedpoint impedance doesn't tell us
anything about feedline radiation.
--
73, Cecil http://www.qsl.net/w5dxp

Even grossly mismatched open wire transmission line does not radiate
significantly. For example a 66 ft length of 3" spaced, open wire line,
shorted at one end, radiates only 4 - 5% of the input power. 95% is
dissipated in the conductor losses.

73,

Frank

On Sat, 27 Aug 2005 16:53:39 -0700, dansawyeror
wrote:

Let's take the case of a 50 Ohm line and some mismatched antenna. The result is
a combination other then 50 Ohm with most likely a zero complex component.

Surely you don't believe this do you? It is -much- more likely that
the impedance is reactive than not. At one (fundamental) frequency
the reactance is zero. At every other frequency it is reactive.

All a
tuner does is match 50 Ohm at the radio to the complex impedance presented to it
at the source of the line.

Isn't that enough?


That the only place with 50 Ohms and zero inductance in the line - antenna
system. The combination of cable and antenna presents something other then R =
50 ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.

Oh dear me.

Wes,

As a starter, look at this site:

http://www.cbtricks.com/~ab7if/coax/coax.htm

When a transmission line is terminated in it's characteristic impedance there is
no voltage or current reflection from the line. The electromagnetic fields
continue to flow into the termination as if the line were infinitely long. When
a mismatch of impedance occurs, reflected waves will be produced and they will
interact with the incident waves. The total voltage and current on the line are
no longer the result of a single traveling wave from the source to the load.
Instead, it is the algebraic sum of two waves traveling in opposite directions.
This interaction results in what is known as standing waves. The waves remain in
fixed positions along the line while they vary in amplitude and polarity. A wave
of any shape can be transmitted along the line without any change of waveshape
or magnitude. Looking at the gif below, we see a line driven with a sine wave
generator, terminated with a short circuit to maximize the reflection.

My first claim is a tuner at the source does not materially improve what is
happening in the coax. That is a tuner does not recreate the condition above
where the coax is functioning as a properly matched and terminated transmission
line. All the tuner does is match the impedance at the coax source back to some
known, usually 50 Ohm, value.

My second claim is when the mismatch condition at the coax destination, i.e.
antenna that may result in significant radiation from the coax itself.

Dan

Wes Stewart wrote:
On Sat, 27 Aug 2005 16:53:39 -0700, dansawyeror
wrote:


Let's take the case of a 50 Ohm line and some mismatched antenna. The result is
a combination other then 50 Ohm with most likely a zero complex component.


Surely you don't believe this do you? It is -much- more likely that
the impedance is reactive than not. At one (fundamental) frequency
the reactance is zero. At every other frequency it is reactive.


All a
tuner does is match 50 Ohm at the radio to the complex impedance presented to it
at the source of the line.


Isn't that enough?


That the only place with 50 Ohms and zero inductance in the line - antenna
system. The combination of cable and antenna presents something other then R =
50 ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.


Oh dear me.

Wes,

As a starter, look at this site:

http://www.cbtricks.com/~ab7if/coax/coax.htm

When a transmission line is terminated in it's characteristic impedance there is
no voltage or current reflection from the line. The electromagnetic fields
continue to flow into the termination as if the line were infinitely long. When
a mismatch of impedance occurs, reflected waves will be produced and they will
interact with the incident waves. The total voltage and current on the line are
no longer the result of a single traveling wave from the source to the load.
Instead, it is the algebraic sum of two waves traveling in opposite directions.
This interaction results in what is known as standing waves. The waves remain in
fixed positions along the line while they vary in amplitude and polarity. A wave
of any shape can be transmitted along the line without any change of waveshape
or magnitude. Looking at the gif below, we see a line driven with a sine wave
generator, terminated with a short circuit to maximize the reflection.

My first claim is a tuner at the source does not materially improve what is
happening in the coax. That is a tuner does not recreate the condition above
where the coax is functioning as a properly matched and terminated transmission
line. All the tuner does is match the impedance at the coax source back to some
known, usually 50 Ohm, value.

My second claim is when the mismatch condition at the coax destination, i.e.
antenna that may result in significant radiation from the coax itself.

Dan

Wes Stewart wrote:
On Sat, 27 Aug 2005 16:53:39 -0700, dansawyeror
wrote:


Let's take the case of a 50 Ohm line and some mismatched antenna. The result is
a combination other then 50 Ohm with most likely a zero complex component.


Surely you don't believe this do you? It is -much- more likely that
the impedance is reactive than not. At one (fundamental) frequency
the reactance is zero. At every other frequency it is reactive.


All a
tuner does is match 50 Ohm at the radio to the complex impedance presented to it
at the source of the line.


Isn't that enough?


That the only place with 50 Ohms and zero inductance in the line - antenna
system. The combination of cable and antenna presents something other then R =
50 ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.


Oh dear me.