Loading Coils; was : Vincent antenna
 

On Sat, 1 Dec 2007 21:47:47 -0500, "AI4QJ" wrote:


I dearly would like to see them sign on to the notion that a coil has
some inherent, fixed delay characteristic such as you describe (you
are describing that aren't you, now's the time to correct this mistake
of mine if I have made one).

In an inductor, current lags voltage. If you connect a resitor and a coil in
parallel and apply AC, EE101 tells you that, although the phase of the
voltage across them stays the same, the current is "delayed" by the phase
angle in the inductor when compared to current in the resistor. So, yes, in
this very fundamental sense there is a fixed delay. If this weren't so, I
assure you the world we live in just wouldn't be the same and there would be
no such thing as ham radio ;-))

Hi Dan,

I will then proceed to interpret this as to mean I made no mistake,
and a coil (not a coil and resistor, nor a coil and something else, I
did not ask about externalities) exhibits a fixed delay. Elaboration
is equally unnecessary. Correct me if you meant something else; but,
please and again, do not inject other issues into what I have written.
If you feel that you must, I have to say this is not what is being
discussed and that your concerns are not representative of the topic.
I have no interest in belaboring the obvious.

Do you, or can you (as has Cecil, and presumably Arthur) assign an
immutable angle (at one frequency) value that is inherent in Tom's or
Cecil's coil? I care little if it is correct, demonstrable, or can be
derived from any principles - simply can you offer a fixed
quantifiable? If you find this a strange request, then I would again
suggest you have missed the boat. This is not a flame, because it
sank a long time ago with all hands on board.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

On 1 Dec, 18:03, (Richard Harrison) wrote:
Art wrote:

"He was found to be insane and put in the tower."

Rudolph Hess was thought to be insane and put away for life after
piloting an aircraft to London. I had never heard that Hess was a
messenger from the German High Command. Considering the message, he
should have been respected.

Ambassador Joe Kennedy`s assessment wasn`t far off the mark. Without
massive foreign help, Hitler`s disregard of his general staff, and his
premature panic attack of the Soviet Union, when his forces were already
fully occupied, the Battle of Britain would have been lost by the
British.

From a vantage point afar from danger you under estimate the British.
You would have all surrender without a fight? Your admiration of the
german army in its quest to deny freedom to the masses is certainly
a shock to me. You have lost all respect by thumbing your nose
at those who gave of their lives for the cause of freedom while
others stood by aloof. Not once did I see a mustang in the air
as the luftwaffe excersed their might during those early years.
In fact, I did not see one plane from the army air force during
those years,only hurricains and spitfires. But I am glad the U.K.
was free and able to supply landing space when the enemy turned
its eyes away from our shores and thus dashed your hopes.
The enemy airforce by that time had become just a shadow of it's
former
self when the battle of Britain was decided leaving them nothing to
provide a blitzcreeg prior to any advance that had proved succesful
before. To cross the English channel in a time of war
has never been easy no matter which direction one is travelling,
history proves that.



The apes on Gibralter and the crows in the Tower of London
would have been of little help. Hitler`s forces had excellent training
and equipment. They were also accustomed to winning and quickly too.

Were you wearing a uniform supplied by Germany at that time?



Thankfully, Hitler made mistakes which doomed his enterprise.

Best regards, Richard Harrison, KB5WZI

Loading Coils; was : Vincent antenna
 

*Here is another way of looking at the coil current.*

Every wave must start with a wave front, some kind of initial small step
increase in the voltage and current.

This initial increase in voltage and current must enter the coil by
charging the space around the wire to some voltage, which requires
current to complete. This requires power and effectively 'charges' some
length of coil wire to some energy level, identical to charging a
capacitor. The initial wave front is moving, so we can think of the
capacitor (wire) behind the wave front as being charged and the
capacitor in front of the wave front as being uncharged.

As the wave front enters the coil, a small initial length of the coil
will be charged, with the stored energy located at a radial distance
from the wire. Within close radial distance of a coiled wire, we have
the adjacent coils and the wire on the other side of the coil. Both are
within the radial energy field expansion from the small initial length
of coil freshly charged by the initial wave.

