Cecil Moore wrote:
wrote:
I expect that the situation with a long wire exiting the bottom will
couple MUCH more energy into the center conductor.

My suggested solution over on eHam.net included RF chokes
and RF bypass caps at each end of the tubing.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil,

You put great faith in passing you Mensa exam.

With that in mind, what possible difference does the shield make once
the inner conductor is bypassed and choked at each end?

In case you can't understand, the answer is NO difference.

Without the chokes and bypasses, your idea won't work. With the chokes
and bypasses, the idea isn't needed. The relay wire can run right down
the mast with no ill effects.

It's so basic and simple, even a Mensa member can follow it!

73 Tom

I should have said "the more RF chokes there are, the less current will
flow in the center conductor of the case where the wire is inside the
shield" by the way.

If the RF chokes and wire are inside the shield, it will keep the
current off the wire inside the shield.

However, where the wire exits the shield, currents can still be induced
on it... this is what allows current to flow on the unchoked center
conductor, right? So why wouldn't it flow in the other direction.

So you need chokes some distance outside the shield to isolate the rest
of the wire from the antenna.

If you put the wire outside the shield and put chokes at the top and
bottom, some distance away from the antenna, then a very large current
will be induced on the wire between the chokes compared to the current
you get on the wire inside the shield. However, this doesn't
immediately translate into more current on the control wire trailing
away. It is just saying something about the wire between the top and
bottom chokes.

What you're trying to do is decouple the control wire going away from
the antenna from the antenna. Decoupling the control wire that runs up
inside or outside of the antenna isn't very important as long as
current doesn't flow on the control wire to the shack.

Whether or not inside or outside of the tower/tube helps depends on a
lot of factors and should be answered with some sort of calculation...

Seems that the various claims are testable...

I'll post anything I come up with.

Dan

I modeled the original question Cecil asked on r.r.a.a. (current on a
coax center conductor of a monopole made of coax) because I was curious
and because my wetware simulation for the amount of RF coupled into the
end of a piece of coaxial cable wasn't up to the task. I didn't start
with the eHam question in mind.

I don't know offhand how much the coupling between the center conductor
and shield is at the ends of the coax, so I tried some stuff with the
only electromagnetic code I have lying around my house.

The relay question is not very interesting, it's just an engineering
one.. throw good chokes at it. Done. I agree.

I wanted to know what the current was in the center conductor of a
piece of RG-8 being used as a monopole. The answer to that question is
not trivially calculable, though it might be trivial in the sense of
being trivia... who cares? I did.

Dan

wrote:
You put great faith in passing you Mensa exam.

This member of MENSA is having difficulty in parsing
your statement. What does, "you Mensa exam", actually
mean? Does the pronoun, "you", address the Mensa exam?
Wouldn't it be better to address the Mensa exam as an
"it" rather than as a person? Your numerous deviations from
the accepted laws of physics and accepted English language
construction have me confused.

With that in mind, what possible difference does the shield make once
the inner conductor is bypassed and choked at each end?

What I said is that, contrary to your strange assertions, is that
the RF chokes and RF bypass capacitors block the stub function
upon which your entire argument rests. The result of my suggestion
is *NOT* a stub function as you have so stubbornly insisted. So I
ask you once again: Please prove that a stub with two RF chokes in
the conductive path is actually functional as a stub. If you cannot,
your entire argument falls apart.
--
73, Cecil http://www.qsl.net/w5dxp

wrote:
The suggestion of enclosing the wire in a shield was useless in that
application.

I have done such many times in my 55 years of being a ham.
It is NOT useless.
--
73, Cecil http://www.qsl.net/w5dxp

wrote:
If the RF chokes and wire are inside the shield, it will keep the
current off the wire inside the shield.

I hope W8JI is reading this. He insists that it will still
function as a stub and such an approach is "useless".

However, where the wire exits the shield, currents can still be induced
on it... this is what allows current to flow on the unchoked center
conductor, right? So why wouldn't it flow in the other direction.

So you need chokes some distance outside the shield to isolate the rest
of the wire from the antenna.

Just outside the shield is a relay with an RF bypass cap
across its coil.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
wrote:
If the RF chokes and wire are inside the shield, it will keep the
current off the wire inside the shield.

I hope W8JI is reading this. He insists that it will still
function as a stub and such an approach is "useless".

However, where the wire exits the shield, currents can still be induced
on it... this is what allows current to flow on the unchoked center
conductor, right? So why wouldn't it flow in the other direction.

So you need chokes some distance outside the shield to isolate the rest
of the wire from the antenna.

Just outside the shield is a relay with an RF bypass cap
across its coil.
--
73, Cecil http://www.qsl.net/w5dxp

Turn in your mensa membership card Cecil.

You flunked basic grade-K problem solving logic.

:-)

wrote:
I wanted to know what the current was in the center conductor of a
piece of RG-8 being used as a monopole. The answer to that question is
not trivially calculable, though it might be trivial in the sense of
being trivia... who cares? I did.

I have used that same circuit to switch a top hat
in and out. How much RF power did I lose by taking
that route?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
wrote:
I wanted to know what the current was in the center conductor of a
piece of RG-8 being used as a monopole. The answer to that question is
not trivially calculable, though it might be trivial in the sense of
being trivia... who cares? I did.

I have used that same circuit to switch a top hat
in and out. How much RF power did I lose by taking
that route?

That is NOTHING like the problem the ZL on eHam had.

wrote:
Cecil Moore wrote:
I have used that same circuit to switch a top hat
in and out. How much RF power did I lose by taking
that route?

That is NOTHING like the problem the ZL on eHam had.

Clutching at straws, are we? It's exactly like the ZL problem
except the relay is used to switch a top hat instead of a wire.
--
73, Cecil http://www.qsl.net/w5dxp