I went with the choice of a non metallic crossboom because originally I had planned to build CP antennas and thought it would be the best option. As it turned out, I decided against CP antennas at present because I didn't have the measuring equipment to properly determine the velocity factor of the coax used in the phasing harneses. I probably will eventually construct CP antennas, I even have a second set of aluminum rod elements for the 70 cm antenna,but I just decided to simplify things to start with. 73, Michael, W4HIJ ----- Original Message ----- From: "Edward Cole" kl7uw@acsalaska.net To: "Michael A. Tondee" mat_62@netcommander.com; amsat-bb@AMSAT.Org Sent: Saturday, April 05, 2008 12:50 AM Subject: Re: [amsat-bb] Re: cross boom?
If you are using linearly polarized yagis, just mount each vertical and separate horizontally about 5-6 feet using an aluminum crossboom. There is no need for non-metallic boom if the crossboom is perpendicular to the plane of polarization. Ideally, the separation would be so that the field of neither antenna were to touch, but practical separation of the field of the higher frequency antenna is sufficient. If you get cross-talk between VHF and UHF it may be and advantage to have one antenna place in the opposite polarization. Then mount each on a 45-degree slant -----/
I use two x-yagis mounte on metallic crossboom. The antennas are mounted in an X----X configuration and both are RHCP with no problem of cross-talk using up to 50w. Preamps are used with both antennas so either mode-UV or VU may be used. My crossboom is about 6-foot long and both antennas have about 18-foot booms.
73 Ed - KL7UW http://www.kl7uw.com/sat.htm for pictures
At 06:38 PM 4/4/2008, Michael A. Tondee wrote:
I used schedule 80 PVC with a large wooden dowel pushed inside for added rigidity. I sealed each end with epoxy. It's been going strong for a couple of years now. I saw your other post about antennas. At present I'm using a four element 2 meter beam and an 11 element 70cm beam in vertical polarization. Both are homebrewed using Ken Britain's "cheap yagi" design. 73, Michael, W4HIJ