Peter O. Brackett wrote:
. . .
Yes indeed, we must be talking at cross purposes, since we seem to
have no disagreement on any of the above. I don't see where we differ
at all!

For starters, a circularly polarized wave, as universally understood,
has an E field which is constant in amplitude, rotates in synchronism
with the rotational frequency of the field, and has a particular
relationship to constituent linearly polarized components. The field
you're generating doesn't, yet you're calling it "circularly polarized".

[snip]
Would the rate of spin have to be 99-44/100 percent of the synchronous
frequency? Or would it have to be closer than that?

At what magic spin frequency would the two be indistinguisable.
[snip]

I would repeat the above question in a slightly different way...

How much frequency, or for that matter phase, difference must there
be between the mechanical spin frequency and the carrier frequency
before you could tell the difference between your "conventionally defined"
circular polarization and my definition?

Any difference at all. If there's even a tiny difference, the E field
will change in amplitude with time. If it's perfectly synchronous it
won't. The rate at which it changes with time is the difference between
the field rotation frequency and the frequency of the generated signal.
If they're synchronous, the difference is zero, and no change in
amplitude with time.

If my antenna was spining with an angular velocity within say,
0.000000000005% of the carrier frequency, would that do it?

If by "it" you mean make the difference non-discernible, the answer is
no. See above.

Or perhaps my spin rate would have to be closer to the carrier
frequency than that?

See above.

If so, then how close does it have to be to qualify to be called
circular polarization under (your) traditional/conventional
definition?

They have to be identical. See above.

The question you posed earlier was different, involving detection of the
difference with a particular kind of antenna. Like the linear antenna
you used in another example, it filters the signal which alters its
properties. So my answer to this new question is different.

[snip]
What you'll end up with is amplitude modulation with the modulating
frequency being the beat note between your spinning speed and the wave
frequency. This creates sidebands. You'll see this when the sidebands
are within the bandwidth of the helix. Outside that, the helix will
filter off the sidebands and you'll just see the "carrier" -- the
original wave with no modulation.
[snip]

Hmmm... Yes, I agree and that's partially correct, but some of the above
paragraph is
somewhat "fuzzy" to say the least.

That helix must be a very sharp [brick wall???] filter, no?

No.

Let's get real here, no practical implementation of any kind of physical
filtering
mechanism can filter with infinitely sharp transition bands. It just
doesn't happen
in nature.

That's not required, although I see it's how you've interpreted my use
of "bandwidth". There is no such brick wall rejection region.

[snip]
Here's a really neat little trick you might want to add to your bag --
superposition. As I mentioned, you can create a circularly polarized
wave from two linearly polarized waves. The linearly polarized waves
are of course normally time-varying. As long as the propagation medium
is linear (such as air), superposition says you can split the
circularly polarized wave apart into two linearly polarized waves,
study and analyze how they propagate, then add the two components back
together again after the propagation. This is, incidentally, a very
simple way to see what happens when a circularly polarized wave
reflects from a surface -- analyze the linear components separately
and add the results.
[snip]

Heh, heh... Superposition is not a 'trick' it is a well known principle and
Roy, I agree with all of the above!

What's your point?

You don't believe that a wave with constant amplitude E field can
propagate. My point is that the constant E field amplitude circularly
polarized wave can be made of the sum of two time-varying waves. Each of
these waves can propagate. If you're familiar with superposition it
should be obvious that the original wave can be split into those
components, each component and its propagation can be analyzed
separately, and the results summed at the far end of the path. That's
how a CP wave having a constant amplitude can propagate.

Bringing up superposition is fine, but you seem to raise the concept of
superposition simply as a digression here, not as a means of disproving my
assertion that mechanically spinning a linear antenna is tantamount to
conventional circular polarization.

No, it was brought up to demonstrate how a wave having a constant
amplitude E field can propagate. You had used the argument that a
circularly polarized wave can't propagate because its E field has a
constant amplitude, as support for your incorrect assertion that the
amplitude of the E field of a circularly polarized varies with time. A
circularly polarized wave has a constant amplitude E field, which can be
easily demonstrated from the equations describing it. It propagates.
Your pseudo-circularly polarized wave doesn't have a constant amplitude
E field, which is only one way it differs from a circularly polarized wave.

[snip]
That's about all I can do at this end. I can't make you actually pick
up a text and learn about circularly polarized waves, and until you
do, you'll have some fundamental misconceptions about them.
[snip]

Hmmm... that was a cheap shot! Unfortunately I agree, YOU cannot
make me pick up a text.

However, I can make myself do so myself, and... it may (or may not)
interest you to know that I have done so on many occasions.

In fact I have picked up several such texts, addressing such subject matter
authored by Physicists and Engineers ranging over subjects
as diverse as radio frequency antennas and optics.

Would it impress you if I sent you a picture of my personal library
of several hundred volumes, which contains perhaps a dozen or more
textbooks on electromagnetics. Since I have been examined on these
subjects at graduate degree levels by the faculty at several duly
accredited
Universities it seems that there is some evidence that I may have read and
understood at least a few paragraphs from those texts that I "picked
up"! [smile]

I'm impressed, but it's not apparent to me why, with those resources
available, you're having trouble finding how the amplitude of the
circularly polarized wave E field varies with time, or applying
superposition to discover how it propagates. Choose one or two of your
texts which has the equations for circularly polarized waves. Chances
are good that I have the same text, and if you'd like I can show you how
to derive the instantaneous E field amplitude from the equations. But
I'm afraid you would have to pick it up to find the equations.

But if you can do that, you might be able to write the equations
describing your signal, and then the differences between it and the CP
equations should become obvious.


[snip]
Guess I'm one of those folks who someone described recently as "having
the common sense educated out of me". It's served me well, since it's
enabled me able to spend a career designing a wide variety of state of
the art electronic circuits and antennas, successfully mass produced,
which work as designed. But I know it's not for everyone.
[snip]

Hmmm... I too have spent (wasted?) most of several decades designing
electronic products and equipment for international markets sold in more
than 40 countries with at total sales volume exceeding $5BB dollars.

And it seems in today's world that if you combine that Engineering
experience with $2.50 you can buy a cup of coffee at Starbucks!

Now that we have suitably set the stage, lets get back to the common
sense Engineering question at hand!

All I need is a number!

Oh, if that's all you need, 42 is always a good choice.

Perhaps I should regurgitate the statement of Lord Kelvin about knowledge
that dear departed Reg used to quote. You know... the one about
quantifying
things, the one that says you know nothing unless you can put a number
to it!

Do I really need to do that here? Reggie dear friend, are you watching
from above?

Roy, please answer the following common sense Engineering questions, just
how close must the angular velocity of my spinning antenna be to the
carrier
frequency before YOU will allow it to be called circular polarization?

It must be exactly the same.

A simple numerical value in percentage form would do fine!

0.