Satellite Communications/Bandwidth

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Question
Dear Sir,I have a question about the bandwidth of Dvb s modulator and upconverter. I usually read on product specifications that IF bandwidth is 40 or 80 Mhz depending on the If frequency of the modulator or upconverter(70 or 140 Mhz).What I do not understand is whether the bandwidth only depend on the input Signal or it is due to construction design and if the latter is True which element in the modulator or upconverter is limiting the bandwidth to the 40 or 80 Mhz values?
Thanks and regards
Mauro

Answer
Hi Mauro,
The Bandwidth specifications are always related to MODULATION METHODS and Digital techniques use a figure with Bit rate to decide what should be available band with in the medium that do not distort the quality of the Video. Modulator decides what is the maximum bandwidth it can use for deviating the base band compressed signal.  UP CONVERTER is used ONLY to enable the signal to interface with PHYSICAL LAYER in digital networking Layered Protocols. U/C has no roll in deciding bandwidth specification.
Also your doubt about dependence on Modulating signal is also NOT right, Bandwidth depends on TYPE OF MODULATION ONLY. The parameter contributing to BW in modulator is: number of side bands that are generated while modulating/ MAXIMUM DEVIATION at which the MODULATOR works in its linear characteristic,that means,  frequency response of the Modulator.
Cheers/GTRao

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TIRUMALA RAO G

Expertise

Satellite Communications Applications, Link Calculations, Teleports, Earth Stations,VSAT, Tracking, Mobile Communications, Next Generation Networks.

Experience

40 Years. Indian Space Research Organisation, PANAMSAT, Satellite Based VSAT Networks, IP Networks.

Organizations
ISRO, PANAMSAT, Engineering Institution for Higher Education (GVP College of Engineering), Consultancy.

Education/Credentials
Graduate in Electronics and Communication Engineering with Distinction. Guiding scholars for their Doctoral thesis in related areas in Academics.

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