On Mon, 10 Nov 2003 00:50:55 -0800, Roy Lewallen
wrote:

Ok. So far, we have your calculation that the output current should be
5% smaller, and 18 degrees shifted in phase (lagging, I presume) from
the input; and Cecil's, that the output current should equal the
current, both in phase and magnitude. I don't know if Richard is going
to do the calculation or not, so I'll wait a little longer. Anyone else
like to hazard a prediction?

Roy Lewallen, W7EL

(1) Input current = output current
(2) No phase shift.

If you model the circuit using the lumped values for the antenna R and
jX components it's easy to see this.

Anyone not believing this can try modeling the base inductor as:
O----[0.3 ohms R']--[+j192 ohms]---[0.3 ohms R'']----0
Put current through it using your favorite SPICE simulator and compare
the current through the R' and the R''. The two plots coincide.





Jack K8ZOA

Roy, W7EL wrote:
"---feedpoint impedance of 35-j370 at 3.8 MHz. Choose an inductor value
and let me know what the output : input current ratio would be for that
inductor at the base of the antenna. Assume that the inductor is
physically small."

I`ll assume the inductor has no resistance, loss or radiation.

No loss or radiation means the inductance only delays current in the
antenna circuit by the phase angle impedance makes with resistance in
the circuit.

We need 370 ohms of inductive reactance to counteract the capacitive
reactance of the too short antenna. That calculates to 10.926
microhenry.

The current into the resonant antenna circuit is E/R = E/35

The current into the too short antenna alone is E/Z = E/ 371.65

The output : input ratio of the inductor is very nearly one because the
coil is lossless and its size is insignificant in terms of wavelength.

Best regards, Richard Harrison, KB5WZI

Jack Smith wrote:
(1) Input current = output current
(2) No phase shift.

If you model the circuit using the lumped values for the antenna R and
jX components it's easy to see this.

Anyone not believing this can try modeling the base inductor as:
O----[0.3 ohms R']--[+j192 ohms]---[0.3 ohms R'']----0
Put current through it using your favorite SPICE simulator and compare
the current through the R' and the R''. The two plots coincide.

We know what the model says. The original argument was over whether a
75m bugcatcher coil, containing distributed resistance, inductance, and
capacitance, actually possesses those same characteristics in reality.
A statement by a ham over on eham.net triggered the argument:

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

That is how a lumped inductor works in a model. That is not how a distributed
inductor works in reality.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:
And, Art, I'm surprised at your objecting to my bringing up the dreaded
complexity of -- gasp -- phase.

Here's a bench experiment that could be done concerning phase.
Create artificial standing waves with two signal generators equipped
with circulator loads (SGCL).

I1 I2
SGCL1----coil----SGCL2

Vary the phase of one of the signal generators while monitoring the
total current at each end of the coil. The equation for the total
current will be similar to the equation for total current in a
standing wave antenna, i.e. the phasor difference of I1 - I2. The
delay through the coil takes the two currents in opposite phase
directions.
--
73, Cecil http://www.qsl.net/w5dxp



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"Roy Lewallen" wrote in message
...
Jim, it sounds like you're firmly in the camp that believes that a phase
and/or magnitude shift will occur from one terminal to the other of a
physically very small inductor.

Physically very small.........what is that? Is it an inductor that behaves
as if it has no physical dimensions? Does it comprise a coil of wire that
has zero length?

Perhaps you can also propose an inductor I can put at
the base of a short antenna that would guarantee a large phase shift
which would be large and easily seen in a measurement.

How about if I just refer you to one of the many manufacturers of such
things?

73, Jim AC6XG


Roy Lewallen, W7EL

Jim Kelley wrote:
"Roy Lewallen" wrote in message
...

I did read what you said. You said that it wouldn't exhibit a phase
shift if placed at a current maximum. The current at the base of a short
vertical antenna is at its maximum there. So now if you're saying that
it *won't* exhibit a phase shift if placed at the base of a short
antenna, let's try this.


Naturally, the inductance of the coil and the resistance of the circuit
determine how much of a phase shift there will be. But the amount of
resulting change in current magnitude will depend on where on the cosine
curve this shift occurs. A 10 degree phase shift from 40 to 50 degrees
generates almost an order of magnitude greater change in current that it
does shifting from 0 to 10 degrees. Obviously, the closer the center
of
the coil is to zero (or 180) degrees, the smaller the resulting
differential
in current across the coil.

