A little more on missing degrees
 

In item 2 you make an unsupported statement: "Give that the coil is 90
degrees at the self-resonant frequency,..."

Self resonance only means that the capacitive and inductive reactances,
both distributed, are equal. That does not validate a 90 degree
assumption. Without that validation, IMO, the subsequent discussion is
questionable.



Cecil Moore wrote:

Dave wrote:

I gave up on the 'missing degrees' and all variations topic about 1
month ago. Hit the KILL Button and read on!


For those who didn't give up, here is a summary of what I
was able to do with EZNEC. This exercise should be able
to be repeated in the real world.

1. Using the helix feature of EZNEC, I created a 100 turn
octagonal coil, 6 inches in diameter, 4 turns per inch.

2. I installed it as a base loading coil over a mininec
ground plane and removed turns until it was self-resonant
on 4 MHz. That left a total of 69 turns on a 1.435 foot
long coil. Give that the coil is 90 degrees at the self-
resonant frequency, I calculated a velocity factor of
0.023 for the coil.

3. The coil was then trimmed to half size, i.e. 34.5 turns.
Assuming it was then 45 degrees long, the Z0 was determined
to be approximately 2200 ohms by looking at the feedpoint
impedance reported by EZNEC. 45 degrees from 0-j0 on the
Smith Chart is at -j1.0.

4. A stinger was added to the above 45 degrees of coil to
bring the antenna back to resonance on 4 MHz. It took 7 ft.
of stinger, or 10.2 degrees. 10.2 degrees from 0-j*infinity
on the Smith Chart is at -j4.8.

5. The ratio of -j4.8/-j1.0 is the ratio of the Z0 of the
coil to the Z0 of the stinger. If the Z0 of the coil is
indeed 2200 ohms, the Z0 of the stinger is 458 ohms, just
about where it should be. The impedance discontinuity
provides the "missing" ~35 degrees of the antenna.

6. Using Dr. Corum's equation for velocity factor yields
0.02 for that coil, a value 13% lower than the one
predicted by EZNEC, well within the ballpark for
expectations.

My conclusions: The delay through a loading coil is in
the tens of degrees. The delay through the elements of
the antenna do not add up to 90 degrees. In the above
EZNEC example, the delay from feedpoint to the tip of
the antenna is only 55 degrees. The "missing"
degrees are provided by the impedance discontinuity
between the coil and the stinger. There is no real-
time delay associated with those "missing" degrees.

A little more on missing degrees
 

On Mon, 1 May 2006 22:59:20 -0500, (Richard
Harrison) wrote:

Richard Fry wrote:
"Such networks don`t add or subtract electrical degrees, however. They
only reduce/cancel the natural reactance of the physical radiator in
use."

True if the only mismatch is reactance. A too-long antenna can be
electrically shortened for matching purposes by tuning it to resonance
with the proper series capacitance. A too-short antenna can be
electrically lengthened for matching purposes by tuning it to resonance
with the proper series inductance.

Reactance varies quickly near the resonant length. Radiation resistance
varies more slowly tending to increase at a steady rate as the antenna
is lengthened.

What radiates is current in a length of antenna. What gets current into
an antenna is a conjugate match. Reactance is zeroed out, and source and
load resistances are matched. That`s what`s needed for maximum power
transfer between generator and antenna.

Analysis may have been more abundant than needed for practical purposes.

The velocity of current through a coil has been disputed. Some said it
was almost instantaneous. That was new to me. The nature of inductance
is to produce counter emf which by Lenz`s law opposes current into an
inductance and temporarily delays current changes in an inductance. Only
in a pure resistance is there instantaneous correlation between voltage
and current.

Constraining the discussion to lumped circuit theory, the delay that
you speak of would seem to be relevant if one is measuring transient
response. However, for a steady-state a.c. current, is it not more
appropriate to describe the relationship as a phase lag between the
current through and the voltage across the inductor? Further, is it
not the case that such phase difference is nominally fixed at near 90
degrees (for a high Q inductor), and is it not true that the velocity
is nonetheless at the speed of light?


