Current through coils
 

Cecil Moore wrote:
Richard Clark wrote:

Provide the Velocity Factor and Characteristic Impedance per the
formulas you offered:


Tom Donaly has graciously volunteered to provide those values.
Please stand by.

Actually, I just wanted to calculate the values for my own personal
edification. You'll have to do the arithmetic yourself, Cecil, and
then it won't mean much, because, as far as I know, no one has ever
done any experimental work to see if these equations have any meaning.
If a coil can slow down an electromagnetic wave as much as these
equations say it can, though, it qualifies as a very interesting device.
73
Tom Donaly, KA6RUH

Current through coils
 

Tom Donaly wrote:
If a coil can slow down an electromagnetic wave as much as these
equations say it can, though, it qualifies as a very interesting device.

Tom,

Here's another way to think about it.

If an inductor by itself delayed phase as much as Cecil claims, we
could build a phase or time delay system with only a large inductor. As
it is, we must always use a network of capacitors and inductors to
obtain phase delays or a transmission line of any substantial delay.

To construct a delay line, either a small parallel wire line is used or
a spiral around a metal core. The metal core acts like a shorted turn
and reduces flux coupling, and adds distributed capacitance to ground.

73 Tom

Current through coils
 

On 15 Mar 2006 16:36:51 -0800, wrote:

If an inductor by itself delayed phase as much as Cecil claims, we
could build a phase or time delay system with only a large inductor.

There is another explanation.

A lumped circuit has only one resonance. A transmission line has an
infinite number. It certainly isn't necessary to impose a strict test
of this. Finding second, third, and fourth harmonics for an inductor,
in situ, would certainly be compelling evidence of transmission line
behavior. Otherwise, any delay obtained through pencil whipping the
various formulas (and Reggie's equations veer far from the references
offered) is strictly what occurs AT RESONANCE, and any interpolation
of that delay to other frequencies is a presumption not yet proven.

73's
Richard Clark, KB7QHC

Current through coils
 

On Wed, 15 Mar 2006 15:38:32 -0800, Roy Lewallen
wrote:
Many analog scopes aren't capable of producing a meaningful Lissajous
figure at HF because of the limited bandwidth of the horizontal channel.

This is certainly true for poor scopes. If we are limited to HF, then
those with bandwidths above 100MHz might squeak by. However, there
are alternatives that were part and parcel to many older scopes: you
simply drive the plates directly like they did in the old days (1930s)
before the plates were driven by dedicated amplifier chains.

I have calibrated such old (very old) scopes that operated well out
into the 100s of MHz, but were often accompanied by a necessary
accessory, a microscope.

73's
Richard Clark, KB7QHC

Current through coils
 

On Wed, 15 Mar 2006 22:42:55 GMT, Cecil Moore wrote:
The VF of my 75m bugcatcher coil calculates out to be
VF = 0.0175 at 6.6 MHz

On Fri, 10 Mar 2006 13:35:14 GMT, Cecil Moore wrote:

I'm willing to bet that my 75m
bugcatcher coil has at least a 40 nanosecond delay on 4 MHz
which is a 60 degree current phase shift.

On Wed, 15 Mar 2006 18:03:28 GMT, Cecil Moore wrote:

The coil data is: ~6" dia, ~6.7" long, 26.5 T, seems
very close to 4 TPI. Looks to be #14 solid wire.

Total turns 26.5
Through total turns, total wire appears to be 505"

With nothing offered in the way of inductance, from calculations it
appears to be 72.9 µH

With nothing offered in the way of distributed capacitance, from
calculations it appears to be 8pF

On Tue, 14 Mar 2006 04:09:08 +0000 (UTC), "Reg Edwards"
wrote:
V = 1 / Sqrt( L * C ) metres per second,
where L and C are henrys and farads per metre respectively. The
formula for L and C can be found in your Bibles from coil dimensions,
numbers of turns, etc.

V = 1 / Sqrt (5.88 * 72.9* 10^-6 * 8 * 10^-12) meters per second

where the 5.88 is to correct for per meter computations

it follows that V must then be 17.1 million meters per second


The velocity factor = V / c
Vf = 0.057
and Zo = Sqr( L / C ).
Zo = Sqrt (72.9* 10^-6 / 8 * 10^-12)

3 KOhms

It appears your reference source leads you to an answer that is off by
325%

OR

Reggies' hints of a solution are in error

OR

I've pencil whipped this to death due to the tedious collection of
data spread through 300 postings and the chain of computation. I will
leave that to other, less lazy individuals to ponder.

OR

This is simply proof of an exercise in futility through the
misapplication of the theory of transmission lines to lumped
components.

It is quite apparent something's broke, but if the correspondence
descends into theory, it will be that theory is broke. There's enough
quantifiables to come to terms with before any theory is proven.

Current through coils
 

Richard Clark wrote:
On Wed, 15 Mar 2006 15:38:32 -0800, Roy Lewallen
wrote:
Many analog scopes aren't capable of producing a meaningful Lissajous
figure at HF because of the limited bandwidth of the horizontal channel.

