Dish reflector
 

On Apr 22, 9:59*pm, Tom Ring wrote:
Tom Ring wrote:snip
Tom
*What you say it should be is guided by conventional teachings and my
designs are not conventional. Per conventional teachings it would be
snip
Art

Ok. *So what have you changed from a standard helical design that makes
it "not conventional" ?

Your original description sounded pretty much like a stock 1m band
helical, so if you've done something to pull it down 160:1 in frequency,
I'd love to hear what it is. *It must be simple and obvious, because you
didn't mention it in your post.

tom
K0TAR

Oh, I forgot.

Art, you need to google for "axial mode".

tom
K0TAR

Tom
I tried to share and I started with Gauss's law of statics. I never
really got into it hard because of the reaction to the first step.
Without an understanding of that first step it becomes impossible to
move further. Yes, I have made comments beyond that point but I also
left out certain factors because my work is not complete. The bottom
line is that the new antennas have been made and meet my expectations
up to this point but I have more to do. This group is not for antenna
debate it is for gottchas
by those who perceive themselves as experts and beyond the point of
debate.
Now I accept the group for what they are while enjoying my
achievements on the side.
As for you telling me what I need to do with respect to axial mode, I
know my own needs better than you.I think you will be better off
listening instead of posting starting with what Cecil has to say and
the difficulties that you are having in digesting.
Regards
Art

Dish reflector
 

Art Unwin wrote:
On Apr 22, 8:46Â*pm, Tom Ring wrote:
Art Unwin wrote:

The helix is four foot long and a foot diameter. The base Â*of the
reflector is 1.5 feet
snip
Art

A 1 foot diameter helix would be a design for the 1 meter band, not 160.
Â* You need to scale it up just a bit.

The diameter should be about 50 meters. Â*The reflector should be maybe
150 meters in diameter. Â*This is not going to fit in your back yard.

tom
K0TAR

Tom
What you say it should be is guided by conventional teachings and my
designs are not conventional.

To say the least...


--
Jim Pennino

Remove .spam.sux to reply.

Loading coils: was Dish reflector
 

Roy Lewallen wrote:
If you look at the transmission line
properties of a vertical, you see that the two conductors (the antenna
and ground plane) get farther and farther apart as the distance from the
feedpoint increases. This behaves like a transmission line whose
impedance increases with distance from the feedpoint and, in fact, a TDR
response shows just this characteristic. It's open circuited at the end,
so it behaves pretty much like an open circuited transmission line,
resulting in the same reflections and resulting standing waves you see
on a real antenna.

The Z0 characteristic impedance that matters is the
one that exists at the coil-stinger junction which
can be estimated from the single-wire transmission
line Z0 equation. It's usually in the neighborhood
of a few hundred ohms. For instance, a #14 horizontal
wire at 30 feet has a Z0 very close to 600 ohms
according to the formula.

One difficulty is accounting for the radiation, which
adds resistance to the feedpoint. I've never seen an attempt at
simulating it with distributed resistance, which I don't think would
work except over a narrow frequency range.

I have simulated such using EZNEC's wire resistivity
option. The resistance wire simulates the radiation
"loss" from the antenna. But for a standing wave
antenna, the "loss" to radiation is only about 20%
of the total energy stored on the standing wave
antenna. Therefore, a qualitative conceptual analysis
can be done assuming lossless conditions just as it
can be done with transmission lines.

But one
shortcoming of many antenna transmission line analogies is the attempt
to assign a single "average" or "effective" characteristic impedance to
the antenna, rather than the actual varying value. This is where a lot
of care has to be taken to assure that the model is valid in the regime
where it's being used.

Seems EZNEC automatically compensates for the varying Z0
so all we need to estimate is the single effective Z0 at
the coil to stinger impedance discontinuity.

There's no reason you can't also include a loading coil in the
transmission line model, and Boyer devotes much of the second part of
his article to doing just that. A solenoidal coil raises the
characteristic impedance of the length of "line" it occupies, because of
the increase in L/C ratio in that section. The traveling wave delay in
that section of the transmission line also increases due to the
increased LC product.

Are you saying the physics of the delay through a loading
coil changes between a traveling wave and a standing wave???
The standing wave is composed of a forward traveling wave
and a reflected traveling wave. They would experience the
same delay that you are talking about above.

