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Another useful thing to know: in the northern hemisphere, satellite dishes point south. In the southern hemisphere, they point north. This is because geostatio

by schoen 4y ago

Another useful thing to know: in the northern hemisphere, satellite dishes point south. In the southern hemisphere, they point north. This is because geostationary orbits (where satellites that communicate with fixed satellite dishes are located) are all above the equator. https://en.wikipedia.org/wiki/Geostationary_orbit https://en.wikipedia.org/wiki/Geostationary_orbit So, these dishes are aimed at a point above the equator (possibly with some eastward or westward component, but mainly southward).

hunter2_ 4y ago
And the angle they point up is (very roughly) the inverse of the latitude. A dish near the equator (0 degrees latitude) points 90 degrees up, a dish near the pole (~80 degrees latitude) points 0 degrees up (tangent line), a dish halfway between there and the equator points about 45 degrees up, and so forth. Page 122 has a handy table with the more precise+accurate lookups (shifted away from the pole since the satellite's altitude is quite a bit shy of infinity, at 35,800km): https://www.ngs.noaa.gov/CORS/Articles/SolerEisemannJSE.pdf https://www.ngs.noaa.gov/CORS/Articles/SolerEisemannJSE.pdf
- perilunar 4y ago
  That's true for dishes where the feed horn/antenna is inline with the dish axis. A lot of smaller satellite dishes nowadays use off-axis feeds. But you can do a bit of mental geometry to adjust.
defrost 4y ago
Assuming they're communicating with a geostationary sat of course - and the vast majority of sats these days just aren't (Starlink constellation being an obvious example of thousands). Even the quote from the wikipedia article [1] is dubious: > Weather satellites are also placed in this orbit for real-time monitoring and data collection as many weather and climate satellites are on near earth polar precession orbits to rapidly scan (obit time between one and two hours) a full circle about the planet for a full picture. [1] https://en.wikipedia.org/wiki/Geostationary_orbit https://en.wikipedia.org/wiki/Geostationary_orbit
- schoen 4y ago
  That's a good point. Still, the use of a fixed parabolic reflector dish involves aiming it at something, which would ordinarily be a point in the sky where there is a particular satellite, hence a geostationary orbit. For other applications where the satellite move around, I wouldn't expect the antenna to be a parabolic dish. It looks like Starlink's isn't, although their original one is more curved than I'd have expected. Maybe I'll modify this advice in the future and say "the curved satellite dishes that aim at a point in the sky are pointing south".

by schoen 4y ago

hunter2_ 4y ago

And the angle they point up is (very roughly) the inverse of the latitude. A dish near the equator (0 degrees latitude) points 90 degrees up, a dish near the pole (~80 degrees latitude) points 0 degrees up (tangent line), a dish halfway between there and the equator points about 45 degrees up, and so forth. Page 122 has a handy table with the more precise+accurate lookups (shifted away from the pole since the satellite's altitude is quite a bit shy of infinity, at 35,800km): https://www.ngs.noaa.gov/CORS/Articles/SolerEisemannJSE.pdf https://www.ngs.noaa.gov/CORS/Articles/SolerEisemannJSE.pdf

perilunar 4y ago
That's true for dishes where the feed horn/antenna is inline with the dish axis. A lot of smaller satellite dishes nowadays use off-axis feeds. But you can do a bit of mental geometry to adjust.

defrost 4y ago

Assuming they're communicating with a geostationary sat of course - and the vast majority of sats these days just aren't (Starlink constellation being an obvious example of thousands). Even the quote from the wikipedia article [1] is dubious: > Weather satellites are also placed in this orbit for real-time monitoring and data collection as many weather and climate satellites are on near earth polar precession orbits to rapidly scan (obit time between one and two hours) a full circle about the planet for a full picture. [1] https://en.wikipedia.org/wiki/Geostationary_orbit https://en.wikipedia.org/wiki/Geostationary_orbit

schoen 4y ago
That's a good point. Still, the use of a fixed parabolic reflector dish involves aiming it at something, which would ordinarily be a point in the sky where there is a particular satellite, hence a geostationary orbit. For other applications where the satellite move around, I wouldn't expect the antenna to be a parabolic dish. It looks like Starlink's isn't, although their original one is more curved than I'd have expected. Maybe I'll modify this advice in the future and say "the curved satellite dishes that aim at a point in the sky are pointing south".