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DISH SETUP: Single sat, Multi-Sat & Motorised
Re-installing dish and tracking the arc
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<blockquote data-quote="deeptho" data-source="post: 1124081" data-attributes="member: 215446"><p>There is an interesting test which I performed yesterday to check disalignment:</p><p>tune to a satellite in an inclinded orbit and observe how the snr goes up and down.</p><p></p><p>If properly aligned, the signal should peak at the time kingofsat.net reports that</p><p>the satellite has zero declination. If your dish is not properly aligned, wait until</p><p>the signal peaks, and then the sateliite's declination will tell you</p><p>if you are pointing above or below the arc and by how much. The accuracy will</p><p> be of the order of 0.4-0.7 degrees. I still need to refine this to draw conclusions on</p><p>my own dish (probably it pointed 0.4 degrees off at this position)</p><p></p><p>Of course, to know what to adjust on the dish, you would need a similar measurement on an eastern</p><p>sat....</p><p></p><p>I have found it helps a lot if you can set the rotor axis exactly right, because afterwards it becomes a lot easier to</p><p>adjust declination and azimuth</p><p></p><p>So: make your own inclinometer out of a large piece of cardboard, some thin thread and some</p><p>weight (e.g., a keychain). I have made one out of a 40cm board which shows 1, 2 ... 10 degrees from vertical. It is precise</p><p>up to less than 0.2 degree or so and much better than these electronic devixes which can be off by a degree even when</p><p>claiming 0.1 degree accuracy</p><p></p><p>The first step in the adjustment (starting from what you have now) is to rotate the dish to the exact south using the receiver</p><p>("goto 0", "reset" or add a fake satellite at zero degrees and move to that sat). Do NOT use a "close to south at". You really need</p><p>usals=0 exactly.</p><p></p><p>Then (and only then) check if the distance from the left edge of the dish to the rotor axis is exactly the same as from the right</p><p>edge to the rotor axis. Use the closest point on the rotor axis for these measurements. If the distances</p><p>are incorrect, rotate the dish around the rotor axis to make them correct. Afterwards tune to a satellite near</p><p>to south and now rotate the whole assembly around the pole to peak the signal. This is needed to compensate for the</p><p>first adjustment, which will have decreased the signal level.</p><p></p><p>Then, measure the angle on the rotor's axis with the cardboard inclinometer.</p><p>If needed adjust the elevation of the rotor to the correct value which can be computed using online calculators (modified usals angle).</p><p>This is the angle between the rotor and the vertical direction when measured between the rotor axis and the pole (so approx. in the north-south dirction. In my case this should be 3.3 degrees but it is 3 degrees. This level of accuracy is enough according to my calculations</p><p>(and I can track from 53 east until 45 west) but I would prefer to have it slightly better.</p><p></p><p>Also make sure the angle of the rotor axis to vertical is exactly 0 when measured in the east/west direction.</p><p>This will be the case when the pole is plumb and the rotor pole attachment has not been deformed by wrong tightening</p><p></p><p>When all of this is done, the rest is very easy: point to any sat using the receiver (by setting the correct usals</p><p>value for the satellite). Use a sat close to the south. Then adjust the dish declinationto peak the signal.</p><p>After this the arc should be tracked perfectly, but some minute adjustments of elevation can help. For this,</p><p>tune to a weak sat to the east or west. It can get you another 0.5 - 1dB.</p><p></p><p>This approach is less frustrating than the trial and error approach. The procedure outlined by captain Jack</p><p>will not be needed, but it is a valid procedure.</p><p> </p><p>And of course: SNRs change from transponder to transponder, so one value per sat will not tell you much...</p><p></p><p>The trick with the inclined satellite can help you to determine the maximum possible snr or signal levels.</p><p>Just observe the signal over a period of an hour or two around maximum, using the receiver to move slightly east or west</p><p>to peak the signal from time to time. Once you know the maximum value, then compare it to the value when the satellite</p><p>reaches zero declination. If the difference is very small then your dish is properly tuned....</p><p>THis assumes that the weather has not changed in the mean time...</p><p></p><p></p><p>PS. Be careful. satellite receivers sometimes decide to move the rotor and instead of the rotor pointing south it then</p><p>may point somewhere else.</p></blockquote><p></p>