It is believed that the speed of light "c" is a speed limit on
electromagnetic waves. An action in one place must have a delayed
response elsewhere depending on distance.

I can imagine a wave launched at one of an inductor sweeping across its
length and ignoring the round and round path of the wire, but I don`t
know of any of the old authors in my collection who say that such a
short-cut happens. Conductors are the source of free electrons which
permit current flow and my experience is that electricity goes where it
is wired.

Best regards, Richard Harrison, KB5WZI

A little more on missing degrees
 

Dave wrote:
In item 2 you make an unsupported statement: "Give that the coil is 90
degrees at the self-resonant frequency,..."

Self resonance only means that the capacitive and inductive reactances,
both distributed, are equal. That does not validate a 90 degree
assumption. Without that validation, IMO, the subsequent discussion is
questionable.

Quoting from the Corum paper concerning self resonance
of a coil:

"The forward and backward traveling waves have superposed
to give this voltage standing wave distribution along the
resonator. There is a voltage null at the base, a voltage
maximum at the top, and a sine wave envelope along the
structure." That defines 90 degrees of coil.

For the standing wave, there are 90 degrees between a voltage
null and a voltage maximum. The voltage maximum at the top
of the coil corresponds to the current null existing there
because the current has no place to go. The voltage null at
the base corresponds to the current maximum there which is
a necessary condition for self resonance. There's 90 degrees
between a voltage null and a voltage maximum. There's 90
degrees between a current null and a current maximum.
--
73, Cecil http://www.qsl.net/w5dxp

A little more on missing degrees
 

Cecil Moore wrote:

SNIPPED

Quoting from the Corum paper concerning self resonance
of a coil:

"The forward and backward traveling waves have superposed
to give this voltage standing wave distribution along the
resonator. There is a voltage null at the base, a voltage
maximum at the top, and a sine wave envelope along the
structure." That defines 90 degrees of coil.

For the standing wave, there are 90 degrees between a voltage
null and a voltage maximum. The voltage maximum at the top
of the coil corresponds to the current null existing there
because the current has no place to go. The voltage null at
the base corresponds to the current maximum there which is
a necessary condition for self resonance. There's 90 degrees
between a voltage null and a voltage maximum. There's 90
degrees between a current null and a current maximum.

Under that definition my 8 foot high mobile antenna has a voltage
maximum at the top and a current maximum at the base and must,
therefore, be 90 degrees long. But, it is physically only 16 degrees
long [8/43.5 @ 5.37 MHz]. Now it is 5 degrees long above the top of the
coil and 10 degrees long below the coil ... ad nauseum [ for another 2
months ] ...

Where is the other 74 degrees?? This is the question that started this
2 month discussion.

Is there a fallacy in Corum's paper?

Does Corum's paper apply to a combination of a loading coil and
radiating elements?

My reasoning is as follows: if I draw a phasor diagram, I have +10
degrees phase shift from the feed point to the base of the coil. I can
then assume a +90 degree phase shift in the coil, classical inductive
response; then, the 'stinger', from the top of the coil to the tip of
the antenna produces a net -10 degree phase shift from both inductive[+]
and capacitive[-] effects resulting in a net 90 degree phase shift for
the full eight foot antenna.

Am I being too simplistic?

I conclude that I have a 16 degree long antenna with a feedpoint
resistance of ~13 ohms [ Rr = ~1.0 ohm and Rloss = ~12 ohms] with zero
ohms reactance [resonant]. [And that the phase shifts stated above are
fundamentally correct.]

A little more on missing degrees
 

Dave wrote:
Where is the other 74 degrees??

Please reference my other postings. It is all explained
there.

1. There are tens of degrees in the coil. That phase shift
is not instantaneous and obeys the VF of the coil.

2. There are tens of degrees in the impedance discontinuity
between the coil and stinger. That phase shift is instantaneous
and requires no delay.

3. There are tens of degrees in the stinger. That phase shift
is not instantaneous and obeys the VF of the stinger.

4. They all add up to 90 degrees.
--
73, Cecil http://www.qsl.net/w5dxp

A little more on missing degrees
 

Dave wrote:

Where is the other 74 degrees?? This is the question that started this
2 month discussion.

