Dish reflector
 

On Apr 20, 4:07*pm, Cecil Moore wrote:
Art Unwin wrote:
Kraus states that for a helix one should not use wire shorter than two
wavelength which I suspect is a substitute calculation for the VF
change from a straight radiator.

Because of adjacent coil coupling, it takes
more wire to achieve the phase shift effect
of a straight wire.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Which is what I have always maintained, lumped loads are not included
in Maxwell's
equations .
Art

Dish reflector
 

"Art Unwin" wrote in message
...
Which is what I have always maintained, lumped loads are not included
in Maxwell's equations .

CORRECT! he got one right! must be dumb luck.

you are absolutely correct, there are no terms in maxwell's equations
representing lumped loads. HOWEVER, you can use maxwell's equations to
derive the fields that explain how lumped elements work.

Dish reflector
 

On Apr 20, 6:06*pm, "Dave" wrote:
"Art Unwin" wrote in message

...

Which is what I have always maintained, lumped loads are not included
in Maxwell's equations .

CORRECT! *he got one right! *must be dumb luck.

you are absolutely correct, there are no terms in maxwell's equations
representing lumped loads. *HOWEVER, you can use maxwell's equations to
derive the fields that explain how lumped elements work.

At the expense of efficiency per unit length

Dish reflector
 

Cecil Moore wrote:
Tom Donaly wrote:
I don't blame him for plonking you. You're saying that because you
fantasized that Roy would make a mistake that Roy would never make,
that he also made the same mistake when measuring the delay through a
coil.

Sorry Tom, that is a diversion. The subject is NOT the delay
through a coil. The present subject is the delay through a
straight wire which is well understood. Please deal with the
topic at hand. If you refuse, we will know that you are not
sincere as far as technical facts are concerned.

Please ask Roy to prove that the current on a standing wave
antenna can be used to measure the delay through a straight
piece of wire that is x degrees long. If so, exactly how is
it done?

Roy is NOT omniscient. He definitely made the mistake but
like most gurus, refuses to admit it. You want to sweep the
mistake under the rug through diversions but I won't allow
you to do that. Once you and Roy admit that the current on
a standing wave antenna cannot be used to calculate delay,
everything else will become clear.

Please feel free to contact Roy by private email to resolve
the issue. Roy has, so far, simply stuck his head in the
sandbags and refused to respond. I'm sure he would have
advised you to plonk me instead of engaging me, for fear
of being proved wrong.

Yet, he admitted years ago that the phase of current in a
standing wave antenna varies by a very small amount. He
is presently trying to have his cake and eat it too. In
the process, he (and you as a supporter) are hoodwinking
the unwashed masses. Shame on all of you.

No, it's not a diversion. You're making up things in your head.
The original controversy involved a claim by you that the coil in
a short, mobile antenna made up for the degrees lost in said
shortened antenna. You were wrong. Now you've changed the subject to
a half wave dipole, attributing to Roy a position he would never take.
That's an old, stupid trick a woman might use in a domestic argument,
but it won't work here. I know you have a pathological need to
win every argument (you ought to talk that over with your analyst) but
that's no reason anyone should waste time agreeing with you.
73,
Tom Donaly, KA6RUH

Dish reflector
 

Cecil Moore wrote:

Roy is NOT omniscient. He definitely made the mistake but
like most gurus, refuses to admit it. You want to sweep the
mistake under the rug through diversions but I won't allow
you to do that.

Roy has, so far, simply stuck his head in the
sandbags and refused to respond.

He
is presently trying to have his cake and eat it too. In
the process, he (and you as a supporter) are hoodwinking
the unwashed masses. Shame on all of you.

Anybody get the feeling that Cecil and Art might be the same guy? :-)

http://www.8notes.com/school/riffs/c..._and_hardy.asp

ac6xg

Dish reflector
 

Art Unwin wrote:
I made a helical end fed antenna that is inside a cone shaped
reflector
The reflector is made from 1/2" mesh steel with an aluminum foil liner
and connected to the braid of the feed coax. No baluns are used, just
direct connections.
I was surprised to hear signals from the rear!
I thought that a dish reflector prevented such signals getting to the
receiver. So what can be wrong with the reflector or can signals get
reflected back from the frontal area? Antenna is at a 40 foot height
Any ideas as to what the fault could be?
Regards
Art
I have no experience with dishes thus the question Note, the helical
antenna does not protrude beyond the dish envelope.
Art

What's the relative size of "reflector" and helix? (i.e. is the
reflector in the near field of the helix, in which case, you could
easily have waves propagating along the surface of the reflector)

Dish reflector
 

On Apr 20, 7:16*pm, Jim Kelley wrote:
Cecil Moore wrote:

Roy is NOT omniscient. He definitely made the mistake but
like most gurus, refuses to admit it. You want to sweep the
mistake under the rug through diversions but I won't allow
you to do that.
Roy has, so far, simply stuck his head in the
sandbags and refused to respond.
He
is presently trying to have his cake and eat it too. In
the process, he (and you as a supporter) are hoodwinking
the unwashed masses. Shame on all of you.

