"Roy Lewallen" wrote in message
...
You've said that because the inductor I chose is something like 4%
larger than necessary to resonate the antenna, the magnitude and phase
shift from input to output would be very nearly zero (although the
reasoning is contrary to conventional electrical circuit theory, and I
don't follow it at all).

Don't know. Didn't say it. Can't help.

So what I'm asking for is an inductor value
which would exhibit a large enough phase and/or magnitude shift that
would be easily seen in a measurement.

Do we agree that the amount of differential will depend on the number of
'degrees missing' from the length of the antenna?

Do we agree that the position of the loading coil plays a significant.
role in determining how much of a current differential will appear across
it?

I'll be constructing a more ideal
33 foot vertical in the near future, and making similar measurements at
3.8 MHz. So if its feedpoint impedance is, let's say, 35 - j370, what
would be the input to output current ratio (magnitude and phase) for a
physically very small base inductor of, say, +j300 ohms? If it's very
small, then pick an inductor value which would exhibit a substantial
inpututput current ratio.

Are you going to insist that it be one of these ferrite core jobs, or is it
more like ones on a HF6V?

73, Jim AC6XG

It sounds like the predictions are in. Among the several people who
believe that the current out of a small inductor doesn't equal the
current in, only Yuri was able to calculate a predicted value for the
test, of 2.5 - 5% reduction in current at the output compared to the
input, with a phase shift of about 18 degrees.

What I measured was a 3.1% reduction in magnitude from input to output,
with no discernible phase shift. The 3.1% is an average of two readings,
with the input and output probes exchanged. The output was smaller than
the input in both measurements, about 2% and 4%. So I believe there's a
real difference between output and input current, although with the
accuracy of my measurements, I only have reasonable confidence it's
somewhere between 1 and 5%. I can resolve about 2-3 degrees of phase
shift, though, and I couldn't discern any at all. (Yes, the scope
trigger was from one channel, not alternating.) So I have very high
confidence that Yuri's prediction of 18 degrees is incorrect.

I don't subscribe to the notion that the current out of a very small
inductor should be different than the current in due to some magical
property it acquires when connected to an antenna. My working hypothesis
is that the currrent difference I did see was due to stray capacitance,
either from the probes or simply to the Earth and other objects. It
would take an equivalent of 6.8 pF at the output of the coil (that is,
between the coil output and the current probe) to get 3% reduction, and
only about 1/3 that amount to see the minimum value of reduction of 1% I
estimate was actually present.

I repeated the test on the bench, with a 36 ohm resistor in series with
a 220 pF capacitor substituting for the antenna. The result was a 2.3%
output:input reduction, again with no discernible phase shift. This is
within the measurement error of being the same result. This is what
should be expected -- except for unintentional coupling to the antenna's
field, the inductor's environment is the same on the bench as at the
antenna base, in these single frequency, steady state tests. (That also
contradicts what some newsgroup participants have been claiming.)

So, although the small output:input current reduction was within Yuri's
prediction, the phase shift certainly wasn't. If time permits, I'll make
a more idealized antenna and repeat the measurements with a larger
inductor at the base of a more reactive antenna. I'll predict in advance
that if I double the amount of loading L, I'll approximately double the
amount of current magnitude attenuation -- that is, to somewhere around
6%. That's what should be expected if the cause of the attenuation is
stray C or a similar phenomenon.

I've added a picture to the
http://eznec.com/rraa/Inductor_Current_Measurement.html page, showing
the overall setup including the scope. It gives a little better
perspective on the relative sizes of various objects.

Roy Lewallen, W7EL

On Tue, 11 Nov 2003 13:14:56 -0500, Jack Smith
wrote:

On Tue, 11 Nov 2003 10:31:35 -0600, Cecil Moore
wrote:

The original argument was over whether a
75m bugcatcher coil, containing distributed resistance, inductance, and
capacitance, actually possesses those same characteristics in reality.

I apologize if I've misunderstood where this topic is at; it's been
very difficult to follow as it drifts back and forth.

Hi Jack,

No apology is required from you. This thread has a very specific
question from a single correspondent (Roy). The substituted topic
that you find confusion with is a common form of (Cecil's) not being
responsive to the topic by deflection to other issues. The comedy
consists of the "gentlemen's agreement" to not cut this short when
this occurs.

But such is the gamesmanship that is being conducted, from the start.
The withholding of data to embarrass correspondents is not uncommon.
Lord knows how many I've embarrassed with simpler topics (the current
crew being only a subset). However, I generally restrain my
participation such that those threads are smaller. Otherwise the
posting of:
On Tue, 11 Nov 2003 10:26:32 -0800, Roy Lewallen wrote:

Otherwise, the
thread would have been about two postings long.
which totals 75 (soon to be 76 with this), and for which Roy has
contributed very little new details, nor any data across the majority
of 27 of his own (appealing for inductor values to force the issue
would have made the thread three postings long, c'mon now) obviously
reveals that entertainment is being served. OK, OK, for the sake of
the mythical lurker, we can all give a wink and a nod that it is
"edutainment."

