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SatmasterPro MK8.X Csat/XPI

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Ex Member
Ex Member

Jan 18th, 2012 at 8:48pm  
In SatmasterPro MK8.X, what would be the Csat/XPIo value of a 18 MHz balanced carrier received by antenna with VAR = 1.3 (17.7dB) on a 72MHz transponder with IBO of 5.5dB, OBO of 3.5dB?


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Eric Johnston
Senior Member

Posts: 2109
Reply #1 - Jan 18th, 2012 at 10:49pm  
Does this help: https://www.satsig.net/axial.htm ?

The relative levels (eirp down of all signals in the relevent bandwidth) of the co-pol and cross-pol carriers are  important. If the co-pol (wanted) signal power spectral density is low level from the satellite and the cross-pol interferer is high level then you need extra good x-pol isolation.

The transponder bandwidth, input and output back off are of no relevance.  It might happen however that the cross-pol transponder is operated with a single giant carrier at -0.5 dB output back off while the wanted co-pol is operated -in multicarrier mode, backed off by -3.5 dB, in which case you need extra good cross pol isolation.

When you do the link budget the overall C/N is basically the addition of all the components:
C/N = C/Nup + C/Iup +C/intermod + C/N down +C/I down.

This will add them up for you: https://www.satsig.net/linkbugt.htm

Try to improve your C/I down. 17.7 dB is awful.  30 dB excellent.  

Some cheap receive-only C band circular polariation feeds had 17 dB XPI in the FM TV days when interleaving of the co-pol and cross-pol FM carrier centre frequencies reduced the interference effect. Unfortunately with digital carriers interleaving does not help and it is the total of the interferers in the receive bandwidth that matters.

Best regards, Eric
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« Last Edit: Jan 20th, 2012 at 3:44pm by Admin1 »  
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Ex Member
Ex Member

Reply #2 - Feb 8th, 2012 at 7:16pm  
Dear Eric,


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