Anybody get the feeling that Cecil and Art might be the same guy? *:-)

http://www.8notes.com/school/riffs/c..._and_hardy.asp

ac6xg

Very good but he rides a motor bike and I don't ride those vehicles of
death.
Cecil is correct tho, The lumped circuit represents the radiator
length times the velocity factor plus a fudge factor for being a
lumped load.
Art

Dish reflector
 

On Apr 20, 7:28*pm, Jim Lux wrote:
Art Unwin wrote:
I made a helical end fed antenna that is inside a cone shaped
reflector
The reflector is made from 1/2" mesh steel with an aluminum foil liner
and connected to the braid of the feed coax. No baluns are used, just
direct connections.
*I was surprised to hear signals from the rear!
*I thought that a dish reflector prevented such signals getting to the
receiver. So what can be wrong with the reflector or can signals get
reflected back from the frontal area? Antenna is at a 40 foot height
Any ideas as to what the fault could be?
Regards
Art
I have no experience with dishes thus the question Note, the helical
antenna does not protrude beyond the dish envelope.
Art

What's the relative size of "reflector" and helix? *(i.e. is the
reflector in the near field of the helix, in which case, you could
easily have waves propagating along the surface of the reflector)

The helix is four foot long and a foot diameter. The base of the
reflector is 1.5 feet
with a 45 degree angle. I have had the helix 0.5 feet shorter and 0.5
feet longer with similar results.On re examination of the antenn I now
see that the ground lead of the radiator is connected to the inside of
the reflector at a half way point and the coax
ground is connected at the base of the reflector. I think I will
change that ground connection to a common point.
Regards
Art

Loading coils: was Dish reflector
 

Tom Donaly wrote:

I'm going to break my reply up into two pieces. First I
will address the actual number of degrees occupied by
a loading coil.

No, it's not a diversion. You're making up things in your head.
The original controversy involved a claim by you that the coil in
a short, mobile antenna made up for the degrees lost in said
shortened antenna.

Sorry Tom, that is a false statement. Please stop misquoting
me. The coil occupies some number of degrees but not nearly
enough to make up for all of the "lost" degrees which are not
lost at all as I have demonstrated in the past and will do so
again here. Following is a *resonant open-circuit 1/4WL stub*
that is electrically 90 degrees long yet it is only physically
38 degrees long.

Z1
---19 deg 450 ohm feedline---+---19 deg 50 ohm feedline---open
-j145

The 450 ohm feedline occupies 19 degrees of the stub. The 50
ohm feedline occupies 19 degrees of the stub. The stub is
physically 38 degrees long total. It needs another 52 degrees
to make it electrically 1/4WL long and resonant. The "lost"
52 degrees is *not lost at all* and occurs abruptly at the
junction point '+'. Call the impedance at that point Z1. The
52 degrees of phase shift occurs between Z1/450 and Z1/50.
Microsmith says that Z1 = -j145.

Z1/450 = -j145/450 = -j0.3222

Z1/50 = -j145/50 = -j2.9

Take a look at the number of degrees between -j0.3222 and
-j2.9 on a Smith Chart. Surprise! There is the "lost" 52
degrees. Those degrees are not lost at all and are just
a fact of physics concerning phase shifts at an impedance
discontinuity.

Now if we multiply the stub impedances by 10, we have
a reasonable facsimile of a resonant base-loaded monopole.

19 deg coil
///////////////-----19 deg ~500 ohm stinger-----open
Z0= ~4500 ohms
VF= ~0.02

The loading coil occupies 19 degrees and the stinger
occupies 19 degrees. There is a 52 degree phase shift
at the coil to stinger junction. There are no "lost"
degrees. 19+52+19 = 90 degrees.

There were (are) two sides to the argument.

1. The coil furnishes the "lost" degrees.
FALSE!
The coil furnishes some number of degrees but not
nearly enough to make up for the phase shift at
the coil/stinger junction.

2. The coil supplies almost zero degrees.
FALSE!
The phase shift at the coil/stinger junction is not
enough to account for the "lost" degrees. The magnitude
of that phase shift is easily calculated on a Smith Chart.

Please skip the ad hominem attacks and use the laws
of physics and mathematics to prove me wrong.
--
73, Cecil, w5dxp.com

Dish reflector
 

Tom Donaly wrote:
You were wrong. Now you've changed the subject to
a half wave dipole, attributing to Roy a position he would never take.

On the contrary, Roy described his procedure in detail. I
then applied Roy's exact procedure to a 1/2WL dipole to see
if the procedure is valid for finding the delay through a
straight wire. Just as I suspected, the change in the phase
of the current is mostly unrelated to the number of degrees
in the antenna wire. Therefore, Roy's procedure is invalid and
cannot be used to measure the delay through a loading coil.

He made very accurate, very meaningless measurements - as did
w8ji. The primary current on a monopole, loaded or not, is of
the form I = Imax*cos(kx)*cos(wt). The amplitude is solely
a function of kx. The phase is solely a function of wt.
At any instant of time, the phase is the same all up and down
the wire including through the loading coil. Roy once verified
that is what EZNEC reports.

So the question remains: How did Roy use the current on a
standing-wave antenna, which doesn't change phase relative to
any other point on the entire antenna, to calculate the delay
through a loading coil or through a wire? The phase at the
bottom of the coil and the phase at the top of the coil are
always the same no matter what the delay through the coil.
Those phases are the same as the feedpoint phase and the phase
close to the tip top of the antenna within a very few degrees.

That's an old, stupid trick a woman might use in a domestic argument,
but it won't work here. I know you have a pathological need to
win every argument (you ought to talk that over with your analyst) but
that's no reason anyone should waste time agreeing with you.

Hurling ad hominem attacks will not help you in a technical
argument, Tom. Please use electronic theory and mathematics
to prove me wrong.

Will Rogers said, "Be sure you are right and then go on ahead."
I'm sure I am right.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com