Cecil Moore wrote:
Note that at the frequency where the dipole is 1/2WL and resonant,
it is 180 feet long and 180 degrees long so the number of feet of
wire is also the number of degrees of antenna. Here is my 1/2WL
dipole with current pickup coils installed at points 'x' and 'y' and
FP is the feedpoint,the impedance of which is 60 ohms.

------------------------------FP-------x---------------y-------

Total length is 180 feet. The distance between 'x' and 'y' is 45 feet.
Since feet = degrees in this case, the number of degrees between
'x' and 'y' is known to be 45 degrees from antenna theory. Those
45 degrees are what I am going to attempt to replace with a coil.

So I adjust the feedpoint current to one amp at a reference phase
angle of zero degrees and measure the current at 'x' and the current
at 'y'. The current at 'x' is 0.92 amp at 0 deg. The current at 'y' is
0.38 amp at 0 deg. Already I am not understanding my measurements.

Your measurements are probably wrong.

When did you measure that? After we resolve the error in current, we
can move on.

73 Tom

wrote:
Your measurements are probably wrong.

Not much accuracy is needed to measure a constant phase of zero.
Anyone is invited to duplicate those phase measurements.

When did you measure that? After we resolve the error in current, we
can move on.

I rigged up a 6m dipole yesterday with current pickups driving equal
lengths of coax. Remember, we are not discussing the accuracy of
my magnitude measurements, only of my phase measurements.

After we resolve exactly who made the measurement error, we can
move on. My measurements agree with Figure 14-4 in Kraus'
"Antennas for All Applications", 3rd edition.

Question: would it be legal for me to scan that graphic and post it
on my web page if I give Kraus full credit?
--
73, Cecil, W5DXP

Cecil Moore wrote:

I rigged up a 6m dipole yesterday with current pickups driving equal
lengths of coax. Remember, we are not discussing the accuracy of
my magnitude measurements, only of my phase measurements.

What was the indicator? What was the coupling device?

On six meters, it would take a darned small probe and indicator to not
greatly perturb the system.

If I was going to test something like this, I'd use a small indicator
hanging from the antenna and do it on a low frequency.

So, tell us about the probe and indicator.

73 Tom

wrote

Cecil Moore wrote:
I rigged up a 6m dipole yesterday with current pickups driving equal
lengths of coax. Remember, we are not discussing the accuracy of
my magnitude measurements, only of my phase measurements.

What was the indicator? What was the coupling device?

I have an assortment of toroids of various materials from Amidon. I'm
at work right now and I don't remember if I used 43 or F material.

On six meters, it would take a darned small probe and indicator to not
greatly perturb the system.

They are small toroids. I chose 6m because the dipole area was
physically small.

If I was going to test something like this, I'd use a small indicator
hanging from the antenna and do it on a low frequency.

Please feel free to make that measurement. W7EL just reported that
EZNEC agrees with my phase measurements. So does Kraus.

So, tell us about the probe and indicator.

Similar to the ones W7EL used. They were calibrated within one turn
of each other. The signals at the ends of the coax lines were calibrated
for equality in magnitude and phase. Magnitudes are a relative measurement
but phase was not. I ran the experiment two ways.

One was Lissajous figures on my 100 MHz Leader. The other was putting
the two samples in opposite phase to each other, i.e. phasor subtraction.
For small angles, the angle is equal to the sine of the angle so the
addition
of two coherent sine waves yields an amplitude proportional to the phase
difference when the phase difference is small. The phase difference was
so small it was virtually undetectable.
--
73, Cecil, W5DXP

Cecil Moore wrote:
What was the indicator? What was the coupling device?

I have an assortment of toroids of various materials from Amidon. I'm
at work right now and I don't remember if I used 43 or F material.

How did you construct the coupling transformer? How did you make it
immune to electric fields?

On six meters, it would take a darned small probe and indicator to not
greatly perturb the system.

They are small toroids. I chose 6m because the dipole area was
physically small.

They may be small toroids, but what do they connect to? What is the
common mode impedance of the indicator at 50MHz?

If I was going to test something like this, I'd use a small indicator
hanging from the antenna and do it on a low frequency.

Please feel free to make that measurement. W7EL just reported that
EZNEC agrees with my phase measurements. So does Kraus.

You may not have been measuring anything like you think, in particular
voltage. Just because EZnec agrees with the phase measurements it
doesn't mean the current measurement was even remotely close to being
correct.

So, tell us about the probe and indicator.

Similar to the ones W7EL used. They were calibrated within one turn
of each other. The signals at the ends of the coax lines were calibrated
for equality in magnitude and phase. Magnitudes are a relative measurement
but phase was not. I ran the experiment two ways.

I you hung coaxial lines off a current transformer on a 6-meter dipole
down to some test instrument, you wasted a lot of time. There isn't any
possible way you measured an unperturbed system.

You'd better reconfigure as a monopole, and do it on a lower frequency.


One was Lissajous figures on my 100 MHz Leader. The other was putting
the two samples in opposite phase to each other, i.e. phasor subtraction.
For small angles, the angle is equal to the sine of the angle so the
addition
of two coherent sine waves yields an amplitude proportional to the phase
difference when the phase difference is small. The phase difference was
so small it was virtually undetectable.

I wouldn't trust that system at all.

Even with the equipment I have and having build hunderds of sampling
systems, I'd never attempt a measurement like you just made.

You brought a pair of long coaxial lines that are grounded at the far
end up to within an inch of the antenna, hung what amounts to being a
capacitor between the high voltage high impedance side of the antenna
to ground, and presumed to measure voltage and current on six meters!