So why didn't you use a traveling wave to measure the delay
through a loading coil??? Exactly how can the following
antenna current (from EZNEC) be used to calculate delay? The
current changes phase by 2.71 degrees in 90 degrees of
antenna. If the antenna was lossless, i.e. no radiation,
that current would not change phase at all.

EZNEC+ ver. 4.0
thin-wire 1/4WL vertical 4/23/2009 6:52:13 AM
--------------- CURRENT DATA ---------------
Frequency = 7.29 MHz
Wire No. 1:
Segment Conn Magnitude (A.) Phase (Deg.)
1 Ground 1 0.00
2 .97651 -0.42
3 .93005 -0.83
4 .86159 -1.19
5 .77258 -1.50
6 .66485 -1.78
7 .54059 -2.04
8 .40213 -2.28
9 .25161 -2.50
10 Open .08883 -2.71

--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Loading coils: was Dish reflector
 

On Apr 23, 7:06*am, Cecil Moore wrote:
Roy Lewallen wrote:
If you look at the transmission line
properties of a vertical, you see that the two conductors (the antenna
and ground plane) get farther and farther apart as the distance from the
feedpoint increases. This behaves like a transmission line whose
impedance increases with distance from the feedpoint and, in fact, a TDR
response shows just this characteristic. It's open circuited at the end,
so it behaves pretty much like an open circuited transmission line,
resulting in the same reflections and resulting standing waves you see
on a real antenna.

The Z0 characteristic impedance that matters is the
one that exists at the coil-stinger junction which
can be estimated from the single-wire transmission
line Z0 equation. It's usually in the neighborhood
of a few hundred ohms. For instance, a #14 horizontal
wire at 30 feet has a Z0 very close to 600 ohms
according to the formula.

One difficulty is accounting for the radiation, which
adds resistance to the feedpoint. I've never seen an attempt at
simulating it with distributed resistance, which I don't think would
work except over a narrow frequency range.

I have simulated such using EZNEC's wire resistivity
option. The resistance wire simulates the radiation
"loss" from the antenna. But for a standing wave
antenna, the "loss" to radiation is only about 20%
of the total energy stored on the standing wave
antenna. Therefore, a qualitative conceptual analysis
can be done assuming lossless conditions just as it
can be done with transmission lines.

But one
shortcoming of many antenna transmission line analogies is the attempt
to assign a single "average" or "effective" characteristic impedance to
the antenna, rather than the actual varying value. This is where a lot
of care has to be taken to assure that the model is valid in the regime
where it's being used.

Seems EZNEC automatically compensates for the varying Z0
so all we need to estimate is the single effective Z0 at
the coil to stinger impedance discontinuity.

There's no reason you can't also include a loading coil in the
transmission line model, and Boyer devotes much of the second part of
his article to doing just that. A solenoidal coil raises the
characteristic impedance of the length of "line" it occupies, because of
the increase in L/C ratio in that section. The traveling wave delay in
that section of the transmission line also increases due to the
increased LC product.

Are you saying the physics of the delay through a loading
coil changes between a traveling wave and a standing wave???
The standing wave is composed of a forward traveling wave
and a reflected traveling wave. They would experience the
same delay that you are talking about above.

So why didn't you use a traveling wave to measure the delay
through a loading coil??? Exactly how can the following
antenna current (from EZNEC) be used to calculate delay? The
current changes phase by 2.71 degrees in 90 degrees of
antenna. If the antenna was lossless, i.e. no radiation,
that current would not change phase at all.

* * * * * * * * * * * *EZNEC+ ver. 4.0
thin-wire 1/4WL vertical * * 4/23/2009 * * 6:52:13 AM
* * * * * --------------- CURRENT DATA ---------------
Frequency = 7.29 MHz
Wire No. 1:
Segment *Conn * * *Magnitude (A.) *Phase (Deg.)
1 * * * *Ground * * 1 * * * * * * * *0.00
2 * * * * * * * * * .97651 * * * * *-0.42
3 * * * * * * * * * .93005 * * * * *-0.83
4 * * * * * * * * * .86159 * * * * *-1.19
5 * * * * * * * * * .77258 * * * * *-1.50
6 * * * * * * * * * .66485 * * * * *-1.78
7 * * * * * * * * * .54059 * * * * *-2.04
8 * * * * * * * * * .40213 * * * * *-2.28
9 * * * * * * * * * .25161 * * * * *-2.50
10 * * * Open * * * .08883 * * * * *-2.71