73, Jim AC6XG

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

Jack Smith wrote:
(1) Input current = output current
(2) No phase shift.

If you model the circuit using the lumped values for the antenna R and
jX components it's easy to see this.

Anyone not believing this can try modeling the base inductor as:
O----[0.3 ohms R']--[+j192 ohms]---[0.3 ohms R'']----0
Put current through it using your favorite SPICE simulator and compare
the current through the R' and the R''. The two plots coincide.

We know what the model says. The original argument was over whether a
75m bugcatcher coil, containing distributed resistance, inductance, and
capacitance, actually possesses those same characteristics in reality.
A statement by a ham over on eham.net triggered the argument:

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

That is how a lumped inductor works in a model. That is not how a distributed
inductor works in reality.


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.

The fact that the small coil is connected to an antenna which is not
physically small is immaterial.

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


Jack

Jim Kelley wrote:
"Roy Lewallen" wrote in message
...

Jim, it sounds like you're firmly in the camp that believes that a phase
and/or magnitude shift will occur from one terminal to the other of a
physically very small inductor.


Physically very small.........what is that? Is it an inductor that behaves
as if it has no physical dimensions? Does it comprise a coil of wire that
has zero length?


Perhaps you can also propose an inductor I can put at
the base of a short antenna that would guarantee a large phase shift
which would be large and easily seen in a measurement.


How about if I just refer you to one of the many manufacturers of such
things?

73, Jim AC6XG

I was looking for a value, not a part number.

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). 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. 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.

Roy Lewallen, W7EL

Hm. Let's suppose the inductor had a loss resistance of, say, 35 ohms
(equal to the resistive part of the antenna input Z). What would the
ratio be then? This is assuming the loss is dissipative and not "loss"
due to radiation.

Roy Lewallen, W7EL

Richard Harrison wrote:
. . .
The output : input ratio of the inductor is very nearly one because the
coil is lossless and its size is insignificant in terms of wavelength.

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.

Roy Lewallen, W7EL

Jack Smith wrote:
On Mon, 10 Nov 2003 00:50:55 -0800, Roy Lewallen
wrote:


Ok. So far, we have your calculation that the output current should be
5% smaller, and 18 degrees shifted in phase (lagging, I presume) from
the input; and Cecil's, that the output current should equal the
current, both in phase and magnitude. I don't know if Richard is going
to do the calculation or not, so I'll wait a little longer. Anyone else
like to hazard a prediction?

Roy Lewallen, W7EL


(1) Input current = output current
(2) No phase shift.

If you model the circuit using the lumped values for the antenna R and
jX components it's easy to see this.

Anyone not believing this can try modeling the base inductor as:
O----[0.3 ohms R']--[+j192 ohms]---[0.3 ohms R'']----0
Put current through it using your favorite SPICE simulator and compare
the current through the R' and the R''. The two plots coincide.





Jack K8ZOA

Jack Smith wrote in message . ..
On Mon, 10 Nov 2003 00:50:55 -0800, Roy Lewallen
wrote:

Ok. So far, we have your calculation that the output current should be
5% smaller, and 18 degrees shifted in phase (lagging, I presume) from
the input; and Cecil's, that the output current should equal the
current, both in phase and magnitude. I don't know if Richard is going
to do the calculation or not, so I'll wait a little longer. Anyone else
like to hazard a prediction?

Roy Lewallen, W7EL

(1) Input current = output current
(2) No phase shift.

If you model the circuit using the lumped values for the antenna R and
jX components it's easy to see this.

Anyone not believing this can try modeling the base inductor as:
O----[0.3 ohms R']--[+j192 ohms]---[0.3 ohms R'']----0
Put current through it using your favorite SPICE simulator and compare
the current through the R' and the R''. The two plots coincide.


Very good Jack,
Now use your skills on a inductance that is NOT
a lumped load, and don't forget its orientation so that any
coupling to ground shows up since the subject of discussion
is a loaded whip antenna.
Ofcourse if you have a pure lumped load
kindly take it to the lab for measurement purposes.
Not sure if it will be too heavy now that you have removed
the resistance , capacitance and non current carrying parts
so keep a wheel barrow at hand. grin
Art




Jack K8ZOA