You can get away with a toroid on 80 or 40 meters if the test gear and
lines are all near ground potential along with the point of the antenna
you are measuring, but it is really off the wall to assume you can hang
a toroid on a dipole past a loading coil, have that toroid connect to a
cable hanging in air down to some test gear, and not severely perturb
the system. Worse yet, the test was done on 50MHz!

I used a very small floating probe with NO earth path and the indicator
right on the probe. I had to do that to not perturb the system on 40
and 80 meters. I can't imagine trying to do what I did on six meters,
I'd have needed an entire metering system the size of a half-dollar or
smaller.

Making a measurement at the base of a vertical on a low frequency like
Roy did allows the person making the measurement to get away with lots
of things, but I can tell you right now I'd NEVER be able to measure
anything in a short mobile antenna if I ran cables up to the probes, in
particular if I made the test on six meters!

73 Tom

wrote:
Just because EZnec agrees with the phase measurements it
doesn't mean the current measurement was even remotely
close to being correct.

I officially withdraw my measurements as evidence in this
debate and instead substitute the EZNEC results, provided
by W7EL, as evidence.

What does it mean that EZNEC agrees with my possibly
flawed phase measurements? What does it mean that EZNEC
agrees with my argument and disagrees with yours?

How does one use a signal with unchanging phase to measure
the phase shift through a coil or wire? Forgive me if I'm
wrong, but seems to me, you have claimed to have done
exactly that. Please explain how you did that so we can
judge whether your measurements were also flawed.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
I officially withdraw my measurements as evidence in this
debate and instead substitute the EZNEC results, provided
by W7EL, as evidence.

What does it mean that EZNEC agrees with my possibly
flawed phase measurements? What does it mean that EZNEC
agrees with my argument and disagrees with yours?

How does one use a signal with unchanging phase to measure
the phase shift through a coil or wire? Forgive me if I'm
wrong, but seems to me, you have claimed to have done
exactly that. Please explain how you did that so we can
judge whether your measurements were also flawed.


I expected you would want to discuss the problems of making a
measurement in the high impedance part of an antenna with a toroid
around the wire and a coaxial cable running down to a 100MHz scope on
50Mhz.

I see now you really only want to spew, and have no desire to learn
anything.

I took the time to carefully outline what Roy's measurements and mine
would be significantly more reliable, and I see you disregarded that
also.

I'm very disappointed in your reaction to the effort I made to help you
understand measurement techniques.

73 Tom

Cecil Moore wrote:
wrote:

Just because EZnec agrees with the phase measurements it
doesn't mean the current measurement was even remotely

close to being correct.

I officially withdraw my measurements as evidence in this
debate and instead substitute the EZNEC results, provided
by W7EL, as evidence.

What does it mean that EZNEC agrees with my possibly
flawed phase measurements? What does it mean that EZNEC
agrees with my argument and disagrees with yours?

How does one use a signal with unchanging phase to measure
the phase shift through a coil or wire? Forgive me if I'm
wrong, but seems to me, you have claimed to have done
exactly that. Please explain how you did that so we can
judge whether your measurements were also flawed.

Doesn't the change in distance between a pair of current nodes (or
voltage nodes) in the standing wave pattern on a straight conductor
that straddle an inserted inductor show its effective electrical
length? I would think that as long as a fairly pure standing wave
could be arranged with the inductor inside it, this method would allow
the effective electrical length to be measured at arbitrary
frequencies that are not at all related to the coil's self resonant
frequency. It seems that this is nearly what you are demonstrating
with your EZNEC examples. Electrical length (propagation distance) is
collapsing into the inductor.

wrote:
Cecil Moore wrote:
Note that at the frequency where the dipole is 1/2WL and resonant,
it is 180 feet long and 180 degrees long so the number of feet of
wire is also the number of degrees of antenna. Here is my 1/2WL
dipole with current pickup coils installed at points 'x' and 'y' and
FP is the feedpoint,the impedance of which is 60 ohms.

------------------------------FP-------x---------------y-------

Total length is 180 feet. The distance between 'x' and 'y' is 45 feet.
Since feet = degrees in this case, the number of degrees between
'x' and 'y' is known to be 45 degrees from antenna theory. Those
45 degrees are what I am going to attempt to replace with a coil.

So I adjust the feedpoint current to one amp at a reference phase
angle of zero degrees and measure the current at 'x' and the current
at 'y'. The current at 'x' is 0.92 amp at 0 deg. The current at 'y' is
0.38 amp at 0 deg. Already I am not understanding my measurements.

Your measurements are probably wrong.

When did you measure that? After we resolve the error in current, we
can move on.

The measurement looks good to me. The phase is exactly what EZNEC
predicts -- constant along the wire. The ratio in magnitudes we'd expect
depends on the positions along the wire, not just the spacing.

Roy Lewallen, W7EL

"Roy Lewallen" wrote:
The measurement looks good to me. The phase is exactly what EZNEC
predicts -- constant along the wire. The ratio in magnitudes we'd expect
depends on the positions along the wire, not just the spacing.

We are not talking about the magnitude measurements right now.
We are talking about the phase measurements. What good does
it do to use a signal, whose phase is fixed, to measure the phase
shift through a coil or through a wire.

The phase is constant along the wire with or without the presence
of a coil. Why then is a phase shift of zero on both sides of the
coil surprising? And of what importance is that measurement?
--
73, Cecil, W5DXP