--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Cecil
The problem in this debate is that others are concentrating on
resonance
where as you are thinking in terms of anti resonance which portends to
a higher impedance and also the condition of equilibrium. When
considering the boundary law
one must recognise that momentum increases and decreases twice per
period. Thus when considering the boundary laws the negative area of
the sine wave must be placed underneath the positive area such that
momentum is taken account of.
When the diagram provided by Best on this thread was shown what it
described was the period was extended by the containment within the
boundary and where that containment extended the period which is now
longer than the period of non containment.In one case you have
accelleration and deaccelleration which is depicted
as the emmission of energy or flux. Consevation of energy laws demands
that for balance we must take into account the energy or flux that
enters the boundary to maintain equilibrium which is depicted by the
negative area of the sine wave period
such that this area is placed directly under the positive area while
still remaining within the arbritrary boundary. Thus we have
effectively changed the period when looking at a coil where the slow
wave is now half of the original wave as is theresonant point is half
of the anti resonant point which in terms of Newton and Maxwell
represents the point of equilibrium. When using the resonant point in
terms of relativity ie Maxwell you are seeing movement of a charge
from "a" to "b" which when repeated is repetitive movement in a single
direction. When using the anti resonant point the charge returns to
the starting point and if time is regarded as /dt
then the charge only moves in the vertical direction. Thus in terms of
Earth mass consists of energy movement in the ":z" plan and with
respect to the Universe the energy movement is solely in the "x" or
"y": direction until this action is equated with an action from the
opposite direction as per the law of Newton. Thus like Einstein
viewing the same action of Newton this thread is viewing the same
problem where one is static and one is relative but never the less the
same problem but relatively different. Pure physics my dear Watson
viewed fron different vantage points., one takes equilibrium into
account where as the other doesn't.
Not "babble"' David just an explanation per classical physics which is
the sole and only root of both mechanical and electrical engineering
Best regards
Art Unwin KB9MZ xg(uk)

Loading coils: was Dish reflector
 

Art Unwin wrote:
The problem in this debate is that others are concentrating on
resonance
where as you are thinking in terms of anti resonance which portends to
a higher impedance and also the condition of equilibrium.

I apologize if I gave you that idea, Art. I am talking
about a physically short (38 degrees), electrically 1/4WL
(90 degrees) *resonant* antenna over mininec ground. The
feedpoint impedance is low and resistive.

In the example given, the stinger supplies 19 degrees
of phase shift, the base-loading coil supplies 19 degrees
of phase shift, and the impedance discontinuity between
the coil and the stinger provides a point phase shift that
makes up the difference between 38 degrees and 90 degrees.

As I hammer away at this concept, I am wondering if a
loaded mobile antenna can be optimized if only the correct
model is adopted. Is a high-Q loading-coil always better
than a loading-coil with a lower Q? Are fat/short loading-
coils always better than skinny/long loading-coils? Some
field measurements have cast doubt on some long-held
concepts.

But obviously the question cannot be answered as long as
some people insist on using the lumped circuit model for
the loading coil, e.g. virtually zero delay through the
coil.

I have measured the delay through a 75m bugcatcher coil.
It was approximately 25 nS, a magnitude greater than
w8ji's "measurements". It doesn't matter if my measurements
were off by 20%. The magnitude difference between my
measurements and w8ji's "measurements" is too significant
to be ignored.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Loading coils: was Dish reflector
 

Roy Lewallen wrote:

A single conductor doesn't have a characteristic impedance -- it's the
impedance between the two conductors of a transmission line. You can
measure a characteristic impedance between, say, a coil and ground, but
its value depends on the spacing between the two. If the coil is tilted
with respect to the ground, the impedance of this two-conductor system
will change with the position along the coil.

