Loading Coils; was : Vincent antenna
 

K7ITM wrote:


OK, that leaves us with a difference of opinion, or a difference in
what we are describing. There was an article in "RF Design" maybe 15
years ago now by John Mezak, K2RDX, describing a helical transmission
line model for coils. At the time, he offered free software to
execute the calculations (which also, to me, offered a very practical
way to calculate coil parameters like inductance, effective shunt
capacitance, and first parallel and series self resonances). He later
charged a nominal fee for an improved version of the software, which I
have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound
with 15AWG copper wire, using John's program, I see a variation of
about 2:1 in propagation velocity between 1MHz and 20MHz. Since the
first parallel self-resonant frequency is predicted to be around 8MHz,
it's perhaps not fair to look as high as 20MHz, but even between 1MHz
and 4MHz, I see about 25% change in predicted propagation velocity.

You may say that perhaps John messed all that up terribly, but I don't
think so...and there are other places you can find similar results.
There's an excellent inductance calculator on-line at
http://hamwaves.com/antennas/inductance.html, and though the absolute
value of its prediction of propagation velocity is about 5% different
than Mezak's, they both show very nearly the same percentage change
with frequency.

It might be worth having a bit closer look at, Jim. Perhaps it's just
that you're thinking of a different effect than what these two
programs (and the theory behind them) are modelling.

Cheers,
Tom

Hi Tom -

I suspect that for a given coil, depending on construction, L and/or C
may vary enough over several ocataves to resolve any apparent
'dispute' between my comments and the results provided by Mr. Mezak's
modelling program. I do not believe these effects are large enough to
be responsible for the differences being reported in phenomenon under
discussion.

I would be interested in knowing the results your program produces for
the 100 turn, 2" diameter, 10" long coil that Cecil is concerned
about, if you wouldn't mind sharing them.

Thanks and 73,

Jim, AC6XG

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
With this in mind, you might enjoy how gaming the group is played out
by the more frequent poster(s) insisting on polluting the topic of
directivity with the "electrical" length. The entertainment factor
has been zested up recently by adding the term "equilibrium."

Richard, check out my posting on a stub that is 45
degrees in physical length but performs like a
1/4WL stub. The "electrical" length has to do
with its performance, not its physical length.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

K7ITM wrote:
For the "100 turn, 10 inch long, 2 inch diameter" coil wound
with 15AWG copper wire, using John's program, I see a variation of
about 2:1 in propagation velocity between 1MHz and 20MHz.

Now the question becomes, what was that propagation
velocity at 4 MHz? An EXCEL program that I have gives
a VF of around 0.03 for that coil making a 3 ns delay
through it impossible at 4 MHz.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

On Nov 30, 12:48 pm, art wrote:
On 30 Nov, 12:25, K7ITM wrote:



On Nov 30, 10:59 am, Jim Kelley wrote:

K7ITM wrote:
On Nov 29, 9:11 am, Jim Kelley wrote:
...

Over the range of a few octaves, propagation delay on the other hand
does not vary to any significant extent as a function of frequency.
Ostensibly, it should be equal to sqrt(LC) series L, shunt C.

Actually, Jim, I do expect it to have considerable frequency
dependence. I think you can find info about this in books that
address the design of travelling-wave tubes.

I can't think of an example of an active (or reactive) device which
doesn't have frequency dependent characteristics. To the extent that
indices of refraction are frequency dependent, propagation velocity
does in fact vary with frequency. If it didn't, we wouldn't see
rainbows. Dielectric constants do indeed have a frequency dependence.
But to first order, at radio frequencies, in amateur applications,
for the purposes of this discussion, and in my opinion, the effect is
less than considerable - particularly if we assume the L and C in
sqrt(LC) are correct at the frequency of interest. ;-)

73, Jim AC6XG

OK, that leaves us with a difference of opinion, or a difference in
what we are describing. There was an article in "RF Design" maybe 15
years ago now by John Mezak, K2RDX, describing a helical transmission
line model for coils. At the time, he offered free software to
execute the calculations (which also, to me, offered a very practical
way to calculate coil parameters like inductance, effective shunt
capacitance, and first parallel and series self resonances). He later
charged a nominal fee for an improved version of the software, which I
have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound
with 15AWG copper wire, using John's program, I see a variation of
about 2:1 in propagation velocity between 1MHz and 20MHz. Since the
first parallel self-resonant frequency is predicted to be around 8MHz,
it's perhaps not fair to look as high as 20MHz, but even between 1MHz
and 4MHz, I see about 25% change in predicted propagation velocity.

You may say that perhaps John messed all that up terribly, but I don't
think so...and there are other places you can find similar results.
There's an excellent inductance calculator on-line athttp://hamwaves.com/antennas/inductance.html, and though the absolute
value of its prediction of propagation velocity is about 5% different
than Mezak's, they both show very nearly the same percentage change
with frequency.

