OK, I have been accused of being wrong, claiming that current across the
antenna loading coil is or can be different at its ends.
I and "my camp" say that we are seeing somewhere 40 to 60 % less current at
the top of the coil, than at the bottom, in other words, significant or
noticeable drop.
W8JI and "his camp" are claiming it can't be so, current through the coil
has to be the same or almost the same, with no significant drop across the
loading coil.

Let's start the fresh thread and trace step by step where I went wrong.

Just reminder that we are talking typical situations, as for example real 40
m (or 80 m) mobile whip with loading coil about 2/3 up the radiator. We are
talking about resonant electrical quarter wave monopole. We are talking
about standing wave RF current that can be measured with RF ammeter and is
shown and plotted in modeling programs like EZNEC.

Here we go:

wrote in message
Let's focus on one thing at a time.

You claim a bug cather coil has "an electrical length at 4MHz of ~60
degrees". That concept is easily proven false, just like the claim a
short loaded antenna is "90-degree resonant". Both can be shown to be
nonsense pictures of what is happening.

Assume I have a 30 degree long antenna. If the loading inductor is 60
electrical degrees long, I could move it anyplace in that antenna and
have a 90 degree long antenna.

We all know that won't happen, so what is it you are really trying to
say?

73 Tom


OK lets get me some educating here.
I understand that, say quarter wave resonant vertical (say 33 ft at 40m) has
90 electrical degrees.
Is that right or wrong?

The current distrubution on said (full size) vertical is one quarter of the
wave of 360 deg. which would make it 90 degrees. Max current is at the base
and then diminishes towards the tip in the cosine function down to zero.
Voltage distribution is just opposite, min at the base, feed point and max
at the tip. EZNEC modeling shows that to be the case too.
Is that right or wrong?

If we stick them end to end and turn horizontal, we get dipole, which then
would be 180 deg. "long" or "180 degrees resonant".
If not, what is the right way?

If I insert the coil, say about 2/3 up (at 5 ft. from the bottom) the
shortened vertical, I make the coil size, (inductance, phys. dimensions)
such that my vertical will shrink in size to 8 ft tall and will resonate at
7.87 MHz.
I learned from the good antenna books that this is still 90 electrical
"resonant" degrees.
Maximum of current is at the feed point, minimum or zero at the tip.

If you stick those verticals (resonant) end to end and horizontal, you get
shortened dipole, with current distribution equal to 180 degrees or half
wave. Max current at the feed point, minima or zero at the tips. (RESONANT
radiator)

How many electrical degrees would that make? How do you arrive at that?
Why is this a nonsense?

Can we describe "pieces" or segments of the radiator as having proportional
amount of degrees corresponding to their physical length, when excited with
particular frequency?

If I can be enlightened about this, we can go then to the next step.

Answers, corrections please.

Yuri, K3BU

On Thu, 23 Mar 2006 12:50:32 -0500, "Yuri Blanarovich"
wrote:

Let's start the fresh thread and trace step by step where I went wrong.

Hi Yuri,

Are you then abandoning your web page?

You know, it would seem to be better effort to stick with the
demonstrables there and to make sense of them, than to wander the
intellectual landscape of "theory."

OK lets get me some educating here.
I understand that, say quarter wave resonant vertical (say 33 ft at 40m) has
90 electrical degrees.
Is that right or wrong?

If you cannot define your limits of error, then Cecil is bound to do
it for you and plug in +/- 50% to make any assertion laughable, such
as:

Can we describe "pieces" or segments of the radiator as having proportional
amount of degrees corresponding to their physical length, when excited with
particular frequency?

You've left too many things out to agree to more than a rather
insubstantial maybe. If that's sufficient, then there's really no
need to go any further, is there?

73's
Richard Clark, KB7QHC

Yuri wrote,

" I and "my camp" say that we are seeing somewhere 40 to 60 % less
current at
the top of the coil, than at the bottom, in other words, significant or
noticeable drop.
W8JI and "his camp" are claiming it can't be so, current through the
coil
has to be the same or almost the same, with no significant drop across
the
loading coil. "

I'm not sure who all you put in W8JI's "camp," but I'm absolutely sure
that I've read recent postings by W8JI himself that affirm that there
can be significant difference in current between the ends of the
loading coil. What I DO see him posting is that if the difference is
large, the antenna design is almost certainly suboptimal.

If you want to understand how a loading coil with zero capacitance to
the outside world can actually work, I suggest you read the Joseph
Boyer article from "Ham Radio" magazine some 28 years ago. Ian White
gave a more complete reference to that article in one of his postings
in the interminable thread. I'm always happy to ship out a copy of
that article for the cost of postage.

Cheers,
Tom

Yuri, you have neglected at least one important unit of measu namely,
the action integral of the 'active antenna' times the current
[ampere*degrees].

For simplicity, assume a constant one ampere is flowing in a physical 15
degree antenna. The answer is 15 ampere*degrees. In a true 1/4
wavelength antenna the answer is 90 ampere*degrees. The shortened
antenna is [=] a tuned 15 degree antenna NOT a 90 degree antenna!!

In a real shortened antenna, the base current may be assumed, to a first
approximation, as constant from the base to the loading coil. If that
portion of the antenna is 10 degrees, then 10 ampere*degrees is the
action integral.

The current in the top section can be assumed linear from the value at
the top of the coil to the tip where I=0. This is a triangle [or a sin
function that is close to linear] that can solve to two possible values.
The first is based on one ampere exiting the top of the coil and the
solution is 1/2*1 ampere*5 degrees = 2.5 ampere degrees. The second is
based on a sinusoidal distribution from the tip to the 5 degree point at
the top of the coil where the current is 0.087 ampere. [The sin of 5
degrees is 0.087.] So, the action integral is 1/2*0.087 amperes*5
degrees = 0.218 ampere*degrees.

