1.2M Primestar Dish on Polar Mount

[ziggy1222]

Here are some pics of a 1.2M Primestar dish on a polar mount. I spent countless hours trying to get it to track the arc and was unable to do so. I then added a second actuator which only has to move 1-2 inches to overcome the tracking error. I used 1/1/2" by 1/4" steel bars spaced 7" apart and drilled holes 7" apart in each bar to match the mounting holes of the 1.2M dish. Thats an ExpressVu Dish Network linear dual LNBF mounted in the feedhorn cradle.

 

[Anole]

The 1.2m Primestar is an offset feed dish, and looks "up" about 22° from a line perpendicular to the dish face.
SO, you need to make the dish look "down" about 22°, and then the declination and other motion of the mount you've used (good choice), will track just fine on the single motor. - :up
In other words, use some spacers or brackets to tilt the dish down (forward/lnb toward the ground) on it's mount, and you'll be golden.

Member TurboSat did this same sort of thing a year or two ago.
Look up his thread for more discussion on the matter.

 

[ziggy1222]

I tried that...if you look closely at my steel bars you will see an extra set of holes in them. I had the side of the dish near the actuators proped up and I still couldn't get it to track. But if you prop it up isn't the same thing as changing the elevation? And also would you only raise it 11 degrees because the signal bounces in from the atmosphere at an 11 degree angle and reflects back another 11 degrees to the LNBF?

 

[phlatwound]

You would need to set the elevation bar on your polar mount to the correct amount for your latitude, then tilt your dish down the amount of your declination + however many degrees that your dish is offset.

What are you driving the 2 actuators with?

I can see how your setup would work but if you set that rig up properly you won't need an actuator on the elevation.

 

[Anole]

I tried that...if you look closely at my steel bars you will see an extra set of holes in them. I had the side of the dish near the actuators proped up and I still couldn't get it to track. But if you prop it up isn't the same thing as changing the elevation?

Sorry, I just don't see in the pictures what you are saying.
Maybe after I have a nap, eh? -

And also would you only raise it 11 degrees because the signal bounces in from the atmosphere at an 11 degree angle and reflects back another 11 degrees to the LNBF?

Well, not exactly.
I see where you have the two vertical rusty bars bolted to the back of the dish.
I see the ring part of your mount, which originally bolted to the back side of a BUD, and has the far end of the motor attached to it.
The bars seem to be flush with the ring.
You need to tilt the bars (and dish) forward so the top of 'em is spaced well away from the ring.
Then, you need to measure the angle between the bars and the face of your ring, and set it to arouund 23°.
We can look up the correct number, but this'll get you close. (somewhere between 22° and 26°, I think)

 

[ziggy1222]

I'm driving one of the actuators with a Uniden UST7700at and the other one with a General Instrument 350iPS...just some actuator only power supplies.

 

[turbosat]

Hard way to do it, but crafty !! I always wanted to try that, but it'd be slow as hell changing satellites and getting all those angles right with two motors. The other guys are right, if you build in enough off set to the dish you wouldn't need another actuator. I used a polar mount just like that, and found I had to remove the U-shaped clamp off the bottom of the ring, to get more space for 'declining' the dish. And still didn't get enough room so I had to build in more space. It was a learning project, for sure. You can use the aiming figures for a fixed offset dish on any given satellite, and find that angle of elevation with an angle meter placed on the front of the dish, while your polar mount is aimed at that satellite. You'll be able to see how much space is needed to add. I did learn one thing, after a week of trying, there is NO way the polar mount will track the arc unless it is set properly to your site's elevation. I thought adding in a little extra elevation would allow my offset dish to work without any other adjustments. It did, but only for a handful of satellites right in the middle of the arc, lol.

 

[ziggy1222]

On my secondary actuator the pulse is not working so what happens is that it moves ever so slightly and then stops. This actually helps as I have a Channel Master meter in line and use these mini movments to peak the signal.

 

[tvropro]

Having a separate elevation adjustment has some benefits I would think. Since you can fine tweak all angles. Next we need to find a way to motorize the focal distance then when it comes to alignment time we could do it all with with remotes. :up Sure would beat the heck out of going out there in a snowstorm to fix alignment.