It might be worth having a bit closer look at, Jim. Perhaps it's just
that you're thinking of a different effect than what these two
programs (and the theory behind them) are modelling.

Cheers,
Tom- Hide quoted text -

- Show quoted text -

Where can I obtain a copy of Johns program?
TIA
Art

You might start by asking John. I'm sure he's in the QRZ database.

Cheers,
Tom

Loading Coils; was : Vincent antenna
 

Jimmie D wrote:
"Tom Donaly" wrote in message
t...
Cecil Moore wrote:
Tom Donaly wrote:
And, if the total electrical length isn't 90 degrees, you
add a few degrees to the loading coil to make it come out right.
Very ingenious.
Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.
Suuurrrre it is. You've got 90 degrees on the brain, Cecil.
Next, you'll be talking about 90 degree equilibrium.
73,
Tom Donaly, KA6RUH

I must be wrong too which doesnt surprise me.

Are you saying that if I put a center loaded antenna on my trucks tool box,
tune it to reonance at some freqency then the antenna is not electrically 90
degrees or some integer mutilple of 90 degrees in length at that frequency.

The concept that a resonant antenna could be some other electrical length is
something new to me as I thought this was the defintion of resonance being
equivalent to saying the feedpoint impedance is non reactive.

Jimmie



Slap it on your truck, and tell us at what frequencies it resonates.
Can you get it to resonate at odd multiples of its fundamental frequency?
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

On Nov 30, 1:03 pm, Jim Kelley wrote:
K7ITM wrote:
OK, that leaves us with a difference of opinion, or a difference in
what we are describing. There was an article in "RF Design" maybe 15
years ago now by John Mezak, K2RDX, describing a helical transmission
line model for coils. At the time, he offered free software to
execute the calculations (which also, to me, offered a very practical
way to calculate coil parameters like inductance, effective shunt
capacitance, and first parallel and series self resonances). He later
charged a nominal fee for an improved version of the software, which I
have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound
with 15AWG copper wire, using John's program, I see a variation of
about 2:1 in propagation velocity between 1MHz and 20MHz. Since the
first parallel self-resonant frequency is predicted to be around 8MHz,
it's perhaps not fair to look as high as 20MHz, but even between 1MHz
and 4MHz, I see about 25% change in predicted propagation velocity.
You may say that perhaps John messed all that up terribly, but I don't
think so...and there are other places you can find similar results.
There's an excellent inductance calculator on-line at
http://hamwaves.com/antennas/inductance.html, and though the absolute
value of its prediction of propagation velocity is about 5% different
than Mezak's, they both show very nearly the same percentage change
with frequency.

It might be worth having a bit closer look at, Jim. Perhaps it's just
that you're thinking of a different effect than what these two
programs (and the theory behind them) are modelling.

Cheers,
Tom

Hi Tom -

I suspect that for a given coil, depending on construction, L and/or C
may vary enough over several ocataves to resolve any apparent
'dispute' between my comments and the results provided by Mr. Mezak's
modelling program. I do not believe these effects are large enough to
be responsible for the differences being reported in phenomenon under
discussion.

I would be interested in knowing the results your program produces for
the 100 turn, 2" diameter, 10" long coil that Cecil is concerned
about, if you wouldn't mind sharing them.

Thanks and 73,

Jim, AC6XG

Hi Jim,

Just go to the website I provided a link for. The results of the
calcs it performs are certainly within typical experimental tolerance
of the results from Mezak's program. But it's just one model, and you
MUST understand the model and what it's trying to accomplish if you're
going to be successful in applying it.

As for the effects being "large enough to be responsible for...," I
think you will find that the explanation there is adequately covered
by people thinking they understand what someone else has described,
and thinking it's at odds with what they have observed, or with their
own theory (which may or may not be flawed in itself). Like I wrote
before, I'm really not much interested in getting mired down in that
same old stuff (once again). I'm having way too much fun actually
building things with coils (and other parts) and getting them to
perform useful functions. I've learned FAR more about coils and the
circuits they're used in over the past year from designing and
building circuits than I have from looking at the same old stuff here
on r.r.a.a. that's never going to get resolved because someone has too
much invested in wanting to be "right."

Cheers,
Tom

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:

...
Note that the electrical length and the physical length
are nowhere near the same value. The electrical length
can be 90 degrees at resonance while the physical length
is only 13 degrees for a 75m mobile antenna.
...

I have been thinking on this. From past posts, I think some think that
a 1/4 wave monopole and a 1/2 wave electrical length monopole shortened
to 1/4 physical length have very similar launch/radiation
characteristics... if they do, then it is obvious that their modeling
program is "BLOWING SMOKE!"

