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Finding a new satellite

(Read 3199 times)
Guy Thorton
Ex Member


Apr 20th, 2014 at 2:33pm  
Hi there!
I've recently gotten a new job as a satellite operator and whereas I've gotten lots of training on how to find satellites, I've only been given the basics. I know that I'll be thrown into some situations down the road where I'll need to find a new satellite that I haven't been trained to find and I was hoping that someone here could help me out.

First off, I found the sat finder calculator on here and want to further test it out in some areas I know, but I can't at the moment. The one spot I tested it out on was spot on! It said elevation 31.66 and I am at 31.6. Pretty amazing, so I'm anxious to try out other spots.

Anyway, my question is: How can I find a satellite using the longitudes? AMC1 is at 103 degrees, Galaxy 17 is at 91 degrees, echostar is at 119, etc. What do these numbers actually mean? Are they the position in the sky? Degrees from what? If I'm pointing to Galaxy 17 in New York and then need to point at it when I'm Vancouver, how can I use the longitude to help orient my satellite?

I have plenty of other questions, but those can come later. Thank you all in advance for your help/tips.
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Oasis Networks
Ex Member


Reply #1 - Apr 20th, 2014 at 5:14pm  
Hello Guy,

Regarding your first question - yes, those numbers are the orbital slot, meaning the longitude position of the satellite. Those are given relative to Greenwich which is 0. Geostationary satellites are fixed in their orbital slot, around 36,000Km above the equatorial, in the area called the Clarke belt.

Just try to google for geostationary satellite, Clarke belt, orbital position etc and I am sure you will get lot of useful information.

There are many online calculators to calculate the azimuth, elevation and other parameters for pointing a dish.

Regards,
Nimrod
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Alphaco
Ex Member


Reply #2 - Jul 13th, 2014 at 10:02am  
I had a client - although a former terrestrial VHF comm tech for oil rigs, he had tried to point his dish to astra 19.2E, and he pointed it to an azimuth of 19.2 degrees, which is north-east! (zero being north, 90 east, 180 south, and 270 west)

This just made it obvious to me that the following thing has to be explained to beginners about the sat positions in degrees: these figures describe the position of the subsatellite point on the equator, (the point right down vertically under the satellite).
Seen from the UK, a satellite on 0 would be due south, while a satellite on 19.2E would not be just 19.2 left (east) from south (180-19.2) but somewhat more than that, hence the need for a formula - which is a bit complicated, (http://design.ae.utexas.edu/mission_planning/mission_resources/orbital_mechanics...) yet doable on a scientific pocket calculator.
I did that before computers were publicly available.
Way better: a computer programme or an online calculator.
If you work in a limited area, a simple list of sat names and AZ/EL settings printed out and laid in the box of your sat meter is enough.
If you can, make pictures of the spectrum displays of the sats you use most (if your sat meter has a spectrum display function), and get a compass and a protractor (inclinometer). (Google for "mini electronic protractor").
For a given dish, once pointed, the inclinometer will give you an angle that you can copy to the next (identical) dish when held against a specific part of the AZ/EL mount, no matter what the difference between that angle and the real inclination is.
On the tooway dish, the rear face of the "pan" that holds the reflector is exactly 90 degrees from the elevation angle, so for 34.4 elevation, your inclinometer reads 90-34.4=55.6.
To pre-point a dish quite exactly in azimuth, rather than trying to point it with a magnetic compass while standing right behind the (steel) mount, where the compass is deviated and rather shows you where the steel pole is (that we know, after all!), walk away in front of the dish and point your compass to the azimuth needed minus 180 or plus 180, like: wanted azimuth 165 (smaller than 180), make it 165+180=345 (a bit west from due north, that is. Aim over your compass (best is to have a hiking compass with a mirror-sight on it), and check if the LNB arm is in line with your inverted line of sight, while you are far from the steel parts. With this method for EL and AZ per-pointing, I could get Ka-Sat on the first try and almost dead-on in some cases.
If the sat is not found by then, you might need to sweep *slowly* left and right from the wanted azimuth, every time with small changes in Elevation, start with a bit higher elevation than actually needed (oftentimes, sat mounts and poles tend to sag down under the weight of the dish, check, but don't presume that your pole is 100% vertical)
For this searching, a spectrum display on the sat meter is helpful, as is a built-in indentificator of the sat (which can be wrong at times), but it is not 100% necessary ti have.
Be aware of the fact that on digital signals, the meter or receiver needs some time to lock on the signal clock, so if you sweep the sky too fast, you can miss the sat you look for, and you have to start over with a pre-point. Take your time.

Good luck everyone
(sometimes you need luck: I got a cheap customer's dish only pointed correctly after trying for quite a while because it slipped out of my hand and tipped down really far, and found the sat by itself - it just had very a weird (big) offset angle!)
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