[amsat-bb] Re: Arecibo and circular polarization using cheap yagis
nss at mwt.net
Fri Apr 16 19:51:05 PDT 2010
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
On 4/16/2010 9:37 PM, i8cvs wrote:
> ----- Original Message -----
> From: "Edward Cole"<kl7uw at acsalaska.net>
> To: "Rick - WA4NVM"<wa4nvm at comcast.net>; "i8cvs"<domenico.i8cvs at tin.it>;
> "Douglas Quagliana"<dquagliana at aol.com>; "amsat"<amsat-bb at amsat.org>
> Sent: Friday, April 16, 2010 8:20 PM
> Subject: Re: [amsat-bb] Re: Arecibo and circular polarization using cheap
> 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
> 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
> 73" de
> i8CVS Domenico
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