The practical application deals with the efficiency of the antenna. Is
that tuned 15 degree long antenna a 12.5 ampere degree antenna; or, is
it a 10.218 ampere degree antenna? [That's approximately a difference of
1 dB in antenna performance.]

The discussion here for the past three infinities is: What is happening
inside the tuning coil? Is there a change in current amplitude? If so,
please explain the physics. Is there no change in current amplitude? If
so, please explain the physics.

The coil is physically less than one degree in length, but contains
enough wire to be a significant portion of a wavelength. Interwinding
capacitance and distributed inductance can make the coil look like a
transmission line.

The flux density from each turn in an air core coil construction
diverges as one progresses along the coil [the flux density at turn #2
is higher than at turn #60 for example]. Restated, there is a leakage
inductance along the coil. The flux density has a propagation time in
free space of approximately 0.5E-9 seconds. Is this significant? [I
don't think so]

In the tuning coil there exists an interwinding capacitance and a
capacitance to "structure" [whatever that is].

In 1958, my college days, we were instructed to ignore the coil and
solve the antenna as two separate sections with an infinitesimal gap at
the junction. I never liked that model then and I don't like it today!
[It still allows two solutions][We were instructed that the current is
constant].

So, we have two well entrenched positions: the current does not change
in the coil, and, the current changes in the coil. Like World War I, it
is trench warfare with much bloodshed [reputation] on both sides.

Due to leakage inductance, I suspect that the current does change within
the air core coil but the change is much less than that implied by the
simple sin wave distribution [sin 5 degrees] used above.

Below the coil the H field dominates. Above the coil the E field
dominates. The transition from E to H occurs across [within] the coil.
That leads me to conclude that there is a change of current within the
coil.

In any event, the 15 degree antenna is still a 15 degree antenna! The
question is: what about that 1 dB difference in the modeling analysis?

This simple engineer is still unconcerned about one dB difference and
it's impact on antenna gain. If the science side of this discussion
can't agree, then I'll simply continue to operate mobile and not worry
if my signal is one dB stronger or weaker at the receiving end of the
path!! It is what it is!!

# # #

Yuri Blanarovich wrote:

OK, I have been accused of being wrong, claiming that current across the
antenna loading coil is or can be different at its ends.
I and "my camp" say that we are seeing somewhere 40 to 60 % less current at
the top of the coil, than at the bottom, in other words, significant or
noticeable drop.
W8JI and "his camp" are claiming it can't be so, current through the coil
has to be the same or almost the same, with no significant drop across the
loading coil.

Let's start the fresh thread and trace step by step where I went wrong.

Just reminder that we are talking typical situations, as for example real 40
m (or 80 m) mobile whip with loading coil about 2/3 up the radiator. We are
talking about resonant electrical quarter wave monopole. We are talking
about standing wave RF current that can be measured with RF ammeter and is
shown and plotted in modeling programs like EZNEC.

Here we go:

wrote in message

Let's focus on one thing at a time.

You claim a bug cather coil has "an electrical length at 4MHz of ~60
degrees". That concept is easily proven false, just like the claim a
short loaded antenna is "90-degree resonant". Both can be shown to be
nonsense pictures of what is happening.

Assume I have a 30 degree long antenna. If the loading inductor is 60
electrical degrees long, I could move it anyplace in that antenna and
have a 90 degree long antenna.

We all know that won't happen, so what is it you are really trying to
say?

73 Tom



OK lets get me some educating here.
I understand that, say quarter wave resonant vertical (say 33 ft at 40m) has
90 electrical degrees.
Is that right or wrong?

The current distrubution on said (full size) vertical is one quarter of the
wave of 360 deg. which would make it 90 degrees. Max current is at the base
and then diminishes towards the tip in the cosine function down to zero.
Voltage distribution is just opposite, min at the base, feed point and max
at the tip. EZNEC modeling shows that to be the case too.
Is that right or wrong?

If we stick them end to end and turn horizontal, we get dipole, which then
would be 180 deg. "long" or "180 degrees resonant".
If not, what is the right way?

If I insert the coil, say about 2/3 up (at 5 ft. from the bottom) the
shortened vertical, I make the coil size, (inductance, phys. dimensions)
such that my vertical will shrink in size to 8 ft tall and will resonate at
7.87 MHz.
I learned from the good antenna books that this is still 90 electrical
"resonant" degrees.
Maximum of current is at the feed point, minimum or zero at the tip.

If you stick those verticals (resonant) end to end and horizontal, you get
shortened dipole, with current distribution equal to 180 degrees or half
wave. Max current at the feed point, minima or zero at the tips. (RESONANT
radiator)

How many electrical degrees would that make? How do you arrive at that?
Why is this a nonsense?

Can we describe "pieces" or segments of the radiator as having proportional
amount of degrees corresponding to their physical length, when excited with
particular frequency?

If I can be enlightened about this, we can go then to the next step.

Answers, corrections please.

Yuri, K3BU

Dave wrote:
. . .
The practical application deals with the efficiency of the antenna. Is
that tuned 15 degree long antenna a 12.5 ampere degree antenna; or, is
it a 10.218 ampere degree antenna? [That's approximately a difference of
1 dB in antenna performance.]
. . .

I believe you're comparing the field strengths from two antennas both
driven by the same current. If you drive them with the same power, a
more fair comparison, you'll find a negligible difference in field
strength. Efficiency is another issue, solely related to losses in the
antennas. Without knowing what those losses might be, we can't say
anything about the relative efficiency. In practice it'll probably be
extremely closely the same also.

Roy Lewallen, W7EL