How to align iDirect VSAT to PakSat1 tutorial.

Written by Tom on Monday 02/04/07


What you will need over and above the VSAT equipment:

C Band receiver.

Free to air TV decoder and TV.

Laptop with iSite installed on it.


The PasSat1 satellite is in a geostationary orbit at 38° East Longitude, and carries high power payloads in both Ku and C bands.


Longitude is given as an angular measurement ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. ( the Greenwich meridian as the universal prime meridian or zero point of longitude.)


Background provided by Peter Van then man.


A geosynchronous satellite is made to orbit
so that it is always directly over a certain place on the globe. Any
satellite that we use a fixed dish to communicate with is
geosynchronous (two examples of non-geosynchronous satellites are GPS
and iridium, both of which have low, fast orbits that mean a certain
satellite is never overhead for long). Iridium and GPS are both
designed for small dishless receivers (Iridium is the global cell
service that works anywhere in the world and is also rather
expensive). It turns out that it is impossible to have a
geosynchronous satellite that orbits above any point except the
equator.


So, all geosynchronous satellites are above the equator, AND they are
all orbiting at exactly the same height. This is because the speed of
the orbit increases as the distance from earth of the orbit decreases
(and vise versa). Satellites that are really close to earth just fly
around it--very quickly. Geosynchronous satellites are way up there
(hence the need for a dish) and move slow enough to stay exactly above
a certain point on the equator.


Now, if all the geosynchronous satellites are above the equator and at
the exact same orbital height, you really only need one number to
describe a satellites orbit: the longitude that it is parked above.
The problem of aiming is then only a three-dimensional geometry
problem--but a complex one. No two places on earth will aim in the
same exact compass direction and elevation angle to get PakSat1.
There are online calculators that will do it for you if you know your
own longitude and latitude on earth. A good one is:
http://www.satsig.net/ssazelm.htm. Most calculators only give you an
azimuth (compass direction) relative to true north, but this one is
cool because it also calculates the magnetic offset for you (which is
different in different parts of the world).


Step One:

Using the calculator find out approx where to point the satellite dish.


Step Two:

Get a course fix on the free to air TV. From this link you can find a list of frequencies allocated to different TV stations. These are C band frequencies. Program you TV receiver to the correct frequency and move dish incrementally in a up-down-across motion until the TV channel is received.


Step Three:

Change the C Band receiver for the VSAT transceiver. Connect the iDirect router to the LNB and plug in the laptop to the iDirect LAN socket with a cross over cable. Using the iSite (iSite is made by iDirect and monitors the IDirect router download from here) application select "Antenna Pointing" from the top Tool Bar and then select the "Antenna Pointing" tab. At this stage you should have the Tx cable to the BUC disconnected. WARNING: Only disconnect cables with the iDirect router powered down.
Click start and then OK to the warning dialogue. It takes several second for the system to register. By fine tuning I could get 15
volts in the "Current Signal Strength".


Step Four:

File->Settings and Statistics->View and check the Downstream SNR box. I have been told that the best you can get here is +10 and that +7 is nominal.


If you get a Current Signal Strength of 14v or greater and a Downstream SNR of 7 or greater you should be in business.