Roy: I understand what you are saying. But the derivation of
Characteristic Impedance in the Corum Bros. paper depends only on the
coil dimensions and number of turns; it is independent of any
relationship to other conductors or groundplanes. I also note that
ON4AA's inductance calculator predicts the "Characteristic impedance
of n=0 sheath helix waveguide mode at design frequency" based purely
on the coil geometry. The maths is a bit beyond me (trying to solve
Maxwell's equations for a solenoidal helix), but seems to bear analogy
to the derivation of the characteristic impedance of a waveguide.

I'm inclined to try to understand it better, because it's this derived
Characteristic Impedance, along with the axial Velocity Factor, that
generates the reactance values which seem such a good match to
experimental and modelled results.

Regards,
Steve G3TXQ

Loading coils: was Dish reflector
 

steveeh131047 wrote:
I'm inclined to try to understand it better, because it's this derived
Characteristic Impedance, along with the axial Velocity Factor, that
generates the reactance values which seem such a good match to
experimental and modeled results.

Steve, you will find some old-fashioned concepts here
based on the lumped-circuit model rather than the
distributed network EM wave reflection model. One can
easily disprove the assertion that a single wire
in free space doesn't have a characteristic impedance
by asking the question: Does a single electromagnetic
wave traveling through free space (without a wire)
encounter a characteristic impedance? If so, why doesn't
a single wave traveling through a wire in free space
encounter a characteristic impedance? Of course, the
ratio of the electric field to the magnetic field,
whatever that turns out to be, is the characteristic
impedance of a single wire in free space. It, like
the characteristic impedance of free space, seems
to be a few hundred ohms.

There are lots of old wives tales asserted by the gurus
on this newsgroup. One must be careful what one accepts
as technical fact.

"A single conductor doesn't have a characteristic impedance."
is a preposterous assertion. If free space itself has a
characteristic impedance, what are the chances that a
single wire in free space would not have a characteristic
impedance??? Zero, at best??? :-)

Some will say: "Where is the return path for the current?"
I will respond: Where is the return path for the "current"
arriving from the Sun that can be captured by a solar
panel? Good Grief!
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Loading coils: was Dish reflector
 

On Apr 23, 3:21*pm, Cecil Moore wrote:

I have measured the delay through a 75m bugcatcher coil.
It was approximately 25 nS, a magnitude greater than
w8ji's "measurements". It doesn't matter if my measurements
were off by 20%. The magnitude difference between my
measurements and w8ji's "measurements" is too significant
to be ignored.

Cecil: that's a very significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros. paper it predicts an
axial Velocity Factor of 0.33. That would equate to a delay across the
10" long coil of 24.7nS !!!!!

Regards,
Steve G3TXQ

Loading coils: was Dish reflector
 

On Apr 23, 3:21*pm, Cecil Moore wrote:
I have measured the delay through a 75m bugcatcher coil.
It was approximately 25 nS, a magnitude greater than
w8ji's "measurements". It doesn't matter if my measurements
were off by 20%. The magnitude difference between my
measurements and w8ji's "measurements" is too significant
to be ignored.

Cecil: that's a VERY significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros paper it predicts an
axial Velocity Factor of 0.033. That would equate to a time delay of
24.7nS across the 10" long coil !!!!

Regards,
Steve G3TXQ

Loading coils: was Dish reflector
 

steveeh131047 wrote:
On Apr 23, 3:21 pm, Cecil Moore wrote:
I have measured the delay through a 75m bugcatcher coil.
It was approximately 25 nS, a magnitude greater than
w8ji's "measurements". It doesn't matter if my measurements
were off by 20%. The magnitude difference between my
measurements and w8ji's "measurements" is too significant
to be ignored.

Cecil: that's a very significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros. paper it predicts an
axial Velocity Factor of 0.33. That would equate to a delay across the
10" long coil of 24.7nS !!!!!

Of course, you mean *0.033* for the VF of w8ji's coil which
was 10tpi, 100turn, 2" dia.

10"/12/0.033 = 25 feet equivalent to straight wire.

The VF of my Texas Bugcatcher coil is 0.02. It has 4tpi,
26turn, 6" dia.

6"/12/0.02 = 25 feet equivalent to straight wire.

These two coils have essentially equal delays at 4 MHz.
They are each very close to 0.1WL, i.e. 36 degrees.

The delay for one wavelength at 4 MHz is 250.5 nS so
each coil would have a delay of 1/10 that value or
25 nS. Everything fits the model.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com