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Direct Link To This Post Topic: VSAT Installation & Training
    Posted: 14/August/2008 at 21:30

VSAT Installation Tutorial

A Tutorial on VSAT Installation.

When chosing a site for a VSAT installation, the antenna needs to be located with a clear view to the satellite. Access to the antenna should be restricted to prevent any damage or harm from occurring to either the antenna or people. Ideally, the antenna should be sheltered from wind.

The outdoor unit (ODU) is mounted on the feed arm in front of the antenna and houses the Radio Frequency (RF) equipment required to transmit (TX) and receive (RX) from the antenna.

 

The outdoor unit (ODU) mainly consists of these devices:

  • Low Noise Block (LNB) which is a down converter and receiver
  • Block Up Converter (BUC) this is the up converter and transmitter
  • Ortho-Mode Transducer (OMT) the Tx and Rx waveguide joint.
  • Microwave filters which protect the LNB from the Tx signals.

 

Safety Is Important:

Installing a VSAT can be very dangerous especially on a roof. Follow the instructions carefully to ensure that the antenna is correctly assembled.

Care must be taken when working near the edge of roof tops such that you do not fall off or drop anything on people who may be below. Never work alone and always look out for each other.

Click Here to download the PDF format RF Radiation Hazard sign.
 

Static - Permanent Mounting:

This type of installation is usually a pole mount which is bolted securely to the ground. The pole can be concreted into a hole but in both cases must be completely vertical.

 

Temporary Mount (Non-Penetrating):

This is a quickly deployed mount which consists of a frame constructed to hold the pole vertically and securely whilst providing a large base for the addition of ballast. Ballast (heavy bricks or concrete) weigh down the mount preventing the wind from overturning the antenna assembly. In extreme conditions even a permanent mount can sustain damage and so a sheltered location and saftey lines attaching the mount to the building should be considered. The antenna could otherwise be blown of the roof of a building. A structural survey is required before any such mounts are installed on a roof to ensure the weight is not a risk to the building.

 

Tx & Rx Coax Cables:

Usually two coax cables carry the signals between the IDU and the ODU. Power for the LNB and BUC as well as control signals are carried along these coaxes.

Ensure that the ends of the coax cables are properly terminated in F type connectors.

There should be 2mm of copper coax centre conductor protuding from the connector in order to ensure a good connection is made.

The braided screen of the coax cable must not touch the inner copper conductor. This will cause a short and damage the equipment.

Connect the coaxes to the ODU noting which are Tx and Rx then run them to the IDU.

The connectors at the ODU should be sealed against the weather with the cables dropping down from the connectors before being taped up to the feed arm. This allows water to harmlessly drip from the cable rather than run into the connector, in other words the connectors should be higher than the cables.

 

The indoor unit (IDU):

The indoor unit (IDU) usually consists of a single box which should be located in a dry, cool and clean place. An office environment is ideal.

The coax cables run from the antenna ODU to the IDU and should not cause a hazard to anyone along the way.

Use cable ties to clip them safely to pipes, fencing or similar in order to make the installation neat, tidy and safe.

Cables that can blow around in the wind will fail long before cables that are securely tied down.

The IDU requires a stable mains supply and connection to the end user equipment. This could be further units for telephone exchanges or networks for internet or intranet connections.

VSAT Antenna Pointing & Set Up:

Antenna Azimuth & Elevation Calculation


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.
 
Pointing the antenna is not easy but can be acheived with a compass and the required angles. (Azimuth and Elevation)

Azimuth is the angle bearing from True North. (North = 0 degrees)

Satellites are often listed as a bearing from South, but this is the Longitude of the satellite orbit. For example, 53 degrees East (53E) means that the satellite is over the equator because there is no Latitude given (0 degrees is the equator) and the 53 degrees is the angle from South in this case East. (South is 180 degrees). East means that the angle is 180 - 53 = 127 degrees. This then is the approximate Azimuth of the satellite with a Longitude of 53 deg East if you are in the Northern hemisphere around the Greenwich Meridian (0 degrees Longitude). If you are east or west of the Greenwich Meridian then this also changes the angles to the satellite.
 
It is sometimes forgotten that below the equator, the azimuth angles are different, instead of looking south you would look north to the equator.
 
Elevation is the angle up from the horizon. (Horizontal = 0 degrees)
 
The final step is done whilst communicating with the VSAT network 'HUB' staff and they will ask to adjust the polarisation by rotating the feed.

Whilst doing this do not stand in front of the antenna, it is transmitting RF radiation for one thing and your body will block the signal to the satellite for another. Stand to one side and adjust feed in small degree steps until the HUB or NOC is happy.

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 teh 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. 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 th elocation 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.

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. Obvioulsy, this is only of use if you are pointing a TV satellite antenna.

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:

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.


VSAT Installation and Training Videos:

 
 
 
Additional Information:
 
 
 
 
More Tutorials & Guides:
 
 
 
 
 
 
 


Edited by Satcoms UK - 16/April/2015 at 22:46
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