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"<[email protected]> > To: "Rick - WA4NVM"<[email protected]>; "i8cvs"<[email protected]>; > "Douglas Quagliana"<[email protected]>; "amsat"<[email protected]> > 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 > > > > > > > > _______________________________________________ > Sent via [email protected]. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > > > > _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
