Current through coils
 

What's the difference between the transmission line model and
the reflection model?
--
73, Cecil
=======================================

No difference whatsoever - except that Cecil is obsessed with
reflections and he worships some guy named Corum. ;o)
----
Reg.

Current through coils
 

On Sun, 26 Mar 2006 18:03:26 GMT, Cecil Moore
wrote:
Don't you know how to turn on the 'Current Phase' option when
displaying EZNEC results. Do you need a tutorial?

This is YOUR work, not mine, thus it is YOUR problem, not mine.

Trying to add those phases shows a lot of ignorance.

Ah! Leading with your chin again.


3. The coil Vf shown on the web is 0.1375 is different than
eq (32) = 0.0078

Sorry, you're wrong. eq(32) for this coil yields a VF of ~0.033

Can't do the math? Twice?

which Dr. Corum claims to be accurate within about 10%.

10% 50% 59%? and now we're down to "pick a number, any number"

4. refuting your own references (Corum²).

Dr. Corum's equation for the coil VF is at its *SELF-RESONANT*
frequency, not anywhere else. Using it anywhere else is only
a *VERY ROUGH* estimate. At the self resonant frequency reported
by EZNEC, the VF calculates out to be ~0.055.

Thank you for making my point.

and the answer remains:
Strange?
No, 4 out of 4 stand as an amusing footnote.

Current through coils
 

On Sun, 26 Mar 2006 18:04:56 GMT, "Tom Donaly"
wrote:

Cecil never actually reads his references

Hi Tom,

The legacy of conducting research by Xerox.

73's
Richard Clark, KB7QHC

Current through coils
 

Reg Edwards wrote:
I'm glad to know that I can substitute a coil of wire every time I
need a transmission line. So tell me, Reg, what
are the specs on the coil I'd need to make a transmission line
transformer to match 75 ohms to 325.33 ohms?
73,
Tom Donaly, KA6RUH

=======================================
Every coil is a transmission line.

But not every transmission line is a coil.
----
Reg.



An answer worthy of a zen master. If you keep this
up, Reg, we'll all be cursed with enlightenment.
73,
Tom Donaly, KA6RUH

Current through coils
 

On Sun, 26 Mar 2006 19:14:36 GMT, Cecil Moore
wrote:

I've said it befo The delay
through the coil is what it is and we don't know exactly what
it is.

Is Popeye Descartes your latest personality?

Current through coils
 

On Sun, 26 Mar 2006 22:16:57 +0100, "Reg Edwards"
wrote:

Every coil is a transmission line.

But not every transmission line is a coil.

Looks like a zen worm has spam infected newsgroupspace.

Current through coils
 

Tom Donaly wrote:

An answer worthy of a zen master. If you keep this
up, Reg, we'll all be cursed with enlightenment.
73,
Tom Donaly, KA6RUH

Funny you should say that. Made me think of the (not really correct)
"zen archery" philosophy of defining the target as being wherever the
arrow strikes. So the arrow always hits the target.

In reading this thread I find that line of reasoning familiar.

Roy Lewallen, W7EL

Current through coils
 

Richard Clark wrote:
Cecil Moore wrote:
Don't you know how to turn on the 'Current Phase' option when
displaying EZNEC results. Do you need a tutorial?

This is YOUR work, not mine, thus it is YOUR problem, not mine.

It's my problem that you don't know how to turn on the
'Current Phase' option in EZNEC??? Just how do you propose
that I gain control over your computer? It states on the
graphic that the 'Current Phase' option is 'ON'.

Trying to add those phases shows a lot of ignorance.

Ah! Leading with your chin again.

If you are really into adding up phase angles, then add
them up every inch. You will approach infinity as the sum.
Your approach is a lot like adding up power every inch
and declaring the transmission lines contains eighteen
gigawatts of power.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

It appears that Cecil is back with many postings, but he seems to be
ignoring answering my question. Perhaps he's unable to do so. Just so
the lurkers understand that indeed it is possible to work through the
phasor math, here goes. Here's exactly the scenario Cecil set up,
quoted from his posting:

==========

"So to be perfectly clear, here is my statement re-worded using
a 45 degree phase shift through the coil.

