Hi Mike,
I suggest you to mount the elements over a single aluminum boom The elements must be crossed over the boom and must be mounted like the signe X because it is easer and less complicated than that you plan to do.
To get circular polarization the elements must be spaced over the boom by a 1/4 wavelenght in air i.e. 52 centimeters or 20.36 inches for 145 MHz
Using the above configuration if you feed the X elements with the same lenght of transmission line than they are supplied in phase but since the elements are shifted 1/4 wavelenght over the boom than you produce circular polarization.
The sense of polarization can be RHCP or LHCP depending on how you have connected the inner conductor and the bride of the coax cables to the feed points of the dipoles.
BTW if you want to reverse the sense of polarization you must supply the front dipole closest to the satellite adding a 1/2 of electrical wavelength of coax cable swiching it with a coax relay.
For 145 MHz the 1/2 electrical wavelenght of coax cable can be made using 69 centimeters of RG-213
If you need more detailed informations I can send to you a schematic diagram of the system with descriptions in italian.
have fun
73" de
i8CVS Domenico
----- Original Message ----- From: "Mike Sprenger" mikesprenger@gmail.com To: amsat-bb@amsat.org Sent: Friday, May 31, 2013 2:51 AM Subject: [amsat-bb] Circular Polarization with Two Yagis (Spacing)
Hi,
I'm sure this has been covered, I just can't find some detail.
I'd like to consider taking a pair of say 3, 5, or even 11 element 2M yagi's (off the shelf) and put them on a boom on either side of a rotor, with nonconductive cross support boom, rotating the boom's to offset the elements 90 degrees.
Question I have, what would the spacing be between the two yagi's ?
Jerry has done this with success on 2 meters:
http://www.n0jy.org/images/IMG_20120623_215906.jpgIt would be great to refine his good work with the spacing for the 2
booms.
(Then I may compare with putting all the elements on one boom)
I like the collaborative nature of the discussion here.
-- Thanks, Mike _______________________________________________ Sent via AMSAT-BB@amsat.org. 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