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Antenna Separation

Hi folks.  What kind of separation is typically necessary for a pair of crossed yagis and a dish on the same az/el rotor?

I plan to build a cheapo hand-crank elevation rotor (hinges, wood, all-thread rod, 3/8 socket speed wrench, etc.), and am leaning towards 
buying the cheapo Rat Shack TV rotor for azimuth.  On top of that will be a wooden horizontal boom holding a CP Yagi for 2m, a CP Yagi for 
70cm, and a 60cm dish for 13cm.

Yes, this is way more than the Rat Shack rotor is intended to hold, and it's a pretty sloppy rotor (especially with all the junk we plan to put on it), 
but it's cheap (about $70) and this is just a Field Day install.  If we get high winds, we'll run for cover. =:o  If anyone has any good ideas for a 
cheaper way to accomplish azimuth rotation at the top of 10-15 feet of pole, please share it with me.  It doesn't need to be fancy, but it does 
need to work, and stay more-or-less where pointed for a while.  Extra credit is given for designs that require little or no welding and use 
materials I can find at a good hardware store.

Anyway, I've seen pictures of a cross-boom with 2m at one end, 70cm at the other, and a dish in/near the center.  How far apart do I need to 
make them to avoid interaction?  I don't think we'll be shooting for AO-10, so our output power shouldn't be too high for the other birds, I don't 
think (AO-40, FO-20, FO-29, maybe the RS birds).  I'm thinking about putting the Yagis at least 2m apart (1 wavelength), with the dish in 

David, ky0dr

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