This is certainly true for poor scopes. If we are limited to HF, then
those with bandwidths above 100MHz might squeak by. . .

Either you missed my point, or we differ on what constitutes a "poor"
scope. The Tektronix 465, for example, is a 100 MHz scope. Although it's
very long in the tooth now, it's not a "poor" scope by most measures.
But the specifications for X-Y display are as follows:

------

5 mV/div to 5 V/div, accurate ± 4%. Bandwidth is dc to at least 4 MHz.
Phase difference between amplifiers is 3° or less from dc to 50 kHz.

------

This wouldn't produce a meaningful Lissajous figure at HF.

Roy Lewallen, W7EL

Current through coils
 

Richard Clark wrote:
On Wed, 15 Mar 2006 22:42:55 GMT, Cecil Moore wrote:
The VF of my 75m bugcatcher coil calculates out to be
VF = 0.0175 at 6.6 MHz

On Fri, 10 Mar 2006 13:35:14 GMT, Cecil Moore wrote:

I'm willing to bet that my 75m
bugcatcher coil has at least a 40 nanosecond delay on 4 MHz
which is a 60 degree current phase shift.

On Wed, 15 Mar 2006 18:03:28 GMT, Cecil Moore wrote:

The coil data is: ~6" dia, ~6.7" long, 26.5 T, seems
very close to 4 TPI. Looks to be #14 solid wire.

Total turns 26.5
Through total turns, total wire appears to be 505"

With nothing offered in the way of inductance, from calculations it
appears to be 72.9 µH

With nothing offered in the way of distributed capacitance, from
calculations it appears to be 8pF

On Tue, 14 Mar 2006 04:09:08 +0000 (UTC), "Reg Edwards"
wrote:
V = 1 / Sqrt( L * C ) metres per second,
where L and C are henrys and farads per metre respectively. The
formula for L and C can be found in your Bibles from coil dimensions,
numbers of turns, etc.

V = 1 / Sqrt (5.88 * 72.9* 10^-6 * 8 * 10^-12) meters per second

where the 5.88 is to correct for per meter computations

it follows that V must then be 17.1 million meters per second

The velocity factor = V / c
Vf = 0.057
and Zo = Sqr( L / C ).
Zo = Sqrt (72.9* 10^-6 / 8 * 10^-12)

3 KOhms
. . .

This is a misapplication of transmission line formulas. The "C" in those
formulas is the shunt capacitance per unit length between the
conductors, not a series or longitudinal capacitance as used here. In
order to use the transmission line formulas, you have to have a second
conductor and determine the C per unit length between the two
conductors. Otherwise, you (or Cecil) have to come up with some other
equations. Some of the more picky of us readers will of course then ask
for the source and/or derivation of those other equations.

Roy Lewallen, W7EL

Current through coils
 

Tom Donaly wrote:
Actually, I just wanted to calculate the values for my own personal
edification. You'll have to do the arithmetic yourself, Cecil, and
then it won't mean much, because, as far as I know, no one has ever
done any experimental work to see if these equations have any meaning.

There are references for it in the Dr. Corum IEEE paper.
Kandoian and Sichak, "Wide Frequency Range Tuned Helical
Antennas and Circuits," Electrical Communications, Vol 30,
1953, pp. 294-299. It was published while I was in high
school.

If a coil can slow down an electromagnetic wave as much as these
equations say it can, though, it qualifies as a very interesting device.

I studied such 50 years ago at Texas A&M from papers
such as the above. The parameters for a transmission line
or a coil are the same just with different values.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

wrote:
If an inductor by itself delayed phase as much as Cecil claims, we
could build a phase or time delay system with only a large inductor.

We can build a time delay system with only a large inductor.
That's what large inductors do. How does a large inductor
cause a large arc on a Smith Chart without shifting the phase
of the signal?

One cannot use the presuppositions of the lumped-circuit
model to prove that there is no time delay through a
coil. The lumped-circuit presupposes zero time delay
through a coil with propagation times exceeding the
speed of light.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Richard Clark wrote:
A lumped circuit has only one resonance. A transmission line has an
infinite number. It certainly isn't necessary to impose a strict test
of this. Finding second, third, and fourth harmonics for an inductor,
in situ, would certainly be compelling evidence of transmission line
behavior.

Using the same coil stock as W8JI's 100uH coil, I just set up
a 50 uH coil on a mag mount sitting on my metal desk. Its
first solid resonance was 9 MHz (1/4WL), its second solid
resonance was 27 MHz (3/4WL), and its third solid resonance
was 45 MHz (5/4WL). In addition to those, there other soft
spots and double dips along the frequency line.

W8JI reported something happening at 24 MHz as well as self-
resonance at 16 MHz. He was apparently not testing it over
a ground plane like an automobile body. That automobile
ground plane drops the VF much lower than an isolated
coil's VF.
--
73, Cecil http://www.qsl.net/w5dxp