[QUOTE="deeptho, post: 1124081, member: 215446"] There is an interesting test which I performed yesterday to check disalignment: tune to a satellite in an inclinded orbit and observe how the snr goes up and down. If properly aligned, the signal should peak at the time kingofsat.net reports that the satellite has zero declination. If your dish is not properly aligned, wait until the signal peaks, and then the sateliite's declination will tell you if you are pointing above or below the arc and by how much. The accuracy will be of the order of 0.4-0.7 degrees. I still need to refine this to draw conclusions on my own dish (probably it pointed 0.4 degrees off at this position) Of course, to know what to adjust on the dish, you would need a similar measurement on an eastern sat.... I have found it helps a lot if you can set the rotor axis exactly right, because afterwards it becomes a lot easier to adjust declination and azimuth So: make your own inclinometer out of a large piece of cardboard, some thin thread and some weight (e.g., a keychain). I have made one out of a 40cm board which shows 1, 2 ... 10 degrees from vertical. It is precise up to less than 0.2 degree or so and much better than these electronic devixes which can be off by a degree even when claiming 0.1 degree accuracy The first step in the adjustment (starting from what you have now) is to rotate the dish to the exact south using the receiver ("goto 0", "reset" or add a fake satellite at zero degrees and move to that sat). Do NOT use a "close to south at". You really need usals=0 exactly. Then (and only then) check if the distance from the left edge of the dish to the rotor axis is exactly the same as from the right edge to the rotor axis. Use the closest point on the rotor axis for these measurements. If the distances are incorrect, rotate the dish around the rotor axis to make them correct. Afterwards tune to a satellite near to south and now rotate the whole assembly around the pole to peak the signal. This is needed to compensate for the first adjustment, which will have decreased the signal level. Then, measure the angle on the rotor's axis with the cardboard inclinometer. If needed adjust the elevation of the rotor to the correct value which can be computed using online calculators (modified usals angle). This is the angle between the rotor and the vertical direction when measured between the rotor axis and the pole (so approx. in the north-south dirction. In my case this should be 3.3 degrees but it is 3 degrees. This level of accuracy is enough according to my calculations (and I can track from 53 east until 45 west) but I would prefer to have it slightly better. Also make sure the angle of the rotor axis to vertical is exactly 0 when measured in the east/west direction. This will be the case when the pole is plumb and the rotor pole attachment has not been deformed by wrong tightening When all of this is done, the rest is very easy: point to any sat using the receiver (by setting the correct usals value for the satellite). Use a sat close to the south. Then adjust the dish declinationto peak the signal. After this the arc should be tracked perfectly, but some minute adjustments of elevation can help. For this, tune to a weak sat to the east or west. It can get you another 0.5 - 1dB. This approach is less frustrating than the trial and error approach. The procedure outlined by captain Jack will not be needed, but it is a valid procedure. And of course: SNRs change from transponder to transponder, so one value per sat will not tell you much... The trick with the inclined satellite can help you to determine the maximum possible snr or signal levels. Just observe the signal over a period of an hour or two around maximum, using the receiver to move slightly east or west to peak the signal from time to time. Once you know the maximum value, then compare it to the value when the satellite reaches zero declination. If the difference is very small then your dish is properly tuned.... THis assumes that the weather has not changed in the mean time... PS. Be careful. satellite receivers sometimes decide to move the rotor and instead of the rotor pointing south it then may point somewhere else. [/QUOTE]
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DISH SETUP: Single sat, Multi-Sat & Motorised
Re-installing dish and tracking the arc
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