At 08:25 AM 4/16/2010, Rick - WA4NVM wrote:
Hi All,
A picture is worth a thousand words.........
http://sv1bsx.50webs.com/antenna-pol/polarization.html
Maybe this will help......
73, Rick WA4NVM
Subject: [amsat-bb] Re: Arecibo and circular polarization using cheap yagis
Or you can split the feedline equally if one antenna is spaced 1/4 wavelength ahead of the other. The relation of the fed elements determine whether you get RH or LH CP. The center conductor is connected to one side of the fed element (this is called the + side). If the antenna to the rear (or not with extra feedline) is vertical with "+" straight up and the other antenna has its "+" element pointing to the right, you get RHCP. Reverse it and you get LHCP.
73, Ed - KL7UW, WD2XSH/45
Hi Ed, KL7UW
Please find here a necessary amendment to your statement:
We assume that you are looking from the rear of the antenna in direction of propagation and one antenna is spaced 1/4 wavelenght ahead of the other.
If the dipole of the rear antenna is vertical with "+" straight up and if the dipole of the front antenna is horizontal and has its "+" element pointing to the left then you get RHCP. Reverse it and you get LHCP
In a separate email I have sent to you a drawing showing how two linearly polarized components shifted 90° one to the other adds togheter to generate a circularly polarized wave but I can send the same drawing to everybody need it.
For antennas in the "X" configuration (back antenna "+" up and to the left, front antenna "=" up and to the right for RHCP.
If the signe "=" is a typing mistake and you means " - " (minus) then your statement is correct.
73" de
i8CVS Domenico
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OK, that seems counterintuitive, but I guess I was not accounting for both driven elements to be fed in-phase. The electrical vector must rotate clockwise to produce RHCP, and so it does in Domenico's drawing. Dom's drawing actually shows the rear driven element horizontal and the forward driven element vertical, but its the relationship that produces the rotation so does not matter (i.e. they both could be angled +45 and -45 degrees in the "X" configuration). I guess my confusion was not accounting for both elements being driven in-phase.
My M2 436CP42 looks just like Dom's drawing but it has a 1/2 wavelength longer phasing line between the rear and front driven elements. They say this is the setup for RHCP? It would seem the M2 system would have the front antenna 180-degrees out of phase? So would that not produce LHCP? It is actually easier to visualize with both elements at the same point on the boom and one fed with a 1/4 wave longer feed line.
Nice thing about helical antennas is the corkscrew turns in the direction of the rotating wave.
73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010 DUBUS Magazine USA Rep dubususa@hotmail.com ======================================