The layers of coils can be considered as a series of capacitors, each
spaced at a distance equal to the coil turn spacing. The initial field
charges this series of capacitors at a velocity of field propagation.
The length of time required to charge the series of capacitors is the
time it takes for a wave traveling at the speed of light to travel the
length of the coil, not the wire length contained within the coil. This
explains the short time required for the initial pulse to be detectable
across the coil.

Obviously, this series of capacitors is shorted together by a path much
longer than the distance between coil windings. The wave front
continues down and around this longer path, taking a period of time
equal to time of travel of light traveling the length of the wire as if
it were stretched straight. Again obviously, while part of the energy
of the wave front has been stored in the capacitors of the adjacent
coils resulting in a wave front with diminished power, the reduction
would be a division between the series capacitors and the forward path
along the wire.

We must consider the magnetic field in this analysis. The initial step
voltage that is picked will determine the current which flows as a
result of the wire size and the surrounding materials, just as it does
for a transmission line. The initial step current will be steady (DC)
once the wave front has passed any point on the coil. The increasing
magnetic field in the axis of the coil is a result of the increasing
distance traveled by the wave front along the coiled wire, leaving a
steady state current and voltage (and unchanging magnetic and electrical
field) in place at points on the wire passed by the wave front.

The establishment of the steady magnetic field must be accompanied by a
changing magnetic field at the wave front. This magnetic field passes
the wire on the opposite side of the coil and induces a back voltage
before the initial wave front can follow the wire around the coil
circumference to reach the far side. As a result, the wave front
encounters a back voltage and current after the initial front has passed
a very short distance into the curved coil wire.

Please notice that the wave front described is equivalent to a square
wave on the forward face of the wave. A complete sine wave would be
made of successive rectangular waves, each of the appropriate length and
magnitude needed to compose a smooth sine wave as a final construction.

Assuming that the wave front will be traveling on a straight wire before
it enters the curved wires of the coil, the impedance of the wire will
change at the junction of straight and bent where the wire comes close
to the adjoining coil. This will cause a small reflection. There will
be a second reflection when the wave front encounters the reverse
voltage generated by the magnetic field that has crossed the coil, which
acts to cause a change in the impedance of the wire. Once traveling in
a relatively steady state along the curved portion of the coil wire, the
impedance would continue to change slowly as the wire winds between
environments from one coil end to the other. (Remember, the impedance
of the wire is the ratio of voltage to current detectable on the wire.)

Eventually the wave front will reach the far end of the coil where it
will encounter a new environment. A reflection will occur or not,
depending upon the end conditions. The amount of power stored in the
coil when the wave front reaches the coil end is the steady state
voltage X current X time. The time term is the time required for the
wave front to travel the length of wire in the coil.

73, Roger, W7WKB

Loading Coils; was : Vincent antenna
 

"AI4QJ" wrote in
:


"Owen Duffy" wrote in message
...
....
That didn't come out very clearly. As I understand it, Cecil argues
that there is substantial phase change in the forward and reflected
wave components when considering the helix as a transmission line.

I don't know if this is too simplistic but here goes:

The forward wave maintains it's phase as it encounters a new purely
resitive medium (like a straight copper wire or PCB trace). The
reflected wave that goes back into the helix transmission line refects
as a mirror image of the forward wave, just as light would reflect
from a partial mirror. This indeed would be a phase change relative to
the incident wave, approx. 90 degrees TIME or about 62.5 nsec at 4MHz
in the example under consideration. From here we can go on to discuss
the amplitude of the reflected wave and what it takes to cause
resonance and a 1:1 standing wave to appear. The standing wave will
not have a time phase shift so it cannot be used to measure delay, but
voltage and current will of course have a 90 degrees distance phase
shift across the transmission line.

I am open to correction on this.

The seems to me a bit confused, and I can't really understand it.

Looking at the coil Tom used:

If you use the inductance calculator at
http://hamwaves.com/antennas/inductance.html to determine Beta, you get
2.008 rad/m. The coil is .254m long, so that suggests a one-way phase
delay of 0.51 rad, or 29.2°. Some suggest that this coil will replace the
equivalent electrical length in a quarter wave monopole to shorten it
with inductive loading, and irrespective of the position of the loading
coil... which is not consistent with experience that a larger loading
coil is needed the further it is from the base.

