On Sat, 18 Mar 2006 19:57:32 GMT, Cecil Moore
wrote:

Reg Edwards wrote:
- - - and I get the impression nobody learned anything!

You think nobody learned anything from the fact that
measuring standing wave current phase is meaningless?
If nobody learned anything, they would no doubt still
be contributing to the technical discussion.

Here's what I think happened. Person A and Person B
engage in an argument and both are wrong. Person A
believes he cannot possibly be wrong so he digs in and
argues his rigid position. Person B realizes that he may
be wrong and uses the scientific method to fine tune his
argument thus correcting any errors along the way.

Which person has the advantage and is likely to win
the argument?


I tried learning something. I didn't get to read the whole thread so
may have missed the important part?

When the measurements of the coil were done on the bench it seems that
it was done with 50 ohms in and 50 ohms out. That hardly seems like it
would give the same information as when the coil was in actual use as
an antenna loading coil.

Rather than a 50 ohm load how about if a load was placed at the end of
the coil to simulate the antenna, a resistor and capacitor to take the
place of the antenna impedance and reactance. Then measure the current
in and out and the phase shift.

73
Gary K4FMX

Gary Schafer wrote:
Rather than a 50 ohm load how about if a load was placed at the end of
the coil to simulate the antenna, a resistor and capacitor to take the
place of the antenna impedance and reactance. Then measure the current
in and out and the phase shift.

The measurement problem is harder than it looks. Here's
a quote from "Field and Waves in Modern Radio", Ramo and
Whinnery, 2nd edition, page 227.

"Difficulties in applying these equations arise since
the current and charge distributions are not known, but
are determined by the field distributions which are
calculated from the retarded potentials which depend
upon current and charge distribution - a vicious circle!
The exact solution of this problem is usually of
prohibitive difficulty."
--
73, Cecil http://www.qsl.net/w5dxp

Gary Schafer wrote:

When the measurements of the coil were done on the bench it seems that
it was done with 50 ohms in and 50 ohms out. That hardly seems like it
would give the same information as when the coil was in actual use as
an antenna loading coil.

A bench test is fine. An inductor is an inductor.

The only problem with a bench test is simulating the load impedance
presented by the antenna and of course strong local fields generated
by the antenna are missing, but the actual error can be reasonably
small.

However, inductors were measured in an actual antenna. I measured
current, and Roy Lewallen measured phase and current.

I couldn't measure time delay or phase in my actual antenna because I
was measuring a mobile antenna. There wasn't any way to measure phase
without perturbing the system and rendering any data unreliable.

This long painful thread (it's been going on years now) started because
K3BU claimed a loading inductor had most of the current in the first
few turns. I made some measurements
and posted them at:

http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

These measurements show exactly what anyone who understands loading
coils would expect, that it is stray C in comparison to load impedance
on the inductor that determines any current taper, and that for a
reasonable sized inductor the taper is very small.

I wrote a description at:

http://www.w8ji.com/mobile_and_loaded_antenna.htm

I can't see anything in there that needs changed, based on what I've
read here in this thread.

Rather than a 50 ohm load how about if a load was placed at the end of
the coil to simulate the antenna, a resistor and capacitor to take the
place of the antenna impedance and reactance. Then measure the current
in and out and the phase shift.

I've done that also.

You are absolutely correct Gary, it is possible to come very close with
a lumped load on the inductor *except* of course the surroundings are
different.

The inductor test fixture I normally use is a large copper box made
from blank double sided PC board sheets. It has vacuum caps (very high
Q) and various detectors and probes.

I have to characterize large inductors on occasion as part of designing
RF systems. It's less scary than turning on a 50kW PA and having things
misbehave at full power, or building a phasing system or phasing/ATU
combo that doesn't work.

73 Tom

wrote:
************************************************** **************
Please turn your technical expertise on this example which I
have asked you about many times with no response from you:

http://www.qsl.net/w5dxp/current.htm

At the bottom of the page, the coil is seen to have 0.17 amps
at the bottom and 2.0 amps at the top. With your lumped inductor
way of thinking, how is that possible?
************************************************** ***************
A bench test is fine. An inductor is an inductor.

But the chosen valid model varies depending upon which inductor
it is. Dr. Corum says the model must be changed over at 15 degrees
of the self-resonant frequency. These are velocity inhibited slow-
wave helical coils that we are talking about.

And standing wave current is certainly not traveling wave
current. Remember what Gene Fuller said? Please read it again.

Gene said about standing wave current:
Phase is gone. Kaput. Vanished. Cannot be recovered.
Never to be seen again. The only "phase" remaining is the
cos (kz) term, which is really an amplitude description,
not a phase.

How can one use a signal where the phase is gone to measure phase?

However, inductors were measured in an actual antenna. I measured
current, and Roy Lewallen measured phase and current.

You and Roy measured standing wave current the phase of which is
unchanging over the coil and whip and entire antenna. You should
have realized over the past week that those measurements were
meaningless. EZNEC shows the same thing. Kraus reports the same
thing.

