[amsat-bb] RE: Seat (Set) me straight - CP

["Stacey E. Mills" <w4sm@xxxxxxxxxx>]

>It is my understanding that CP as defined by AMSAT is from the transmitters
>point of view. So if you stood behind a CP transmit antenna and could see
>the rotation of the signal as it left the antenna and if it were rotating CW
>than its right hand polarization. On the other hand if you were standing
>behind the satellite as it received the signal it would be rotating CCW. Its
>important for all parties to understand the entire definition. For instance
>in the world of commercial Satellite TV, where the ratio of receivers to
>transmitters is great they may have the urge to define the polarization at
>the receiver end. This would simplify having to explain to lay people way
>the signal they are observing is rotating CCW when it is defined as right
>hand polarization. There seems to be a lot of confusion and misunderstand of
>these concepts among some of our local hams.

Ben,
I agree that there is confusion.  A right-handed CP antenna is 
right-handed, regardless of whether it is used for Rx or Tx.  You can 
explain it to your local hams using the idea of a right-hand thread (or 
left-hand thread) on a bolt and matching nut.  The "handedness" is the 
same, whether you are screwing the bolt into the nut (receiving), or 
screwing the bolt out of the nut (transmitting).  The "clockwise-ness" of 
the rotation is reversed depending on whether the bolt (ie. signal) is 
coming or going, but this is not "handedness".  Yet another and better way 
to visualize this is with the so-called "right-hand rule" (also used for 
other things like vector math).  For right-hand circular polarization,  the 
fingers of your right hand curl in the direction of rotating polarity, your 
thumb points in the direction of propagation.   You can see that this is 
consistent with your argument above regarding CW or CCW rotation for 
Tx/Rx.  It is for this very reason that the concept of "handedness" is used 
for circular polarization, rather than using CW and CCW which are direction 
dependent.


-- 
  _______________________________________________________________________
  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
   Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
  _______________________________________________________________________

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