One of the proponents posted on eham, the following solution to a loading
coil for 160m: "The VF of a 6" dia., 4 TPI coil on 160m would be about
0.02. Whatever number of degrees you want the coil to occupy, wind it
accordingly.", note the independence of coil size and location on the
monopole.

Owen

Loading Coils; was : Vincent antenna
 

"AI4QJ" wrote in
:

....
Owen,

What I did was use the basic impedance calculations:
....

You are performing lumped analysis where the current is uniform through
the coil, and there is no propagation delay.

The other solution that is being discussed is to treat the helix as a
transmission line with distributed R, L, G and C. That is what the
calculator that I gave the link to does. It implements the technique
described by the Corums and others, see the links.

The key thing is that the transmission line solution passes to lumped
elements when the coil length is sufficiently short, so they are not
inconsistent. It is questionable whether the transmission line solution
is worth the trouble for short coils.

Another practice by some is to assert that the helix substitutes
Beta*CoilLength radians of unloaded conductor... but I have not seen a
proof of why that can be done, nor does it seem sensible in the general
case.

Owen

Loading Coils; was : Vincent antenna
 

On Sat, 01 Dec 2007 20:28:27 -0800, Roger wrote:

*Here is another way of looking at the coil current.*

Every wave must start with a wave front

Hi Roger,

That, in a sense, sums up what Tom offers at his page (although I am
heavily editing you and outrageously paraphrasing him).

To go even further, and to the matter of measurement, especially in
the problematic use of leads that introduce error; there are TWO ways
for your "wave front" to arrive at the other end of the coil. One is
conduction, the other radiation. To this point in the discussion,
conduction has been the sole consideration (strange too, given the
hysterical outrage over treating the coil as a lumped load that so
often attends this topic).

Clearly radiation arrives by a more direct route, and given the
disproportionate size of the wavelength in comparison to the size of
the coil, the coil is for all intents and purposes transparent to the
propagation of the wave. This is not so for the helix of a TWT, nor
for the deliberate coil design of the helical antenna. However, at 80
meters, any point at the other end of a 10 inch coil is going to be
steamrollered into oblivion.

Tom's commentary hints at this, although the measurement provided is
lacking in detail to support this thesis.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

art wrote:
On 1 Dec, 12:44, Richard Clark wrote:
On Sat, 1 Dec 2007 11:56:55 -0800 (PST), art
wrote:

You pick a very poor place to talk about cowardice!
At that time Mr Kennedy Snr stated that islands of Britain
could not possibly stave off the armies that had overun Europe
Hi Arthur,

This week in class I learned from Ambassador Thomas Graham that
Hitler's second in command came to England and asked Neville
Chamberlain to reject Hitler's conditions for moving into
Czechoslovakia. He informed Chamberlain that the German High Command
was ready to topple Hitler if England showed strength.

We all know the rest of the story....

Yup. He was found to be insane and put in the Tower.
Germany did not want interference by Gt Britain.
In September 3rd 1939 Gt Britain was alone in
declaring war against Germanies gigantic armies.
That is what you have to do if you are the Worlds
policeman. Doing what is right regardless of the consequences
Pity the U.S. is unable to do the same.
Think how many countries the US government has
invaded since they took on the job and it looks
like there is more to come. Freedom fighters from
all over the World knew that there was a place to
go for the defence of freedom,and they came and
joined with us. Front and centre were the Polish
fighters with out which the British homeland
was in danger.The American ambassador fled to
home soil while the King and Queen stayed put.
It was a couple of years before the U.S. had
to join the fray and there was a Country still
there that they could join to carry on the fight.
It wasn't easy during those times but the British
held fast and resolute.
And nobody can take those proud times away that away.

Art Unwin KB9MZ....XG (uk)

Art,

You are a historical revisionist.

Dave K8MN

Loading Coils; was : Vincent antenna
 

On Dec 2, 12:19 am, "AI4QJ" wrote:
"AI4QJ" wrote in message

The location on the monopole may make a difference. Since a standing wave is
present, the location on the antenna will define the amount of current in
the coil. Mounting near the feedpoint is at a high current point and this
will increase ohmic losses. At approximately the center of the whip, the
current (and ohmic loss) will be minimal. However, more inductance will be
needed in the center location. thus more wire. More wire means more
resistance. In spite of that, many say that the most efficient location is
at near the center of the whip and intuitively I think this generally
correct as long as you use heavy wire.

