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AzBox Americas support forum  |  Feed hunting  |  System installation and maintenance  |  Lining up the arc on a polar mount C-band dish
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Author Topic: Lining up the arc on a polar mount C-band dish  (Read 1917 times)
FeedHunter
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« on: February 15, 2015, 06:41 pm »

Aligning your polar mount C-band satellite dish so that it tracks the Clarke belt can seem to be a challenging task for most people.  However, it can easily be done by following the instructions below.

Before you begin the alignment, a working satellite meter or receiver programmed with currently active transponders is required.  At the very least, you should ensure that transponders from an active and receivable satellite with an orbital position close to your location's longitude are programmed in.  This is referred to as the "true south" satellite and will be used to locate the first signal during the alignment process. 

Several satellite channel listings exist in order to obtain currently active transponders such as http://cband.fta.channels.drsat.ca or http://www.lyngsat.com/america.html

You will also need to obtain an inclinometer in order to measure and adjust the elevation and declination of your dish which can be purchased from any hardware store.

Set polar mount declination and elevation.
Move the dish to the highest point in its travel arc, i.e. centering the dish at its zenith. Do this by using the actuator; it can be done by visually looking at the dish. It is now time to set your declination/elevation angles. I use a common carpenter's inclinometer, with magnetic base, to set angles. I like it better than the much more expensive digital inclinometer - especially since I seem to drop it all the time, or forget and leave it on the mount and it gets knocked off to the ground when I am checking the sides or the arc, or forget and leave it on the mount and it gets rained on!!


Use the above chart to get the elevation and declination values to use based on your location and use your inclinometer on your dish's polar mount to adjust both angles as per the above diagram.

First set the elevation angle, it is measured on the polar axis (sometimes the elevation angle is called the polar axis angle). By elevation, it means the angle in degrees which the dish must be tilted up from the horizon prior to addition of the declination angle.  This angle can be measured by placing your inclinometer at position A in the above diagram.

The declination is an adjustment that tilts the dish 'forwards' at an angle depending on what latitude you live. This adjustment is usually measured on one of the mounts connected directly to the dish, i.e. in the plane of the dish but on its back ring as per position B in the above diagram.

You should NOT have to change the elevation angle beyond this point. It is the easiest angle to set accurately (especially with a digital inclinometer) and remains fixed. The declination offset angle is the next easiest angle to set accurately and the hardest adjustment is the true north/south alignment of the dish (azimuth angle = 0 degrees).

With that being said, our strategy for alignment and tracking the satellite arc will be as follows:

1. Adjust the Azimuth (true north/south) alignment first by rotating the dish about the pole until the first satellite signal is received.
2. Adjust the LNBF skew and focus to peak the first signal received.
3. Adjust the Declination Offset angle to peak signals from satellites low in the arc.
4. Finally, fine-tune the Elevation, Declination Offset, Azimuth and LNBF skew for maximum efficiency.

Make sure you follow the strategy above or you will mess up the alignment. The biggest mistake people make is thinking azimuth doesn’t play a large role or that the dish is pointed true south and they begin fiddling with elevation and declination adjustments instead. Remember, the average magnetic compass isn’t that accurate and its unlikely that you have a more sophisticated method of pointing the dish true south. So you have to work with the assumption that the azimuth is off to begin with.

It is worth saying one more time: DO NOT adjust the elevation angle and declination offset angle until you are absolutely positive that the azimuth angle is correct. You will know that the azimuth angle is correct when you can track the arc symmetrically on both sides of the arc. If one side tracks better than the other, then the azimuth angle is incorrect.

The first satellite you need to track is the one closest to the zenith or top of the arc. For example, if you were in Buffalo, NY with longitude 78.8 west, you would try to track Simon Bolivar at 78W or AMC 9 at 83W. You should only worry about C band signals for now because due to their longer wavelength, they are easier to find. After finding the arc, you can track Ku band signals to fine-tune your dish alignment.

