How add C + Ku Band LNBs on one Motorised Dish

[SatPak]

I want one satellite at a time. How can I get both LNBs (C&Ku) work on a motorised Dish. My solution of putting C Band to one side works only for the satellite I have aligned it for. The moment I rotate dish to other C-band satellites the signal drops drastically for one or two satellites then vanishes for the rest in the arc. In my country I dont have 2 in 1 feed horns.

 

[Magic Static]

Should be able to find a C/Ku LNBF like this http://www.titaniumsatellite.com/pr...-LNBF-Standard-LO/p/56000441/category=6743545

 

[Titanium]

The offset feedhorn will properly track the arc if it is mounted and optimized in alignment with the polar axis of the dish. The offset feedhorn should be mounted as close to the East or West side of centered feedhorn as possible. Many hobbyists cut the scalars to place the offset feedhorn close to the centered feedhorn.

A common mistake is the misunderstanding that the centered and offset feedhorns are both able to receive the same satellite at the same time. Typically, the dish must be moved East or West 4 or 5 degrees to "center" the offset feedhorn to receive the signals from the same target satellite.

For example: if the center KU LNBF is receiving programming from 97w and the C-band LNBF is mounted on the East side, the dish will need to be motored to the East to reflect the same 97w satellite signals into the offset LNBF. If the LNBF is not mounted at the correct height for the offset angle, the reflected signal will not enter the feedhorn throat.

 

[armadillo_115]

For example: if the center KU LNBF is receiving programming from 97w and the C-band LNBF is mounted on the East side, the dish will need to be motored to the East to reflect the same 97w satellite signals into the offset LNBF. If the LNBF is not mounted at the correct height for the offset angle, the reflected signal will not enter the feedhorn throat.

Now I'm confused.If the offset lnb is mounted on the East side say 6 degrees off center ....wouldn't you have to motor it WEST 6 degrees to hit the same Satellite?

Maybe I'm thinking bassackwards.

 

[Titanium]

The reflection into the offset feedhorn is a mirror image. If feedhorn #1 is centered and looking at 97w, 6 degree offset feedhorn #2 on the East side would be looking at satellite 103w (97 + 6 = 103). A feedhorn mounted on the East side of the centered feedhorn will be looking at a satellite on the West side of the center satellite. A feedhorn mounted on the West side of the centered feedhorn will be looking at a satellite on the East side of the center satellite.

To have feedhorn #2 looking at 97w, drive the dish East 6 degrees (103 - 6 = 97).

 

[armadillo_115]

Ok...trying to get this fixed in my head.
So you motor East to receive a satellite to the West. (on the offset lnb) Dish angle gets more oblique with each successive satellite.
I'm guessing the off-set lnb receives progressively worse the farther you motor in either direction away from 'center' ? If so,can the whole arc still be received?

Forgive my ignorance,and thanks for explaining Titanium!

I'd like to understand the concept before I actually try mounting an offset KU lnb.
<Gone back to the dunce corner>

 

[Titanium]

Ignorance is the absence of the desire to learn. You are far from ignorant or a dunce. Get out of that corner and out to the satellite dish playground!

The main issue that comes into play for multiple satellite reception is that the visual spacing between satellites is greater near the top of the arc and tighter nearing the horizon. This separation between satellites is also greater closest to the equator and tighter for northern install locations.

This is an easy fix for offset feedhorns as the motor count offset can be optimized for each satellite positon and is not fixed. No different than when programming a single feed motorized dish.

 

[FaT Air]

You can confirm this at dishpointer.com , The List satellite calculator, and others.
Check the azimuth difference between two satellites near your true south, And two, equally spaced, satellites near the horizon.

 

[armadillo_115]

I know where my thunking was wrong.I need a sharper pencil or better protractor.lol

I didn't mean to highjack SatPak's thread.

 

[SatPak]

I am so grateful for the lively discussion.In Islamabad we need to put the off-set LNB to the right (around 45 degrees ) of the prime /centered LNB, i.e not exactly adjacent. When the polar mount rotates the dish LNB relevant position changes accordingly.Stil I think I'll have to work more on it as the situation has worsened after I realigned my dish to get much stronger Ku band signals now.My side-LNB (as they call it in Pakistan) is C-Band and I am using a locally made very good dish by Shabbir. Enthusiasts in Pakistan have really done some marvelous settings.They get 40 satellites on three dishes.You can google down to the images to see.

 

[Titanium]

If the offset feedhorn is located at 45 degrees from centered, it will not track the arc. The offset feedhorn needs to be placed as close as possible to the center feedhorn to allow arc tracking

 

[FaT Air]

When the dish is aimed directly south, the feed on the side has to be directly left or right of the centered feed. Else it will look above or below the arc.