It does make quite a difference. And this one one part that
bugs me about the taper/delay dilemma.
A coil loaded antenna actually needs more wire than the
comparison 1/4 wave monopole.
I used one of Reg's programs to churn some numbers up.
"Vertload"

The program is metric. I started with a 3m whip, and used a
..3 meter long loading coil, 100 mm diameter, which is close to
four inches. The antenna was tuned for 3.800 mhz, and used
2 ohms as the ground loss.
The coil came out to a 171 turns per meter, or a .17 dia/pitch
ratio.
This first example gave the total height of 3.3m tall overall,
and the coil was at .01m from the base, and the stinger
above the .3m long coil was 2.990m tall. I used 3m of
whip regardless of the coil height.
The base load version needed 51 turns of coil, which
was 16.31 m of wire plus the 3m of the whip. 19.31 m
of wire total. The efficiency was appx 14.49% vs the 1/4 wave.
Then I tried a center load.
To keep the same turn ratio, I had to use a longer coil.
..44m vs the .3m of the base load. Needed 75 turns,
with a coil wire length of 23.92m. 26.92m total wire with the
whip. The efficiency was 24.89 %.
Then I tried an appx 2/3 coil level with 2m base whip,
and 1m stinger. Again, to use the same coil stock,
you would have to lengthen the coil to .53m vs the .3m of
the base load. Would need 90 turns, with a wire length
of 28.69m. 31.69m total wire length with the whip.
The efficiency was 28.02 %.

You actually need more wire than the equal 1/4 wave whip.
Say a monopole at 3.8 mhz is 61.57 ft tall.
The appx 9.84 ft whip base loaded needs 63.35 ft of wire.
The center load needs 88.32 ft of wire.
The 2/3 load needs 103.97 ft of wire.
But it's the still most efficient of the three assuming
no overly high coil resistance.

To me, the coil current taper/delay, etc issue is basically
a non issue. It doesn't really matter to me one way or
the other as the design of the antennas will not change
a whit. Of course, it's nice to know exactly how it
happens, but it's not going to change the design
of the short verticals as far as coil placement, etc.
The optimum locations for those are already well
known, and will not be effected no matter how
thick the lather is whipped up on this NG.. :/
BTW, the optimum coil locations match the
"lumped" theory so close as to make me wonder
why anyone wastes so much energy worrying about
it.. But.. That's just me. I have many things to do and
worry about besides radios and antennas. So I choose
what I do worry about with some care. :)
This "problem" isn't one of them.. lol..
MK

Loading Coils; was : Vincent antenna
 

AI4QJ wrote:
In an inductor, current lags voltage. If you connect a resitor and a
coil in parallel and apply AC, EE101 tells you that, although the phase
of the voltage across them stays the same, the current is "delayed" by
the phase angle in the inductor when compared to current in the
resistor.

No, it isn't - the phase of the current around the circuit has to stay
the same. Think of the simplest possible circuit: an AC voltage source
(of zero internal impedance) with one terminal wired to R, lumped L in
series, and directly back to the other terminal of the AC source. If the
phase of the current were delayed through L as you suggest, there would
then be a difference in phase between the two terminals of the AC
source... which is obviously not true.

It's the magnitude and phase of the voltage that varies at different
points around the circuit; but the magnitude and phase of the current
has to remain the same all the way around the loop. In more formal
terms, Kirchhoff's current law applies all around the circuit; and it
most certainly applies between the two terminals of a lumped inductance.

If this weren't so, I assure you the world we live in just wouldn't be
the same

Well, you're certainly right about that :-)

What isn't sufficiently understood is that loading by pure lumped
inductance is responsible for almost all the properties of a
physically short loaded vertical. This is easy to see for base loading,
where lumped inductance at the feedpoint is simply compensating for the
capacitive reactance of the physically short whip.

The same remains true when the loading inductance is moved further up
the whip (progressively increasing the inductance, of course, in order
to maintain a zero reactance at the feedpoint). Loading by pure lumped
inductance explains all the well-known observations: the need for more
inductance if the coil is located further up the whip; the relatively
constant magnitude and phase of the current in the part of the whip
below the loading inductance; the large step increase in voltage across
the inductance itself; and the very rapid decrease in current in the
section above the loading inductance, tapering to zero current at the
top and accompanied by a very large electric field.