Start moving the dish with the actuator around the top of the arc until you receive your first signal. If you can’t lock any signals, barely loosen the cap bolts and rotate the dish slightly about the pole and try again. Be sure to mark the starting point on your pole for your reference. If you still don’t register any signals, try rotating the dish some more. If still nothing, rotate the dish in the opposite direction and repeat the procedure.

Once you register the first signal, immediately adjust the LNBF skew and focus settings in order to peak the signal. After this point, you can assume your LNBF has been adjusted correctly and will only require fine-tuning (if any) later on.

Now that you have the top of the satellite arc in view, drive the dish east and west and program each satellite you find into your controller or receiver. Fine tune the mount rotation of the dish until you can track as many satellites as possible on both sides of the arc. As a general rule of thumb if you can track more satellites further west than east, you should slightly rotate the mount east and vice-versa.

To fine tune the Azimuth (north/south alignment), do the following:

1. Point your dish at the most extreme western satellite you can track and gently raise/lower the bottom lip of the dish. If raising the lip improves the signal, slightly rotate the mount to the west. If lowering the lip improves the signals, slightly rotate the mount to the east.

2. Point your dish at the most extreme eastern satellite you can track and gently raise/lower the bottom lip of the dish. If raising the lip improves the signal, slightly rotate the mount to the east. If lowering the lip improves the signals, slightly rotate the mount to the west.

When you are satisfied with the true north/south alignment of the dish and you can track the arc symmetrically on both sides, you should lock the cap bolts in place. You should not have to rotate the dish about the pole again except for fine-tuning if necessary.

To properly track the satellites located at the bottom of the arc, you will have to adjust and fine tune the declination offset angle which has the greatest effect on signal reception for these satellites.

"Philosophy of tuning satellite arc"

To fine tune the Declination Offset angle, do the following:

1. Point your dish at the most extreme eastern/western satellite you can track and gently raise/lower the bottom lip of the dish. If raising the lip improves the signal, subtract declination offset. If lowering the lip improves the signal, add declination offset.

2. Track the next most extreme eastern/western satellite and repeat the above procedure.

When you are satisfied with the signal reception of the horizon satellites, lock the declination screw in place.

After making true north/south and declination offset adjustments, you need to drive the dish back to the top of the arc and observe signal reception again. If the small adjustments you made reduced the signal strength at the top of the arc, fine-tune the elevation setting until you achieve maximum signal strength again.

You should ONLY make elevation adjustments when at the top of the arc.  Do not be tempted to make declination or azimuth adjustments at the top of the arc because it will simply throw your alignment off

"Tweaking dish"

Now that you can track the arc successfully, you will probably want to fine-tune each angle in order to maximize the efficiency of your C-band dish.

The best way to do this is to make a list of all the satellites along the entire arc and pick one transponder frequency from each satellite. Drive the dish to each satellite and record the best signal quality for this frequency.

Now fine-tune each angle one at a time and drive the dish over the entire arc recording the new signal qualities. If you notice some improvement, you can keep the new angle, otherwise revert to the previous angle.

Keep the following in mind when fine-tuning the alignment:

1. Fine-tuning the Elevation angle has the most effect at the TOP of the arc.
2. Fine-tuning the Declination Offset angle has the most effect at the bottom of the satellite arc.
3. Fine-tuning the LNBF skew and focus adjustment has equal effect throughout the satellite arc.
4. Fine-tuning the Azimuth (true north/south) ensures symmetrical tracking east/west of the top of the arc.


The procedure for tracking Ku band satellite signals is the same as C band satellite signals. Since the wavelength of Ku band signals is much smaller, even the slightest adjustments will have a large effect on Ku band reception – that’s why C band signals are tracked first because they are much easier to find in the first place! In general, if you can track C band signals along the arc, you will also receive the majority of Ku band signals, but you may have to fine-tune the alignment a bit.

Reference: Ricardo's Geo-Orbit Quick-Look
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