[amsat-bb] Re: Circular Polarization with Two Yagis (Spacing)

i8cvs domenico.i8cvs at tin.it
Thu May 30 21:23:04 PDT 2013

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 at gmail.com>
To: <amsat-bb at 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.jpg
> It would be great to refine his good work with the spacing for the 2
> (Then I may compare with putting all the elements on one boom)
>  I like the collaborative nature of the discussion here.
> --
> Thanks,
> Mike
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