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Author Topic: Helical Antennae: RHCP/LHCP  (Read 8089 times)

Henry Cohen

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Re: Helical Antennae: RHCP/LHCP
« Reply #10 on: November 19, 2015, 04:28:59 pm »

Big W's Roadside BBQ in Wingdale NY. I've already dragged Pete there, he cam away a believer.

Will have to put that on my itinerary. Have you been to Round Up in Cold Spring on Rt 9? Very good.
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Henry Cohen

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Pete Erskine

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Re: Helical Antennae: RHCP/LHCP
« Reply #11 on: November 19, 2015, 10:20:25 pm »

Will have to put that on my itinerary. Have you been to Round Up in Cold Spring on Rt 9? Very good.


Lets have a RF get together everyone this weekend!  I've often wondered if LH Brisket is as good as RH and when you should eat each.
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Mac Kerr

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Re: Helical BBQ: RHCP/LHCP
« Reply #12 on: November 19, 2015, 10:45:50 pm »

Lets have a RF get together everyone this weekend!  I've often wondered if LH Brisket is as good as RH and when you should eat each.

I'm up for it any time. Big W's is my favorite, but I'll try a new joint. Round Up is not far from Riverview in Cold Spring.

Mac
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Henry Cohen

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Re: Helical BBQ: RHCP/LHCP
« Reply #13 on: November 20, 2015, 01:08:59 pm »

I'm up for it any time. Big W's is my favorite, but I'll try a new joint. Round Up is not far from Riverview in Cold Spring.

Ditto. Of course Big W is the new place for me, so you guys pick it.

LH vs. RH brisket is moot: The mouth is linearly polarized  :)
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Henry Cohen

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Lyle Williams

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Re: Helical Antennae: RHCP/LHCP
« Reply #14 on: November 20, 2015, 01:36:56 pm »

Generally on a fixed link linear polarity is fine.  The main benefit of circular polarity is that a linear polarity antenna at the far end of the circuit can move around at different angles without causing deep fades due to crossed polarity.  In audio I generally see the same objective persued through diversity reception on two linear polarity antennas.

A bit of trivia - one application for crossed-handedness in circular polarisation is when your signal is to be reflected off an object.  The transmitted signal might start as LHCP but after reflection it becomes RHCP.
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Henry Cohen

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Re: Helical Antennae: RHCP/LHCP
« Reply #15 on: November 20, 2015, 02:45:38 pm »

A bit of trivia - one application for crossed-handedness in circular polarisation is when your signal is to be reflected off an object.  The transmitted signal might start as LHCP but after reflection it becomes RHCP.

A common misconception. Whereas a linear polarized electromagnetic wave is subject to negligible shifts in polarization when reflected, circular (actually elliptical) polarizations are not. In both cases it's the phase of the signal that has changed significantly.

Think of light: If a light with a polarizing filter is shined at an optically neutral mirror, the reflected light remains the same color(s), it's just getting to your eye a few attoseconds later.
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Henry Cohen

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Lyle Williams

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Re: Helical Antennae: RHCP/LHCP
« Reply #16 on: November 20, 2015, 10:48:09 pm »

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Henry Cohen

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Re: Helical Antennae: RHCP/LHCP
« Reply #17 on: November 21, 2015, 04:46:06 pm »

https://en.m.wikipedia.org/wiki/Circular_polarization#Reversal_of_Handedness_by_Reflection

Granted, the effect depends on the angle on incidence.

If you read the description carefully;
"Upon such reflection, the rotation of the plane of polarization of the reflected light is identical to that of the incident field. However with propagation now in the opposite direction, the same rotation direction that would be described as 'right handed' for the incident beam, is 'left-handed' for propagation in the reverse direction, and vice versa",  it says the reflected wave does in fact have the same handedness as the incident wave, it's just that because the observer remains in the same position, the rotation as observed is opposite, and that's true. But that's not how handedness is determined: It's determined by standing behind the wave front as it moves away from the observer. So if the the wave is reflected, the observer must now move and stand behind the wave as it travels away from the reflecting surface.
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Henry Cohen

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Lyle Williams

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Re: Helical Antennae: RHCP/LHCP
« Reply #18 on: November 22, 2015, 03:04:40 pm »

Consider this example.  Viewed from the transmitting source an outbound RHCP has a clockwise spin. 

(Holding your right hand with the thumb in the outbound direction of propagation, with fingers following the clockwise rotation of the plane of polarisation.)

-

Upon reflection, still viewed from the transmitting source the returning signal still has a clockwise spin.  But that's now LHCP due to the direction change.

(Holding your left hand with the thumb in the inbound direction of propagation, with fingers following the clockwise rotation of the plane of polarisation.)
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Mac Kerr

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Re: Helical BBQ: RHCP/LHCP
« Reply #19 on: November 22, 2015, 06:02:32 pm »

Ditto. Of course Big W is the new place for me, so you guys pick it.

LH vs. RH brisket is moot: The mouth is linearly polarized  :)

All that food in front of Henry is what he ordered. That would be the combo for 2, Pete and I were 1 tray each. Love Big W's.

Mac

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