ONE CANNOT USE THE PHASE OF STANDING WAVE CURRENT TO MEASURE THE
PART OF AN ANTENNA THAT A LOADING COIL REPLACES.

... and that for a
reasonable sized inductor the taper is very small.

The present argument is not about taper, it is about how much of
a wavelength a loading coil occupies. One cannot measure that value
using standing wave current as you and Roy did. Roy reported
accurate phase measurements but standing wave current phase is
meaningless since it has unchanging phase.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
Please turn your technical expertise on this example which I
have asked you about many times with no response from you:

http://www.qsl.net/w5dxp/current.htm

At the bottom of the page, the coil is seen to have 0.17 amps
at the bottom and 2.0 amps at the top. With your lumped inductor
way of thinking, how is that possible?

Yes it is possible. There is no difference between doing things as
lumped components or standing wave models.

The only disagreement is you seem to claim some very odd things about
current not flowing, unless in the course of 400 posts you have
corrected that.

This entire thread reminds me of the Fractenna threads of years ago.

73 Tom

wrote:
. . .
This entire thread reminds me of the Fractenna threads of years ago.

Don't be so harsh, Tom. Cecil hasn't threatened to sue anybody or called
anyone a pirate. But I have to say that the logic does have a familiar ring.

Roy Lewallen, W7EL

wrote:

Cecil Moore wrote:
At the bottom of the page, the coil is seen to have 0.17 amps
at the bottom and 2.0 amps at the top. With your lumped inductor
way of thinking, how is that possible?

Yes it is possible. There is no difference between doing things as
lumped components or standing wave models.

Please explain how 0.17 amps can be on the source side of a
lumped inductor while 2.0 amps exists at the top of the
inductor.
--
73, Cecil http://www.qsl.net/w5dxp

wrote

This long painful thread (it's been going on years now) started because
K3BU claimed a loading inductor had most of the current in the first
few turns.

I am back after loooong absence here and see more misinformation coming from
Tom, W8JI.

I claimed that current in the antenna coil is NOT CONSTANT (or near) as he
claimed.
The case was of electrical quarter wave vertical radiator (as loaded mobile
antenna) and that the current is distributed, varying across the coil as I
have experienced, W9UCW has measured and Cecil has explained.
The refresher is at
http://www.k3bu.us/loadingcoils.htm

The thread is "painful" because some people try to subvert the reality and
keep clinging to wrong "reality" and some try to set the record straight..
This misinformation keeps being perpetuated in literature and it even crept
into the latest ON4UN 4th edition of Low Band DXing (see page 9-33).

The significance of properly realizing the current distribution in the
loading coil is in how the modeling programs treat the phenomena and major
screw-up will show up in multi element loaded antenna systems, where error
will multiply and give false results.
There are few more statements slightly out of true on W8JI pages, but would
have to be left for later time.

I apologize for being away from this NG, my AOL provider dumped NG and I am
slowly dumping AOL and will migrate to optonline.net and back to NG. Also
business and other QRM keeps me away, but I hope is that "tings" will
improve.

73 to all
Yuri, K3BU
www.K3BU.us
www.TeslaRadio.org

Yuri Blanarovich wrote:
wrote

This long painful thread (it's been going on years now) started because
K3BU claimed a loading inductor had most of the current in the first
few turns.

I am back after loooong absence here and see more misinformation coming from
Tom, W8JI.

I claimed that current in the antenna coil is NOT CONSTANT (or near) as he
claimed.
The case was of electrical quarter wave vertical radiator (as loaded mobile
antenna) and that the current is distributed, varying across the coil as I
have experienced, W9UCW has measured and Cecil has explained.

Yuri,

Why don't you explain in a few words how you think the loading coil
works?

Also, why do you think a mobile antenna is "90 degrees long" when it
has a loading coil?

The loading coil, if well-designed and of compact size, doesn't have to
have any significant current taper. The exception would be if the
antenna above the coil has small capacitance compared to distributed
capacitance from the coil to space or to ground.

Do you still disagree with this?

73 Tom

wrote:
The loading coil, if well-designed and of compact size, doesn't have to
have any significant current taper.

The current taper depends upon where the coil is installed in
the standing wave environment. There is no doubt that the coil
distorts the current away from the ideal thin-wire dipole case.
But that coil does have to have a significant delay, in the tens
of degrees according to Dr. Corum. Since you and Roy mistakenly
used standing wave current phase to try to measure the delay
through a coil, the following posting resulted:

Gene Fuller, W4SZ wrote:
In a standing wave antenna problem, such as the one you describe, there is no
remaining phase information. Any specific phase characteristics of the traveling
waves died out when the startup transients died out.

Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again.

The only "phase" remaining is the cos (kz) term, which is really an amplitude
description, not a phase.

Gene is 100% correct and we all should be grateful for that posting.

Neither you nor Roy have ever made a valid measurement of the
delay through a coil. It is admittedly a difficult measurement
to make directly. Ramo and Whinnery say it "is usually of
prohibitive difficulty".
--
73, Cecil http://www.qsl.net/w5dxp