Circular polarization... does it have to be synchronous??
 

John:

[snip]
I think investing some time with this math (it's not all that difficult)
[snip]

Agreed!

[snip]
will provide one with insight into the concept of polarization and perhaps
head off some misconception. If anyone is interested and has Mathcad,
I've got a worksheet that allows one to vary these parameters, plots the
resulting ellipse (or circle or line) and also calculates ellipticity
(axial ratio) and eccentricity. Sincerely, and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337
[snip]

Thanks John!

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

Dave:

[snip]
"Dave" wrote in message
...
J. B. Wood wrote:

I think investing some time with this math (it's not all that difficult)
will provide one with insight into the concept of polarization and
perhaps
head off some misconception. If anyone is interested and has Mathcad,
I've got a worksheet that allows one to vary these parameters, plots the
resulting ellipse (or circle or line) and also calculates ellipticity
(axial ratio) and eccentricity. Sincerely, and 73s from N4GGO,

All I have to know is that Circular Polarization always helps when one end
of the path is prone to random polarizations, even with the 3 dB power
loss.
[snip]

Yep, CP is good!

No matter how it is generated...

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

[snip]
A patch antenna, circularly polarized, mounted at the end of a
motor shaft, rotating in the opposite direction of the polarization...
.... at a speed equal to the frequency...

Does the polarization "unravel" and emit a linear, non-rotating
polarization ?
[snip]

Ype that's exactly what would happen!

[snip]
Is this the sort of principle that you were trying to convey ??
[snip]

Yeah, you've got it man!

[snip]
If this is the case, any discrepancy in the motor, say 1 hz out of
10 Mhz , would result in an Efield rotating at a 1 hz rate.... and
the
receiving antenna would have to be very very very long in order
to fully receive the polarized wave....... I think....

And if the motor shaft and the frequency were identical, the Efield
would be linear, stable, and non-rotating.....
[snip]

I can see that you did not find that so hard to "grok". Good work man!
Thanks!

[snip]
This is getting beyond my personal antenna expertise, but I still find
it
interesting....... Please pardon my lack of understanding, .... if I
[snip]

Andy! No problem you have it... there is no lack on your part.
Fortunately
you do not seem to be encumbered by convention. Your understanding is
"right on"!

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

Roy:

[snip]
"Roy Lewallen" wrote in message
treetonline...
Something just occurred to me. I did get to thinking.

My previous answers were wrong.
[snip]

Yep, I thought as much...

[snip]
Peter's spinning antenna wouldn't produce a circularly polarized wave (as
universally defined) even if it was synchronous with the wave frequency.
As I've said, a circularly polarized wave has constant E field amplitude;
Peter's wave would have a time-varying amplitude. If it were synchronous,
the nulls and peaks would always occur at the same places in the rotation
cycle, so they would occur at fixed angles relative to a rotational
reference point. If non-synchronous, the nulls and peaks would rotate at
the beat frequency.
[snip]

The problem is... that most "conventional" code and theory, e.g. NEC
does not allow for antennas in motion. These theories and computer
codes/algorithms are based upon a static steady state solution of the
Maxwell/Heaviside equations... i.e. E is a "fixed" phasor rather than
an oscilating waveform.

[snip]
It seems to me that the way to mechanically generate a circularly
polarized wave would be to rotate a source of *static* E field, for
example, a short dipole with constant applied DC voltage at the feedpoint.
[snip]

Hmmm... restricting that dipole to a "static" source is really far too
restrictive. This assumption likely results from the assumption
that E is a sinusoidal steady state value rather than a dynamic
(transient) wave.

[snip]
That should produce a circularly polarized wave with the frequency being
the rotational frequency of the dipole. At any point in space, the E field
would change with time, and would propagate, and it would look exactly
like a circularly polarized wave broadside to the rotation plane.
[snip]

Yes, but E is not "fixed" in time, it is the magnitude of an oscillating
phasor!

A DC phasor would not propagate. Of course!

[snip]
If the scheme works and radiation is occurring, then power must be going
into the antenna, which in turn means it's drawing current that's in phase
with the applied voltage. When stopped, no current will flow, but when
rotating, it does. So how does the antenna know it's rotating? How about
this -- if you instantaneously move the antenna into some position, a
static E field appears there, and propagates outward at the speed of
light. Closer in than the leading edge of the propagating wave, the field
is static. When we rotate the dipole to a new position, it moves through
the field from its previous position, which induces a current in it. Hence
the current. It's fundamentally a generator, with the field being in the
air.
[snip]

Yes that would be the case if the rotating antenna was excited with DC,
however that is not necessarily the general case.

In general the "center" frequency or "carrier" frequency may be any
arbitrary frequency, down to and including DC. Maxwell's/Heaviside's
equations hold for all frequencies from zero (DC) to infinity.

[snip]
I'd be willing to bet a moderate sum that if you did apply a DC voltage to
a dipole and rotated it, you'd see an alternating current with a frequency
equal to the frequency of rotation, and a circularly polarized wave
broadside to the antenna.
[snip]

Wow! Roy.... you are taking a big risk here. What is the (exact) value of
that
"sum"?

[snip]
I suspect that the current and the radiated field increase in amplitude
with rotational speed, so you might have to get it going really fast
before you can detect the effects.

Now there's some food for thought.

