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DVB-S on C-band

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geokant
Ex Member


Oct 20th, 2011 at 11:42am  
Hi all,

Firstly, I'm a newbie in this forum so I wish I have not repeated this topic, but I am on an urgent situation. My problem is:

I have to install an VSAT system to W2A Satellite and I have only an spectrum analyser which is available to work in DVB-S modulation. The material is, an 2.4m antenna, LNB works between 3.625 to 4.200 Ghz., I checked to perform pointing with this analyser, every freq. list existing in websites, but I didn't find any commercial transporder available in DVB-S modulation in this range of spectrum.

I was thinking to change LNB to ones of Ku band but this feed horn is only available to C band LNBs...

Anybody has an idea?

Thanks inadvance for your help, and sorry for my english because it is not my native language.

Kind regards,
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USN - Retired
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Reply #1 - Oct 20th, 2011 at 12:06pm  
A satellite transponder is merely an orbiting radio repeater, it has no modulation type of its own. The modulation type is originated by a modem at one ground location, sent to the satellite where the signal is amplified and the frequency is changed, then sent back down to another ground location that has a modem configured to the same originating modulation type.

Perhaps you are looking for a VSAT provider that sends a DVB-S modulated signal to the satellite. If this is the case, what type service are you attempting to install? Or does your installation involve leasing transponder space through which two or more ground stations must connect? And is there any binding reason that you must install via W2A? Or could you establish the desired service through any C-band satellite within view?

//greg//
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Reply #2 - Oct 20th, 2011 at 12:33pm  
Lyngsat has information about carriers on satellites:
see http://www.lyngsat.com/ew2a.html

In the case of Eutelsat W2A, C band, these is a distinctive group of three STARTIMES TV carriers:
3914 MHz, SR=12.1Msps
3930 MHz, SR=12.5Msps
3948 MHz, SR=16.2 Msps

If you have a C band LNB with local oscilaltor 5150 MHz then the above carriers will appear in the L band cable at the following frequencies
5150 - 3914 = 1236 MHz
5150 - 3930 = 1220 MHz
5150 - 3948 = 1202 MHz

So look for this group of 3 carriers on your spectrum anlayser. Note they are inverted.

To find the wanted satellite set the elevation angle accurately and then swing the antenna boldly sideways to find a satellite. Have the spectrum analyser span set initially to 950-2150 and you will see something.  Peak up and record (measure and mark) the az and el adjusters very accurately so you can always get back to this initial found satellite.

If the 3 carriers don't match try the adjacent satellites either way along the orbit.  If no good, change the polarisation.  Undo the OMT to polariser junction and reattach 90 deg different, i.e. 45 deg the other way from the line of pins/slots inside the polariser.

Best regards, Eric.
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