[VHFcontesting] Elevation control ideas

steve d kc8qvo at yahoo.com
Wed Mar 14 02:00:43 EST 2007

Hi all, my friend Jim KC8JPZ and I are trying to figure out how to elevate some VHF/UHF antennas, but we hit a snag.
  The original idea to elevate the antennas was to use a lead screw type drive (like the TVRO dishes) with a turns counter on a 110vac drill motor (like a screwdriver antenna, only ac). We would have to figure some way of converting motor revolutions to degrees though. The problem here is that the ratio of motor revolutions to degrees is going to be a non-linear function. For example, say the angle between the screw drive and the array at 0deg is 45deg. As the screw pushes the array up that 45deg angle between the array and the screw decreases. Im not a mathmetitian, but something tells me that the ratio the screw travels to the angle the array is elevated to decreases as the distance the screw drives increases. 
  What do you guys think here? Is there a way to do this where the ratio between motor revolutions to elevation angle remains constant (besides using a gear or chain drive to rotate the array HI)? How have you made an elevation control? 
  It would be pretty easy to go out and buy a yaesu elevation rotor, but thats a bit of $$ and we like building our own stuff. All of our antennas are home-brew, now we just need a home-brew positioner HI. 
  Steve, KC8QVO

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