On 17 Jul 2004 13:27:03 -0700, (J. Harvey) wrote:
One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. DBS satellites (for example) use
RHCP and LHCP to double their bandwidth, just like FSS satellites use
H and V. I have not heard anything about the DBS RHCP transponder
having to worry about the LHCP transponder. I haven't heard any
mention of nulls suddenly appearing and disappearing in the downlink

That is because the nulls occur orthogonally to (and not along) the
path. ... At least in the sense of your thought-experiment.

passband as the two senses happen to coincide, out of phase. I haven't
heard about the CP being converted to linear and causing interference
(at -3dB) in the other CP mode.

And possibly for a very good reason: the earth is thousands of miles
away where the subtended arc of the service region precludes more than
a few degrees difference in path length/delay. The initial phase
balance is preserved by geometry.

If they cancel out, then where does the energy go? Make it a mega-watt
each and follow the smoke. If they combine in the vacuum of space,
where is the smoke?

Hi Jeff,

This is just a tarted up version of the multipath phenomenon otherwise
called the Fresnel Zone which, in turn is an example of the optics
display of Newton's rings. If the earth were flat (a presumption of
modelers), then you would observe concentric rings around the service
area that were alternately hot then cold. The earth isn't flat, but
that doesn't cast this effect into the unfathomable, it simple
distorts the progressively outer rings' widths.

73's
Richard Clark, KB7QHC

On Sat, 17 Jul 2004 14:26:54 -0700, Roy Lewallen wrote:

J. Harvey wrote:

One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. . .

Some time ago, I stated that at any point in space there's a single
field, and that we can split it into various components to suit our
analytical needs. But the way we choose to split it or, conversely, the
way it was created (from a single source or polarization, or multiple
ones) doesn't alter the nature of the field in any way. I'm not sure if
what I said was simply disbelieved or whether it was ignored -- the end
result is the same.

The total field you get from simultaneous RHCP and LHCP waves is simple
to see by using the index finger of each hand to represent the
instantaneous orientation of the E field from each of two waves. Point
the index finger of your left hand downward and the index finger of your
right hand upward, knuckle-to-knuckle, so the fingers make a vertical
line extending from one fingertip to the other. The left index finger
will represent the LHCP wave and the right index finger the RHCP wave.
At the beginning instant that we're illustrating, they're out of phase
and sum to zero. So the field at that point and that time is zero.

Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the left, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the left, and the sum is a horizontal field with magnitude equal to 2
fingers. If you continue this process, you'll find that the sum of the
two fields is always horizontal, and it oscillates between zero and two
fingers in instantaneous amplitude. It is, in fact, exactly the same as
and entirely indistinguishable from a horizontally polarized wave coming
from, say, a dipole. You can reach the same conclusion mathematically
from the equations I posted a few weeks ago.

If you run the same experiment beginning with the fingers in phase --
both pointing upwards -- you'll get a purely vertically polarized wave.
And with other starting phase angles, you'll get linearly polarized
waves of other orientations.

No magical energy distruction or disappearing takes place -- it's all
accounted for. And you can receive it just fine with a dipole.

Roy Lewallen, W7EL

You're absolutely right, Roy, I confess I shot without aiming properly. It's
been many years since I worked with CP, and I now remember going through the
same exercise that you presented above with the same result, a
linearly-polarized wave. Thanks for the refresher course.

Walt, W2DU

On Sat, 17 Jul 2004 16:48:38 -0500, Cecil Moore wrote:

Roy Lewallen wrote:
If you run the same experiment beginning with the fingers in phase --
both pointing upwards -- you'll get a purely vertically polarized wave.

Actually, I got the same two fingers back on the freeway the other day. :-)

Cecil, you're lucky you got two back. I usually only get one.

Walt

Correction:

Roy Lewallen wrote:
. . .
Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the left, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the left, and the sum is a horizontal field with magnitude equal to 2
fingers. . . .

My rotation was reversed -- it should read:

Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the *right*, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the *right*, and the sum is a horizontal field with magnitude equal to 2
fingers. . . .

The conclusion isn't affected by the error.

Roy Lewallen, W7EL

"Walter Maxwell" wrote in message
...
On Sat, 17 Jul 2004 18:11:39 -0000, "Dave" wrote:

good idea, they are just another way for lawyers to make money. any new
idea gets ripped off as soon as its out anyway with cheap imitations...
and
then lawyers make more money suing the infringers if they can get a hand
on
them.

wrote in message
news
On Sat, 17 Jul 2004 12:11:22 -0000, "Dave" wrote:


"J. Harvey" wrote in message
. com...

