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Installation questions -focal length, skew, horn inclination

Discussion of large prime focus satellite dishes used for C-Band signal reception.
beekeeper
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Installation questions -focal length, skew, horn inclination

Post by beekeeper » Sun Nov 02, 2014 11:08 pm

blah blah
Last edited by beekeeper on Wed Dec 17, 2014 8:12 am, edited 1 time in total.

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fatso
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Re: Installation questions -focal length, skew, horn inclina

Post by fatso » Mon Nov 03, 2014 9:12 pm

beekeeper wrote:For the 10 ft dish (from tek2000), is the focal length 48.5" from the edge/rim of the LNBF (after removing the plastic cap) to the center plate of the dish?
Focal length is usually measured from the side of the scalar ring facing the panels to the center of the dish plate. You might also add an extra 1/2 inch because the face plate is not the vertex where the panels would theoretically meet if they extended further.

Don't worry too much about getting this measurement exact because you will be able to move the LNBF in/out of the scalar ring to peak the signal. Just make sure your get a ball park figure of 48.5" when you install the LNB rods and scalar ring. If you measure something like 40 inches or 55 inches, then you are off and need to start worrying... :roll:
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Re: Installation questions -focal length, skew, horn inclina

Post by fatso » Mon Nov 03, 2014 9:15 pm

beekeeper wrote:Do I need to set C-band LNBF skew? If so by how much? Clockwise or counterclockwise? 0 deg skew is at true South (190 deg magnetic) right?
Don't sweat it. Set the skew approximately to zero when pointing true north/south. Once you lock your first signal, adjust the skew to peak the signal.
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Re: Installation questions -focal length, skew, horn inclina

Post by fatso » Mon Nov 03, 2014 9:17 pm

beekeeper wrote:Or I just set the skew to zero at the true South, and the skew will be adjusted (as viewed from the satellite) when the dish moves along the arc?
Exactly right. As the dish moves along the arc, the skew adjusts itself to teh correct value. You just need to lock on one bird and peak it. After that, it will be aligned for the whole arc.
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Re: Installation questions -focal length, skew, horn inclina

Post by fatso » Mon Nov 03, 2014 9:23 pm

beekeeper wrote:In my case, should the scalar ring inclination be 39.1 deg or 45.8 deg?
45.8 deg.

Declination usually refers to the total angle: elevation + declination offset
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beekeeper
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Re: Installation questions -focal length, skew, horn inclina

Post by beekeeper » Mon Nov 03, 2014 10:01 pm

blah blah
Last edited by beekeeper on Wed Dec 17, 2014 8:13 am, edited 1 time in total.

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Re: Installation questions -focal length, skew, horn inclina

Post by tvroadmin » Tue Nov 04, 2014 2:13 am

LNB support rods are manufactured to the correct length for each particular dish...so I wouldn't worry about that. Just bolt them on to the dish and away you go!
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beekeeper
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Re: Installation questions -focal length, skew, horn inclina

Post by beekeeper » Mon Dec 01, 2014 7:22 pm

blah blah
Last edited by beekeeper on Wed Dec 17, 2014 8:13 am, edited 1 time in total.

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mountainman
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Re: Installation questions -focal length, skew, horn inclina

Post by mountainman » Mon Dec 01, 2014 11:01 pm

You are not tracking the arc properly. Remove all switches and use a simple C-band LNBF with single output to receiver. Once you track the arc from 55W to 137W, then you can start playing around with switches and more complicated LNBs.

As for switches, not sure which ones you are using. What are you trying to do? Route the same signal to 2 or more different receivers or have one receiver switch between 2 or more signals? If you are doing the latter, then there won't be any power less (or very little). If you are doing the former, then you are splitting the signal and there will be a -3dB loss for each split but this loss occurs AFTER the RF amplification stage so it will only affect the weakest signals which are near the noise threshold.
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Re: Installation questions -focal length, skew, horn inclina

Post by mountainman » Mon Dec 01, 2014 11:06 pm

beekeeper wrote: And if I wanted only one receiver connected to my ortho setup, I could use power inserters and one 22 kHz switch (and configure horizontal transponders to output 22 kHz tone and 0kHz for vertical). That should work, no?
Yes, this will work. You could also use a 2x1 DiseqC switch (e.g. Port 1 and Port 2).
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