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Jul 22nd, 2008 at 2:44pm
The most important precaution regarding any satellite is not to transmit unless you are in phone communication with the hub who are watching for your low level carrier on a spectrum analyser, to verify if you are on the correct satellite, and on exact polarisation angle and frequency.
At low elevation angles particularly, you should take local precautions to avoid people getting themselves into the beam to the satellite. I can think of other important precautions, like avoiding dropping tools on people below. So wear a hard hat (applies to people on the ground also), tie off ladders etc.
I can't think of any precautions peculiar to Telsar 12.
If the question is about link budgets then read on...
Use this satellite range calculator to find the range=39900 km approx from you to the satellite.
Use this https://www.loralskynet.com/pdf/telstar12_pamphlet.pdf to find the uplink satellite receive G/T = + 2.6 approx.
Note the uplink PFDsat for the various gain serttings. Note the downlink saturated full transponder eirp also. You will need to take off the output back off and subtract 10 x log(carrier bandwidth/transponder bandwidth)
Using the above calculate uplink satellite link budget to give you an idea of what C/Nup is possible at the satellite using various carrier bandwidths. Does it look feasible ?
Contact the satellite operator to find where there is spare transponder capacity on whatever beam to beam inter-connectivity you want, e.g. Europe to Europe, Europe to US etc.
Find the transponder gain step setting for the particular up beam to down beam configuration and the satellite operators desired operating point (i.e. Back off in versus Back off out, for multicarrier operation)
Determine the downlink eirp, by proportion of the whole transponder, for whatever uplink pdf you can create. Input your idea for hub receive dish size, location of hub in downlink beam etc. Estimate some uplink and downlink interference, plus transponder intermod interference (normally -21 dB) and you have your answer in terms of overall C/N for a some chosen carrier bandwidth.
Now review what your iDirect return link hub burst receiver needs in terms of Eb/No and C/N (I don't know the modulation method and FEC options.) This Eb/No calculator may be of use. Apply some suitable rain margin (say 5 dB) and the result is what you want.
Maybe someone already operating to Telstar 12 with iDirect can say what is their experience of uplink bit rate, hub burst receive Eb/No and rain margin for dish size and BUC power rating.
wxw
Best regards, Eric.
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