A 90 degree shift in 1/4 wave physical space will never duplicate a 180
shift in the same physical dimensions!

Regards,
JS

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:


W8JI measured a 4.5 degree phase shift in the
standing-wave current being used for the
measurement although virtually no phase
information exists in the standing-wave current
phase. W7EL made exactly the same mistake in
his measurements. No wonder the two agree.

Cecil,

I have stared at the W8JI web page

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

for a long time, and I just cannot find anyplace where he mentions 4.5
degrees. Is that your calculation rather than Tom's?

The graphic appears to be a screen shot from a network analyzer. W8JI
does not describe it any further on that page, but it may be an HP
8753D, based on information elsewhere on his site.

In any case the plot appears to be S21 "delay" vs. frequency. I do not
know anything about that instrument, but this appears to be an
appropriate choice for the question at hand. There are two markers
active. Marker 1 shows 3.0361 ns at 3.825 MHz. Marker 2 shows 486.43 ns
at 16.11525 MHz. Marker 1 presumably represents a typical 80 m
frequency. Marker 2 is at a peak in the graph, and it appears to mark a
resonance.

Sooooo, the questions a

* Who made the mistake?
* Does the HP network analyzer system not work correctly?
* Do you think the HP engineers were not aware of standing waves?
* Did Tom make the hook-up incorrectly?
* Is there some other calibration factor needed? (Perhaps the Corum
factor or the Cecil factor was omitted.)
* Did the analyzer place the decimal point in the wrong spot?
* Is "new math" needed? Does 3.0361 ns really equal 30 ns in some other
coordinate system?

Inquiring minds want to know.

8-)

73,
Gene
W4SZ

tesla coils antennas maxwell Loading Coils; was : Vincent antenna
 

"AI4QJ" wrote in message
...

"art" wrote in message
...
On 30 Nov, 11:01, Jim Lux wrote:
Tom,
May I point out that a Tesla coil is an "antenna" that does not
conform
to Maxwells laws with respect to the adherance to the LC ratio.
The LC ratio is out of balance such that the capacitor is not
of the correct size to store and then return the imposed energy from
the inductive heavy coil which is visually seen as resulting in a
spark.
Regards
Art

Huh...

tesla coils follow all of Maxwells equations quite nicely. Paul
Nicholson did some very nice analysis on this a few years back,
published at a link previously posted.

They're two coupled LC resonant circuits, with the coupling adjusted to
around k=0.2. There are higher order systems with 3 or more resonators,
as well (called Magnifiers in the TC world)

The challenge in spark making is choosing appropriate operating
parameters (coupling, radius of curvature, topload capacitance, etc.) to
optimally promote spark growth.

Let me make it quite clear. I was referring to a single coil and
not the feeding arrangement. I used that as a refernce only in
conjunction
with the subject of antenna coils. This single coil, tho resonant,
does
not meet the requirements that Maxwell demands ie equilibrium.
Further study of that coil will show the effect of ground beyond the
coil
which thus involves the system as well as the associated coil for feed
coupling.
Regards
Art Unwin..KB9MZ....xg

But you made the straightforward statement: "Tesla coils do not conform to
Maxwell's laws", thus opening the door to a new field of study in
Electromagnetics. In fact, if you could look into this a little deeper,
you may in fact be the first person to unify field theory (something
Albert Einstein himself failed to do). This may be related to the success
of the Philadelphia Experiment.
I think you are on to something here :-)

That would appear to be a partial quote from the sentence and implies a
completely different meaning from what was stated. I interpreted the
statement to mean that Tesla coils exhibit extreme LC ratios which are
outside the ranges that have been found to be most efficient in resonant
circuits for radio communication. (As established by Maxwell and others from
experimentation.)

A resonant circuit for any given frequency can be made up using a capacitor
and inductance of any suitable values. Using very a very large capacitor and
a small inductor, or a large inductor and small capacitance may well work
very well in a given situation, but experience has shown that selecting
components with median values results in more stable and efficient circuit
operation.

Tesla coils form very sharply tuned circuits with some quite extreme
component values and voltage levels. Their operating parameters do tend to
lie outside what is considered 'normal' for amateur radio.

The Philadelphia Experiment was a success? Why didn't anybody tell me? What
time did the ship get back?

Mike G0ULI

Loading Coils; was : Vincent antenna
 

"AI4QJ" wrote in
:

....

Calculates DC resistance of wi

Now, 18 AWG wire is .00751 Ohms/foot. At 53 feet,

R(L) = 0.398 Ohms


And proceeds to use DC resistance of wire to analyse performance at RF:

Phase angle: tan(theta) = 3600/0.398 = 9045