Note again: all the above is explained using the classic behaviour of
lumped inductance, with ZERO difference in current magnitude and phase
between its two terminals.

Now what changes when we replace a theoretical lumped inductance with a
physically realizable coil? The main difference is that the real-life
coil occupies a significant fraction of the total physical height of the
antenna. In addition to providing inductance, the coil is now behaving
to some extent like a helically-wound section of the complete antenna.
Now it is completely reasonable to expect some 'antenna-like' behaviour
from the coil: there will be some radiation from the coil itself,
accompanied by some decrease in current with distance along the coil. We
also expect some phase shift in current between its two ends.

This 'antenna-like' behaviour in a physically long loading coil is
completely reasonable and to be expected. However, it will be difficult
to explain in detail because the 'antenna-like' properties of the coil
will be strongly influenced by the other parts of the antenna. (This
also means that measurements made on a coil in isolation will have very
limited relevance to the behaviour of the coil as part of a complete
antenna.)

There may be several different valid explanations, each looking at the
problem from a different viewpoint - no problem about that, of course.
But there will also be several INvalid explanations... so how do we tell
the difference?

All the valid explanations will have at least one thing in common. They
will ALL be able to handle the boundary condition that, when the
physical size of the coil tends towards zero, every part of its
behaviour tends towards the classic behaviour of pure lumped inductance.
In particular for this part of the discussion, the phase shift in
current between its two terminals MUST tend to zero. Now that the
loading has become pure inductance, any valid explanation must still be
able to explain all the major features of the loaded whip, as identified
above.

In other words, any explanation MUST be able to handle that boundary
condition smoothly and effortlessly, without any need for a sudden
change in its own rules and assumptions. If it cannot do that, then
logic tells us that explanation cannot be correct. For example, if at
the boundary it is still demanding a phase shift in current between the
two terminals of a lumped inductance, that cannot be correct. If it
demands that lumped inductance behaves differently in antennas than it
does in any other circuit, then again it cannot be correct.

It's not me making these rules, by the way - just recognising that they
exist, and insisting that they apply.

Boundary conditions that join up with existing knowledge are a very
useful 'logical razor' to slice and dice ideas that fail to pass those
tests. In classical logic this method is called 'reductio ad absurdum',
but that's only the Latin for something that everybody knows:

"If it don't make sense, it kain't be right."

Unfortunately, some people seem to be immune to this, or want to
negotiate waivers for their own particular ideas. Progress comes from
recognising that there are no exceptions, and being prepared to let go
of cherished ideas if it is shown that they don't work.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Loading Coils; was : Vincent antenna
 

On Dec 2, 2:46 am, wrote:
On Dec 2, 12:19 am, "AI4QJ" wrote:

"AI4QJ" wrote in message
The location on the monopole may make a difference. Since a standing wave is
present, the location on the antenna will define the amount of current in
the coil. Mounting near the feedpoint is at a high current point and this
will increase ohmic losses. At approximately the center of the whip, the
current (and ohmic loss) will be minimal. However, more inductance will be
needed in the center location. thus more wire. More wire means more
resistance. In spite of that, many say that the most efficient location is
at near the center of the whip and intuitively I think this generally
correct as long as you use heavy wire.

BTW, if you raise the coil, you generally will see maximum current
at the coil, not at the base.
This is another thing that bothers me about the taper/delay theory..
Myself, I think the usual "short" loading coil acts pretty much as
in lumped theory. To me, it acts more as a single unit, rather than
the many feet of wire acting as a mere extension to the whip.
These two things kind of blow the "90 degrees of wire theory"
in my mind at least..
If that were the case, you would think the amount of wire, coil turns
should stay the same no matter the location. But also, even with the
physical length of wire being coiled up, I would also still expect to
see maximum current at the base of the whip, same as a 1/4
monopole.
But this is not the case. Seems to me it's been shown many times
that if you elevate the coil, the current distribution is fairly
linear
up the lower whip, and you will see a slight current maximum at the
coil, not at the base.
I don't think you would see that current max at the coil if it were
not acting pretty much as a lumped inductor.
But thats just my take part 2..
MK