Vertical problem
 

"826" wrote in
:

Hi,
Sorry I didn't rely sooner. The weather hasn't been too good hear.
This
morning I disconnected the coax from the shack and measured the
antenna with the six foot length of coax. It looked OK. I then
connected just the shield of the long coax going to the shack and
still measuring with the short coax it shifted just like measured
before in the shack. I have then made up a choke balun and installed
it at the base of the antenna and it improved everything by about 60%.
I will now make another one for the shack end. I think everything is
under control now. Thanks to all for heading me in the right
direction. Vern M0WQR

Vern, whilst the choke made a difference, the fact that there remains a
difference in the feedpoint impedance with the shield connected and
disconnected, even when using the choke, indicates that there is some
effects observable from common mode feed line current in your scenario.

If you want a measurement of the antenna as it would be used, measure it
as it would be used... make sure the shield current path is as it would
be used.

Owen

Vertical problem
 

On Sun, 27 Jul 2008 21:07:25 -0700, John Smith
wrote:

Ed wrote:

...
About as well as it flows up the center conductor, possibly. You
don't think that just because the cable is buried that RF flow on the
shield conductor is prevented, do you?

Ed

I sure can imagine one heck of a "capacitive load" on that outer
conductor to ground! What, thousands/tens-of-thousands of pf?

Regards,
JS

95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.

Vertical problem
 

JosephKK wrote:

...
95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


Or, simply put, for ever action, an equal and opposite reaction occurs
.... yes, basic physics ... however, what is in question--since the other
braid has and "inside" and an "outside", where does that equal opposite
reaction occur ...

Regard,
JS

Vertical problem
 

John Smith wrote:
JosephKK wrote:

...
95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


Or, simply put, for ever action, an equal and opposite reaction occurs
... yes, basic physics ... however, what is in question--since the other
braid has and "inside" and an "outside", where does that equal opposite
reaction occur ...

Regard,
JS


Gawd, I am getting hasty in my old age ...

No electrical field can occur without a magnet field, no magnetic field
can occur with out a corresponding electrical component, again, basic
physics; you are attempting to say the magnetic component of the
current on the outside of the braid is NOT SEEN by the center conductor
.... that may be in error ... but, I would be willing to listen how
tinned copper (the braid) is some sort of shield to magnetic fields ...

Regards,
JS

Vertical problem
 

John Smith wrote:
John Smith wrote:
JosephKK wrote:

...
95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


Or, simply put, for ever action, an equal and opposite reaction occurs
... yes, basic physics ... however, what is in question--since the
other braid has and "inside" and an "outside", where does that equal
opposite reaction occur ...

Regard,
JS


Gawd, I am getting hasty in my old age ...

No electrical field can occur without a magnet field, no magnetic field
can occur with out a corresponding electrical component, again, basic
physics; you are attempting to say the magnetic component of the
current on the outside of the braid is NOT SEEN by the center conductor
... that may be in error ... but, I would be willing to listen how
tinned copper (the braid) is some sort of shield to magnetic fields ...

Regards,
JS

Geesh, too old, I am telling you ...

Disregard "static fields", however, that is NOT what is in question here ...

Regards,
JS

Vertical problem
 

JosephKK wrote:

95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


It's unfortunate that this isn't true. If it were, it would make our
lives a lot easier. Anyone interested in learning more about this topic
might take a look at http://eznec.com/Amateur/Articles/Baluns.pdf.

Roy Lewallen, W7EL

Vertical problem
 

"John Smith" wrote in message
...
John Smith wrote:
John Smith wrote:
JosephKK wrote:

...
95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


Or, simply put, for ever action, an equal and opposite reaction occurs
... yes, basic physics ... however, what is in question--since the other
braid has and "inside" and an "outside", where does that equal opposite
reaction occur ...

Regard,
JS


Gawd, I am getting hasty in my old age ...

No electrical field can occur without a magnet field, no magnetic field
can occur with out a corresponding electrical component, again, basic
physics; you are attempting to say the magnetic component of the current
on the outside of the braid is NOT SEEN by the center conductor ... that
may be in error ... but, I would be willing to listen how tinned copper
(the braid) is some sort of shield to magnetic fields ...

Regards,
JS

Geesh, too old, I am telling you ...

Disregard "static fields", however, that is NOT what is in question here
...

Regards,
JS

---------

Rats! You beat me to it!

Ed, NM2K

Vertical problem
 

Ed Cregger wrote:

...
Rats! You beat me to it!

Ed, NM2K



It's about time! Some of these guys have held my feet to the fire!

:-)

Regards,
JS

Vertical problem
 

Basic physics is fine, but it's possible to reach all sorts of invalid
conclusions if misapplied.

Roy Lewallen, W7EL

Vertical problem
 

Roy Lewallen wrote:
Basic physics is fine, but it's possible to reach all sorts of invalid
conclusions if misapplied.

Roy Lewallen, W7EL

I have been thinking about this "comment."

And, absolutely!; Things only get more interesting when we can "bend"
the laws ... ;-)

Regards,
JS