Funny, I've seen no one recommend addition of a 1:1 choke balun
near the
antenna feedpoint. If RF is flowing back down the shield of his
feedline, that surely could cause some incorrect readings on SWR in
the shack, wouldn't it? K7AAT




And, how well would rf flow back down the shield of
"buried 75 foot of RG213..." ? :-)

Jonesy



Apparently well enough to cause a problem. Its now 9 days
later from the above comment, and I see today that the original poster
followed my suggestion to install a balun which has solved his problem.


Ed K7AAT

Ed wrote in
. 192.196:

....
Apparently well enough to cause a problem. Its now 9 days
later from the above comment, and I see today that the original poster
followed my suggestion to install a balun which has solved his problem.

Ed, that defines how you define the problem.

If the problem was different measurements, that was caused by disturbing
the thing that was measured.

The different measurements hints another possible problem, common mode
feedline current. The baluns have changed the effect of those, and
probably differently at different frequencies.

But fundamentally, it is wiser to preserve the common mode current path
(even if you reckon the baluns help to reduce it) when making the
measurments.

The whole exercise demonstrates that the measurements from shack were
valid, it was disconnecting the feedline and making measurements at the
feedpoint that was invalid. (BTW, the measurements in the shack should be
done with the shield path connected as normal.)

A good example of the limited thinking in the proposition that you can
only make valid measurements at the feedpoint.

Owen

Cecil Moore wrote:
Michael Coslo wrote:
Well, I don't think we can cover the entire earth with water past the
height of the tallest mountains. Like that ever happened tho'.

The original languages, like our own version of English,
had numerous definitions of "earth". I can cover the
"entire earth" in my handful of earth with a pint of water.

At the time of that original tale, man had absolutely no
concept of a 8000 mile diameter "planet earth". "Earth"
was as far (and as flat) as one could see and I have seen
Texas floods, in my lifetime, where nothing but water
could be seen. :-) Heck, I have been sailing on Clear
Lake, out by NASA, when I couldn't see anything but
water in all directions.


Absolutely. No question that the great flood was a localized phenom. I
was just getting in my occasionall dig at those who would demand that
since it says so in one book, it had to have been the world.

The bible is mostly enjoyable reading as long as we don't get tripped
up on the whole literal thing.

- 73 de Mike N3LI -

On Sat, 02 Aug 2008 17:18:52 -0700, 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

Faraday cage.

JosephKK wrote:

...
Faraday cage.


Form a wire loop inside a Faraday Cage; Wave a strong neodymium magnet
about, outside the cage; You WILL get a reading ...

http://en.wikipedia.org/wiki/Faraday_cage

.... but, for electrostatic fields, they are dynamic.

Regards,
JS

JosephKK wrote:

...
Faraday cage.


Perhaps this will help:

http://www.lessemf.com/faq-shie.html#Lead-Copper

Regards,
JS