The forward current magnitude is equal at both ends of the coil.
The reflected current magnitude is equal at both ends of the coil.

At the bottom of the coil, the forward current is 1 amp at zero deg.
At the bottom of the coil, the reflected current is 1 amp at zero deg.
At the bottom of the coil, the standing wave current is 2 amps at
zero deg.

At the top of the coil, the forward current is 1 amp at -45 deg.
At the top of the coil, the reflected current is 1 amp at +45 deg.
At the bottom of the coil, the standing wave current is 1.4 amp at
zero deg."

==========

OK, so the difference in "FORWARD" current from the bottom to the top
is:
fwd.bottom.current - fwd.top.current
= 1A at 0 degrees - 1 amp at -45 degrees
= 1+j0 - sqrt(.5)-j*sqrt(.5)
= 1-sqrt(.5) + j*sqrt(.5)
(about 0.765 at 67.5 degrees)


The difference in "REFLECTED" current from the bottom to the top is:
refl.bottom.current - refl.top.current
= 1A at 0 degrees - 1 amp at +45 degrees
= 1+j0 - sqrt(.5)-j*sqrt(.5)
= 1-sqrt(.5) - j*sqrt(.5)

The SUM of these two differences is:
[1-sqrt(.5) + j*sqrt(.5)] + [1-sqrt(.5) - j*sqrt(.5)]
= 2 - 2*sqrt(.5) + j0
= 2 - sqrt(2) + j0
= 2 - sqrt(2) at zero degrees

The standing wave current at the bottom of the coil is 2 amps just as
Cecil suggests at one point: It's the sum of the "forward" and
"reflected":
net current at the bottom = sw.bottom.current
= 1+j0 + 1+j0
= 2+j0
= 2 at zero degrees

Presumably Cecil meant that the standing wave current at the TOP
(not the BOTTOM) of the coil is 1.4 amps at 0 degrees. That's close,
but more exactly, it's
net current at the top = sw.top.current
= sqrt(.5)-j*sqrt(.5) = sqrt(.5)+j*sqrt(.5)
= 2*sqrt(.5)
= sqrt(2)
= sqrt(2) at zero degrees.

So the difference in net current (that is, the difference in the
standing wave current) between the top and the bottom of the coil
in this example is exactly:

sw.bottom.current - sw.top.current
= 2 at zero degrees - sqrt(2) at zero degrees
= 2 - sqrt(2) at zero degrees

So, we see that the difference in current between the bottom and
the top is exactly the same, independent of whether we just use
the standing-wave currents, or the currents in the "forward"
travelling wave plus the currents in the "reflected" wave. That it's
also
exactly the same answer you get by looking at a full cycle of
instantaneous currents is left as an exercise (fairly simple) for the
reader.

Either way, there is a difference, and that current must go
somewhere. It should be pretty easy to account for it. In
fact, it's not even very hard to predict fairly accurately in
the case of a loading coil in an antenna perpendicular to a ground
plane or equivalently in a symmetrical doublet.

Cheers,
Tom

Current through coils
 

Cecil Moore wrote:
(snip)
Here's what EZNEC reports as the phase shift through the coil
in the traveling wave antenna previously tested at 5.89 MHz.

5.5 MHz: 14.1 deg, 5.89 MHz: 15.7 deg, 6 MHz: 16.2 deg,
7 MHz: 21.4 deg, 8 MHz: 29.5 deg, 9 MHz: 45.9 deg,
10 MHz: 89 deg, 11 MHz: 141.4 deg, 12 MHz: 163.0 deg,
13 MHz: 172.3 deg, 13.7 MHz: 183.82 deg.

Here is that list repeated in units of time, instead of degrees:

MHz ns delay
5.5 7.1
5.89 7.4
6 7.5
7 8.5
8 10.2
9 14.2
10 24.7
11 35.7
12 37.7
13 36.8
13.7 37.3

I would have to graph this on a log frequency plot to see the
frequency breakpoints, but I think this looks a lot like a short piece
of transmission line below about 6 MHz and like a resonator above
that. I expect the delay to start to fall at higher frequencies as
the turn-to-turn capacitance takes over.

What do you see?