But what about antennas like the M2 ants where it's a balanced feed, and there is no + side of the element or coax?
The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com
On 4/16/2010 9:37 PM, i8cvs wrote:
----- Original Message ----- From: "Edward Cole"kl7uw@acsalaska.net To: "Rick - WA4NVM"wa4nvm@comcast.net; "i8cvs"domenico.i8cvs@tin.it; "Douglas Quagliana"dquagliana@aol.com; "amsat"amsat-bb@amsat.org Sent: Friday, April 16, 2010 8:20 PM Subject: Re: [amsat-bb] Re: Arecibo and circular polarization using cheap yagis
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.
73, Ed - KL7UW, WD2XSH/45
Hi Ed, KL7UW
What the M2 say is correct.
In a crossed yagi with vertical and horizontal elements spaced 1/4 wavelenght ( 90°) over the boom if you look from the rear of the antenna toward the direction of radiation the phase relations are as follows:
Assume that the power is splitted in two equal parts and the horizontal and vertical dipoles are feed in phase with equal lenghts of coax cable.
The inner conductor (+) of one coax cable is connected to the right side of the horizontal rear dipole. The inner conductor (+) of the other coax cable is connected to the upper side of the front vertical dipole.
With the above coax cable connections and +90° of phase shift over the boom the antenna radiates RHCP
If you now add a 1/2 electrical wavelenght (180°) to the coax cable supplying the front dipole then the polarization reverses in LHCP because 90° of mechanical shift over the boom minus 180° for the 1/2 wavelength of coax cable make a difference of - 90°
This is exactly what your M2 436CP42 does when switching between RHCP to LHCP
I agree with you that 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.
73" de
i8CVS Domenico
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