Re: [amsat-bb] Whose Right and Whose Left--CP REPLY

[Franklin Antonio <antonio@xxxxxxxxxxxx>]

At 02:26 PM 11/4/2002, Ben wrote:
>One of three things is going on.
>1. The picture is improperly defined
>2. The definition of Right and Left hand is backwards
>3. The cross yagi behaves differently than I understand

Its #3.  Thank you for providing a link to the picture.  Now we can see 
what you are talking about.  I agree with Howard's description.

> >http://www.g6lvb.com/images/rhcp.jpg,  If fed in phase the vertical
> > wavefront is received first and then the horizontal wavefront, thus
> > forming a right-hand screw.

To put it another way... There is a strong tendency to visualize a screw 
(helix) in space going thru the end of the two driven elements.  First thru 
the folded end of the horizontal driven element and then thru the folded 
end of the vertical driven element.  That would be a left handed screw of 
course.  However, that is not the right way to think about what happens to 
the FIELD.

The Horizontal driven element is BEHIND the vertical driven element, so 
that the horizontal field is DELAYED.  Therefore, if you observe what 
happens at one point in space along the boom, you see the crest of the 
vertical field, and then 90 degrees later see the crest of the horizontal 
field.  Looking at the picture, you can see that is right-handed 
rotation.  As you said, this agrees with the direction of the fingers of 
your right hand if your right thumb pointed in the direction of propagation.

This is very confusing.  I hope I managed to state the explanation without 
saying it backwards.  I reread it a couple of times in an attempt to make 
sure.  This is so hard to get right that in practice I've never tried to 
wire up a CP antenna to get the circularity "right".  I've always just 
flipped the polarization relay and used whichever setting "works".

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