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Satellite Antenna Pointing & Set Up

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    Posted: 22/October/2008 at 18:41

Antenna Pointing & Set Up:

Course 6 covers the Installation of VSAT antennas. Click Here to skip Course 6.
 
Antenna Azimuth & Elevation Calculation
 
To determine the required angles from your location to the satellite you wish to point at, try the Tools page for an online Azimuth & Elevation Calculator and links many others.
 
Just enter your latitude and longitude and select the satellite then click 'Go' and the answers are displayed in a Google Maps display of your location.

Find the Satellite:

Set the antenna elevation angle using an inclinometer, or by using the scale on the antenna, as accurately as you can to the elevation of the desired satellite. Lock in position but make sure that you can still move the antenna left and right in Azimuth.

Determine your latitude and longitude on the earth by using a GPS reciever or by estimation using a mapping website. See http://www.ukmsf.org/GMaps/FindMe.htm

To find the correct satellite you will ideally have a satellite meter or a spectrum analyser.
 
Inexpensive signal meters will give an increased level reading as you pass each satellite. They do not identify the satellite you are looking at as you pass it or point up on it.  If you can identify a known satellite with such as device then you will have found a reference satellite. The satellite you want can then be found by looking up the angles for the reference satellite and adjusting the antenna accordingly from this position to the angles for the satellite you actually want.

 
These are often available on eBay - see our Shop for some possible 'SatFinders' for sale.
 

By Using a Spectrum analyser:

Spectrum analysers are far better but much more expensive and require more expertise to set up and use.  Care must be taken not to apply a DC signal to the analyser as this can cause a lot of damage to an already expensive peice of equipment. The cable from the antenna may have DC on it and so you must first be sure that it is safe before plugging into an analyser.

You will need a supply of DC voltage and possibly a 22kHz tone.  The receiver can provide these up the coax cable. An RF coupler with a DC block on one side is invaluable and is connected inbetween the receiver and the dish.  The DC block side is to be connected to the analyser.
 
The analyser can display the signals being received in a particular band of frequencies. Recognising these signals is key to finding your desired satellite. Again, it helps if you already know the location of a good reference satellite and can clearly see the signals being received from it. In my experience satellites are found mcuh more quickly with a spectrum analyser tuned to look at a known signal for a known satellite than by using a signal meter.
 
You may not recognise the signals but if you are receiving signals then you can peak up on them to get the maximum signal strength and the biggest signals. then you can see if the receiver is getting what you expected.

By Using a Satellite TV receiver:

The TV receiver (for example a Sky DigiBox) can provide you with signal quality and level information. This is displayed as bar graphs on the TV. Not so useful if you are up a ladder but with the help of someone else you can be told if the signal levels are getting better or worse. If you can see the TV by putting it outside then even better. I have used an RF wireless portable TV attached to the Rf out of a Skybox to be able to see the screen when up the ladder and this was very useful.

Peaking up:

Start with the azimuth and move the dish from one side of the satellite through the main signal and out the other side untill you lose the signal.  Peaking th esignal simply means finding the maximum signal strength which is known as the boresight of the satellite. Pointing directly at it. The Azimuth is only the first part however and so on to the next.

Elevation is done in the same way and there may be no actual increase if by chance you already have the antenna on boresight.


Antenna Polarisation Setup:

(Not necessarily required for some TV satellite dishes such as Sky mini-dishes)

Before alignment of the antenna with the satellite, the polarisation should be setup correctly.  The polarisation is the axial rotation of the feed system (Feed horn/LNB/BUC) on the antenna. 

Polarisation Setup - Step 1:

Loosen the feed assembly slightly to allow slight rotation by hand.

Set the polarisation to the nominal position.

Polarisation Setup - Step 2:

Rotate the feed assembly based on the results of the antenna angle calculation (see below). Facing the satellite a positive rotation is clockwise and a negative rotation is anti-clockwise.

Polarisation adjustment normally needs assistance from the NOC.  The NOC can make your antenna system transmit a continuous wave (CW) on a frequency where it is unlikely to cause interference.  The NOC uses a spectrum analyser to monitor this signal and detremine the polarisation and may ask you to make adjustments to the feed. This should be done in very small amounts leaving about 20 seconds between each small turn of the feed so that the NOC can measure any difference.

Click Here for Next Tutorial 



Edited by Satcoms UK - 16/April/2015 at 22:42
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