I hope none expect an Emmy for these sweeps. [I would like to thank
all my books and their authors; and especially the large supporting
cast, all the little people, for making this possible.]

73's
Richard Clark, KB7QHC

Jack Smith wrote:
My understanding of the particular question being debated is that the
loading coil is physically small and at the frequency in question may
be safely treated as a lumped element, and that some have said that
current-in current-out.

A 200 cubic inch 75m bugcatcher coil is NOT physically small and should
NOT be treated as a lumped element if one desires real-world results.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:
So what I'm asking for is an inductor value
which would exhibit a large enough phase and/or magnitude shift that
would be easily seen in a measurement.

How about a coil with 180 degree phase shift as described by Kraus?

"A coil can also act as a 180 degree phase shifter as in the collinear
array of 4 in-phase 1/2WL elements in Fig. 23-21b. Here the elements
present a high impedance to the coil which may be resonated without
an external capacitance due to its distributed capacitance. The coil
may also be thought of as a coiled-up 1/2WL element."

Here's the diagram in 23-21b

--------------coil-------------FP---------------coil----------------
1/2WL 1/2WL 1/2WL 1/2WL

The coils are designated as "Phase-reversing". Each coil occupies 1/2WL
electrically.

Have you never encountered phased arrays like the above or understood
that the coils are causing a 180 degree phase shift? That's the way
my Diamond 440 MHz mobile antenna works.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:
Anyone who understands basic circuit theory knows this. But that doesn't
include a number of the participants of this newsgroup. Otherwise, the
thread would have been about two postings long.

Too bad lumped inductors bear absolutely no resemblance in reality to
75m bugcatcher coils. Don't you believe Kraus when he says 180 degrees
of current phase shift can be accomplished by a single coil in a wire
antenna?

I once had an engineer like you working for me. He took four man-months
to engineer and breadboard a design that was over budget and out of spec.
I, a VP, turned out another design (from scratch) in one long weekend that
was under budget and exceeded the specs.
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Clark wrote:
This thread has a very specific
question from a single correspondent (Roy).

Huh? This thread is a direct result of W8JI's alleged assertion that
the current into a coil and out of a coil is always the same or else
Kirchhoff's law is violated. Here is the quote, allegedly from W8JI,
that started this whole discussion.

"If you look at HOW an inductor works, the current flowing in one terminal
ALWAYS equals the current flowing out the other terminal."

Have you been on vacation or what?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"Here is the diagram in 23-21b."

Thanks, Cecil. My copy of Kraus is new and I`d not yet read page 824.
Kraus says:

"The coil may also be thought of as a coiled-up halfwave element."

I like his preceding sentence:

"Here the elements present a high impedance to the coil which may be
resonated without external capacitance due to its distributed
capacitance."

A "phase reversing coil" does present a 180-degree phase shift between
its ends.

Best regards, Richard Harrison, KB5WZI

I, a VP, turned out another design (from scratch) in one long weekend that
was under budget and exceeded the specs.
--
73, Cecil http://www.qsl.net/w5dxp

====================================

A design which 'exceeds' specified performance is as poor as one which
'under exceeds'.

Significant deviations in either direction are sure indications of poor
engineering education and incompetence.

Both deviations are equally expensive and wasteful in terms of time,
materials and labour.

Even kids living with rats in the sewers of Rio de Janerio know this.

Rats themselves are highly intelligent, abundent, successful animals.

Should our campuses be transferred? ;o)
---
Reg.

Now, that's quite an insult, based on a total lack of information about
my career and what I've accomplished.

I'm going to do my best to ignore Cecil's postings from here on. They're
abusive and insulting. And any time he's asked for a number,
calculation, or equation to back his point of view, he dodges, ducks,
and diverts -- and insults.

Some of the readers are undoubtedly impressed by this. That's fine --
those readers won't benefit from my postings anyway.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

Anyone who understands basic circuit theory knows this. But that
doesn't include a number of the participants of this newsgroup.
Otherwise, the thread would have been about two postings long.


Too bad lumped inductors bear absolutely no resemblance in reality to
75m bugcatcher coils. Don't you believe Kraus when he says 180 degrees
of current phase shift can be accomplished by a single coil in a wire
antenna?

I once had an engineer like you working for me. He took four man-months
to engineer and breadboard a design that was over budget and out of spec.
I, a VP, turned out another design (from scratch) in one long weekend that
was under budget and exceeded the specs.