Any comments or technical objections?

if this were that obvious to you, and it would work as described, it
would
already be in wide use.

So let's save some federal money by shutting down the USPTO.
Everything useful that works has already been thought of, so there's
no need for them any more.

i haven't had enough caffeine yet to explain why,
but somehow i think you would get complete cancellation and there
would
be
no propagation at all.

Without giving the problem any serious mathematical or physical thought,
only
knee-jerk intuition, IMO, if a radiator suitable for radiating CP of
either hand
were fed with equal signals leading to both RHCP and LHCP simultaneously,
I
agree with the poster above that complete cancelation would result, and
there
would be no radiation.

This is why a linearly-polarized antenna could not receive any energy.
(har har)

Walt, W2DU

Walter

I'm not bright enough to fully understand all this discussion. But, I
wonder if the appropriate phasing of two circularly polarized waves, one
RHCP and the other LHCP can result in a linearly polarized wave, not zero.
I think I could build an antenna from two crossed dipoles spaced 1/4 wave
apart that porduce either RHCP or LHCP radiation depending on how *one* of
the dipoles is phased with respect to the other. Feed them in phase and get
RHCP. Change the phase of either dipole 180 degrees and get LHCP. The
"unchanged" dipole in both cases has the same polarization and phase.

If (theoretically) two of these antennas were superimposed on each other,
only the phase of *one* dipole of each antenna needs to be 'reversed' to
produce the 'reversed' (RH or LH) polarized wave. The other dipole of each
antenna can be in phase with each other, so the sum is a linear wave.

What am I missing??

Jerry

On Sun, 18 Jul 2004 15:44:09 GMT, "Jerry Martes" wrote:


Without giving the problem any serious mathematical or physical thought,
only
knee-jerk intuition, IMO, if a radiator suitable for radiating CP of
either hand
were fed with equal signals leading to both RHCP and LHCP simultaneously,
I
agree with the poster above that complete cancelation would result, and
there
would be no radiation.

This is why a linearly-polarized antenna could not receive any energy.
(har har)

Walt, W2DU

Walter

I'm not bright enough to fully understand all this discussion. But, I
wonder if the appropriate phasing of two circularly polarized waves, one
RHCP and the other LHCP can result in a linearly polarized wave, not zero.
I think I could build an antenna from two crossed dipoles spaced 1/4 wave
apart that porduce either RHCP or LHCP radiation depending on how *one* of
the dipoles is phased with respect to the other. Feed them in phase and get
RHCP. Change the phase of either dipole 180 degrees and get LHCP. The
"unchanged" dipole in both cases has the same polarization and phase.

If (theoretically) two of these antennas were superimposed on each other,
only the phase of *one* dipole of each antenna needs to be 'reversed' to
produce the 'reversed' (RH or LH) polarized wave. The other dipole of each
antenna can be in phase with each other, so the sum is a linear wave.

What am I missing??

Jerry

Well, Jerry, your last statements is correct. Apparently you missed Roy's post,
where he explained that two equal harmonically related RHCP and LHCP signals
reduce to a linearly-polarized wave. I was out of my tree when I came up with
the knee-jerk response of no signal. I knew better, but I spoke without having
my brain in motion. Happens too often when one gets to my age.

Walt

Roy Lewallen
...
And you can receive it just
fine with a dipole.

Thanks Roy.

It now makes perfect sense to me that since CP can be generated with
two linear antennas (crossed dipoles, phased appropriately), it must
be true that one could make linear using two CP antennas - just as you
reminded us.

Still - I have a nagging feeling that, taking advantage of the -3dB
separation between CP and linear, there must be at least a small (3dB
SNR) Shannon window in there that might be used to squeeze through
some extra data. Likely not (yet) cost effective even it it does
exist.

I appreciate all the responses.

Now - what shall I do with the $10,000 that I didn't spend on a patent
?

;-)

J. Harvey wrote:
"Thanks Roy. It now makes perfect sense to me that CP can be generated
with two linear antennas (crossed dipoles, phased appropriately), it
must be true that one could make linear using two CP antennas - just as
you reminded us."

That`s true according to J.D. Kraus, inventor of the helical antenna. On
page 477 of his 1950 book "Antennas":
"Elliptical Polarization as Produced by Two Circularly Polarized Waves -
When the amplitudes are equal, the resultant wave is linearly polarized
(Fig.15-28a)."

Best regards, Richard Harrison, KB5WZI