Is there a fallacy in Corum's paper?

Does Corum's paper apply to a combination of a loading coil and
radiating elements?

My reasoning is as follows: if I draw a phasor diagram, I have +10
degrees phase shift from the feed point to the base of the coil. I can
then assume a +90 degree phase shift in the coil, classical inductive
response; then, the 'stinger', from the top of the coil to the tip of
the antenna produces a net -10 degree phase shift from both inductive[+]
and capacitive[-] effects resulting in a net 90 degree phase shift for
the full eight foot antenna.

Am I being too simplistic?

I conclude that I have a 16 degree long antenna with a feedpoint
resistance of ~13 ohms [ Rr = ~1.0 ohm and Rloss = ~12 ohms] with zero
ohms reactance [resonant]. [And that the phase shifts stated above are
fundamentally correct.]

You don't need to go to anywhere near that much trouble. If you replace
the stinger with a lumped series RC to ground with the same impedance as
the stinger, you'll get nearly the same currents, both magnitude and
phase, at the top and bottom of the coil as you did with the stinger. No
"missing degrees" -- no "degrees" at all, in fact. No forward and
reverse traveling waves, no standing waves. No smoke and mirrors, no
bafflegab. Just plain old circuit analysis.

Roy Lewallen, W7EL

A little more on missing degrees
 

Roy Lewallen wrote:
You don't need to go to anywhere near that much trouble. If you replace
the stinger with a lumped series RC to ground with the same impedance as
the stinger, you'll get nearly the same currents, both magnitude and
phase, at the top and bottom of the coil as you did with the stinger. No
"missing degrees" -- no "degrees" at all, in fact. No forward and
reverse traveling waves, no standing waves.

No understanding of the laws of physics -
just 1001 shortcuts and rules of thumb -
consistent with the dumbing down of the
US educational system and amateur radio.
--
73, Cecil http://www.qsl.net/w5dxp

A little more on missing degrees
 

"Dave" wrote in message
. ..

Under that definition my 8 foot high mobile antenna has a voltage maximum
at the top and a current maximum at the base and must, therefore, be 90
degrees long. But, it is physically only 16 degrees long [8/43.5 @ 5.37
MHz]. Now it is 5 degrees long above the top of the coil and 10 degrees
long below the coil ... ad nauseum [ for another 2 months ] ...

Where is the other 74 degrees?? This is the question that started this 2
month discussion.


Dave,
your 8 ft mobile antenna is not 90 degrees long, you don't have zero
reactance at the feedpoint. You will have to insert the loading coil or
matching network to do that and that adds the missing degrees. (You might
have maximum current as far as the whip is concerned, but not maximum
current corresponding to the base of resonated whip, just fraction
corresponding what standing wave would supply for that tip o'antenna.)
Then you have drop of current along the coil, (missing degrees) and rest in
the stinger at corresponding degreed to the straight radiator. (Worst
efficiency of that length of antenna.).
As you start moving the loading coil up the antenna, you start increasing
the high current in bottom part of antenna, then drop along the coil, then
rest of the drop towards the stinger, down to zero. As you move coil higher,
you will have to add the turns in order to maintain resonance (90 degrees
overall, zero reactance at the feedpoint).
Looks like my idea about the role of impedance has some merit, Cecil is
hitting it with idea of "losing" some degrees at the impedance "bumps"
completing the picture of them mysteriously missing degrees, to dismay of
same current believers. So looks like degrees of mast, plus degrees of
impedance bump between the mast and coil, plus degrees of coil, plus degrees
of impedance bump between the coil and stinger, plus degrees of stinger
should add up to 90 degrees in resonant monopole or resonator, as some
antenna pioneers called it. Do we get it now more precisely? Or there are
still some "missing" degrees floating around?

73 Yuri, K3BU/m

A little more on missing degrees
 

We haven't been missing any degrees around here.
We hit the low 90's , while even still in late April.
It's May now, and still no obvious loss of degrees.
Feels like summer, the grass is green, and I feel
quite warm most every day. It's those people up
far north that miss degrees. :)
MK