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MULTI BEAM ISSUE

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akki
Ex Member


Apr 4th, 2012 at 11:11am  
Dear Mr.Eric

We have VSAT Hub transmitting on Intelsat 12 via europian beam on V pol. Our remote is on Middle east beam. the satellite is Xpol. As per rule we have to rcevive on H pol and transmit on V pol from remote but we have V POL given by intelsat on middel east beam so in that case we have to receive on V pol . But we have 2 port cross pol feed .
What will be the solution for this should we go for 4 port feed or co-pol feed or request intelsat to change tranponder pol for us please advice..
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Eric Johnston
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Reply #1 - Apr 4th, 2012 at 2:31pm  
Co-pol operation (i.e. transmit and receive on the same polarisation) is very unusual and it is far more likely that you are to operate cross-pol in both the Europe and Middle East beams.  Try to avoid co-pol operation as it needs a special diplexer instead of OMT and your network will not be able to be transitioned easily to any other normal satellite.

Look at the documentation provided to you by Intelsat and clarify what you are to do. Talk to them.  If they insist on co-pol operation point out the problem this causes you with your remote sites. Maybe there is some price discount for such awkward polarisation configuration !

Your VSAT hub is in the IS-12 Europe beam and you are transmitting on Vertical polarisation.  At the hub, you will not be able to see your hub uplink signal, as the signal will come down in the Middle East beam.  You might ask Intelsat to verify that your hub uplink carrier has the correct frequency, bandwidth, power and polarisation.  Intelsat have a cooperative monitoring teleport earth station in the Middle East down beam. Turn the carrier on and off to check so they know it is yours.  Also get them to check that your polarisation angle is perfectly adjusted.  The actual angle, after adjustment, will be tilted significantly.

At your remote site in the Middle East, find the outlink carrier from your hub station.  It does not matter if this is Vertical or Horizontal.  Horiziontal down is more likely.   Just do as told.  The cross strap switches on the satellite can be configured anyway, on  whole transponder basis.  Adjust the remote receive polarisation angle and get this one way link working well.

If Intelsat confirm that you are to operate cross-pol at the remote site,  talk to Intelsat and turn on the uplink from the remote site at low level and in CW (unmodulated) mode.  Your hub station, and an Intelsat monitor station in the Europe beam, should immediatly see a tiny spike at the correct return link frequency. The spike should, obviously, appear in an empty part of the transponder.   Intelsat will check your cross-pol level and may ask you to adjust the remote site polarisation angle slightly. Gradually increase power and add modulation under instruction from Intelsat.

You mention 4 port feed.  It is helpful at your Hub station to have dual port polarisation receive, as you will be able to look on the opposite receive polarisation, and if this is clear, you will be able to measure cross-pol levels from your remote sites and assist in line ups.  Similarly, you can observe cross-pol traffic if you think you are suffering from cross-pol interference into your service.

Best regards, Eric.
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akki
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Reply #2 - Apr 4th, 2012 at 3:00pm  
Thanks Mr.Eric for your instant reply.

We have done CPI test from remote but as we received good isolation our receive go bad and when receive get better isolation go bad. This is due to multibeam and the transponder polarity they provided us which is V in middle east for receive and V for transmit in euro beam. they told us to get 4 port feed. I think it will cost us or what about co-pol feed can we also use.

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Eric Johnston
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Reply #3 - Apr 4th, 2012 at 7:13pm  
Ask Intelsat:

What is your uplink polarisation in Europe?
What is your downlink polarisation in Europe?

What is your uplink polarisation in Middle East?
What is your downlink polarisation in Middle East?

Put the 4 answers here.

I don't understand "due to multibeam"

You will need either 2 port cross-pol or 2 port co-pol feed.

4 port is not necessary, unless your teleport hub is to transmit and receive on both polarisations, for example for multiple hosted VSAT network hubs.

Best regards, Eric.
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