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

[Franklin Antonio <antonio@xxxxxxxxxxxx>]

At 10:54 AM 11/1/2002, Ben wrote:
>The cause of my confused state is a picture found somewhere on the net
>that shows a man holding up a crossed yagi. In the picture the horizontal
>yagi is closest to him and the vertical one is 1/4 wave length ahead or in
>front of the horizontal one. The antennas are feed in phase.

Crossed Yagis are confusing.

 From the words you wrote above, it is IMPOSSIBLE to determine whether the 
polarization is right-hand or left-hand.

The problem is that even tho the two antennas are fed in-phase (meaning you 
have equal length cables after the splitter), there are still two ways that 
one can connect the cables.  If you flip the wires at the feed of one of 
these Yagis, you change the phase 180 degrees.  Now if that Yagi was 90 
degrees ahead of the other one due to its physical position, and you flip 
the phase of the drive 180 degrees by just flipping the wires, then it 
becomes 90 degrees behind instead of 90 degrees ahead, and the rotation 
goes the other way.

Therefore, to figure out the polarization of a crossed yagi, you need to 
know not only the physical offset of one Yagi vs the other, and the lengths 
of the feed cables, but also exactly which wire goes where on each driven 
element.

With many feed schemes, the driven element is fed from a coax, so the issue 
becomes which side of the driven element is connected to the center 
conductor.  (If you have some other kind of feed, perhaps a transformer 
balun, then you have to examine even more details.)

If you can see this detail in that web picture, then you can visually 
determine the polarization of the crossed Yagi.  If not, then you can't.


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