Roy Lewallen, W7EL
[snip]

Agreed! Hey... not many are able to "think outside the envelope", but I
do believe we are getting to the edge...

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

[snip]
"christofire" wrote in message
...
..
..
..
A source of endless coffee-time debates where I used to work! No, the
current into the rotating dipole would be DC and the means of rotation at
the radio frequency would take the place of the 'transmitter'. If the
current were alternating then the radiated electric field would be
discontinuous but it isn't; it has constant magnitude. Between two such
systems separated by many wavelengths, if there were no anisotropic
material around, reciprocity would apply and a means of conveying DC by
radio would be created!
[snip]

Perhaps, but.... the intersting case is when the "center" frequency is
somewhat
higher than DC.

[snip]
However, intriguing and amusing as this analogy might be I wonder if it
really has any practical value.
[snip]

T. J. Watson, the early CEO of IBM is reputed to have stated, "I see no real
requirement for more than 7-10 computers in this world!"

[snip]
For real mechanical rotating parts the frequency would be limited to
something rather low like the tens of kHz at which Alexanderson
alternators work, and then the wavelength would be so long that it would
probably be impossible to construct an efficient radiator*. The quickest
moving antenna I've encountered was a commutated plasma antenna, using a
construction similar to a 'dekatron' tube, but even then the length of the
radiator was so small that SHF would be needed to achieve worthwhile
radiation efficiency* and the maximum commutation speed was limited to a
few MHz by the time it takes to establish the plasma at each step in the
commutation cycle.
[snip]

What if you could electronically rotate antennas at any desried
(practically) high frequency?
Consider, for example phased arrays driven through elecronically controlled
phase shift
networks. Would that work?

[snip]
*(Of course, the conventional principles of radiation resistance vs. loss
resistance may need 'massaging' to bring them into line with the concept
of creating transverse waves by rotating a dipole connected to a battery!)
[snip]

Rotating dipoles do not have to (only) be connected to batteries. They
could
be connected to signal generators operating at 3.765MHz, no?

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

[snip]
Hi Chris

I am not smart enough to analyze the effects of rotating a dipole with DC
applied to it, but I have doubts that it would create a "far field". Did
you guys ever figure out how the "DC dipole" generates a Far Field?

Jerry KD6JDJ
[snip]

Jerry... no one on this thread, except perhaps Roy, has restricted the
"frequency" of
the signal applied to said mechanically rotating dipole to be zero, f = 0!!
In fact, in principle,
the frequency of the signal applied to the rotating dipole could be any
desired frequency
selected from the frequency range minus infiinty to plus infinity.

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

Roy:

[snip]
"Roy Lewallen" wrote in message
...
Jerry wrote:
..
..
..
The whole thing is just a mental exercise to help gain a better
understanding of the nature of a circularly polarized field.

Roy Lewallen, W7EL
[snip]

I agree that it is an exercise to help gain a better understanding of
circular polarization, but...

It is not just a "mental" exercise.

I believe that hhere are practical applications of this phenomena!

FWIW....

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

Jerry:

[snip]
I will respectfully submit that a car alternator doesnt so much spin a
magmetic field as it Rotates the field past a conductor. A car
alternator is a lumpy magnetic field that is spun past stationary coils of
wire. There is no misunderstanding about inductive coupling of close by
conductors. My question related to far field "radiation". I am aware
that my understanding of far Field radiation is very limited, so i dont
propose that i have answers. I do have question about generating a far
field by spinning a DC excited dipole.

Jerry KD6JDJ
[snip]

There are many practical examples extant of such "rotating" fields...

Consider the rotating field generated within the stator of a "shaded pole"
electric motor, or perhaps
the roing field of a synchronous electric motor.

However the rotating electromagntic fields of AC electric motors have
conventionally been
synchronized with the frequency (60Hz in North America) of the exciting
waveform. That
commercial application does not preclude applications wherein the rotating
field of an AC
motor is not synchronous with the exciting prime mover. For example,
imagine a motor
wherein the stator magnets are rotated by a separate mechanical device,
bicycle pedals?,
that pulls the rotor around at a frequency not synchronized with the stator
prime mover
excitation. Just because there is no real commerciall application for such
a motor in
today's markets, does not mean that such is not useful for some other
purpose.

Open minds create new applications

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

Jerry:

[snip]
Tell me, did you guys ever decide that there would be a far field
generated by the spinning dipole with DC on it? I dont refer to the
inductive field.
Maybe there is no way to separate Far Field from any condition where an
inductive field is generated.

Jerry KD6JDJ
[snip]

If the answer for DC was no, then....

What is your answer for a spinning dipole with 0.0001Hz on it, or say 1,
000, 003.33333 Hz on it?

Food for thought?

-- Pete K1PO

Circular polarization... does it have to be synchronous??
 

Jerry:

[snip]
"Jerry" wrote in message
...
..
..
..
Yeah, I never ascribed any practical use to the "CP by spinning". But,
there are some fundamentally good thoughts generated here. For instance,
I can easily see why two dipoles rotating at the same rate and rotational
direction will couple *nothing*. Thats like trying to receive RHCP with
a LHCP antenna.
I have lived a long time without understanding Poynting and Maxwell
(almost 100 years older than me), I wouldnt want to change that now.

Jerry KD6JDJ
[snip]

Hey, the shareholders in the pony express company never ascribed any
practical use to the internal combustion engine...

-- Pete K1PO