dear Sandeep,

The digital broadcast satellites are geosynchronous satellites and therefore they are very distant from the earth. Also, they made to cover relatively large area on ground surface to service more customers.Since the satellite link is a wireless microwave link and the base band signal is digital and the carrier is in form of sine wave one can use a digital modulation technique such as FSK, PSK, and QAM. As the satellite link is power limited and we have to realize certain minimum to noise ratio one uses preferably modulation techniques that trade bandwidth for power, ie with larger bandwidth such as Fsk ,BPSK and QPSK. One decided for QPSK for its superior transmission performance.

For more details see the LINKhttp://www.img.lx.it.pt/~fp/cav/Additional_material/Satellite%20Direct-to-Home.pdf

Thank you for your question

thank you for such a nice explanation ... I would like to ask one more thing - since DTH is a satellite communication, there is a delay at reception (TV) e.g. when we compare this received signal with one received via cable operator (service provider not using DTH) .. is this a disadvantage of DTH (consider a case of live cricket match where you will see a delay of 2-3 balls)

dear Sandeep,,

You are welcome!

The broadcast system is a simplex system. It is a one way transmission, All packets will be delayed by the same amount of time and the receiver will not be annoyed by the constant delay. Constant time delay of the signal will not affect its observation. Are you annoyed during observing any satellite tv program?

Wish you success.

One hop delay from a transmitter on earth to satellite and back to a receiver on earth is about 250 ms (quarter second) as the two way distance is about 72000km. This delay is tolerable even for voice communication via satellite and DTH being a broadcast service it will not be perceived at all.

thank you Abdelhalim Zekry Sir, Rn Mutagi - we can tolerate this delay in some cases but you cannot tolerate it if you are watching something live e.g. cricket match (i have experienced a delay of 2 balls)

This may be due to differing delay in the electronics especially the video codec. It may take different times to decode the video blocks depending on the motion of objects in the seen. In order to observe the absolute delay you have to observe the original and the received signal simultaneously.You only watch one signal the received signal. In principle, there are other causes of delays due to mismatch between the receiver and antenna and due to multiple images because of multiple reflections.

Thank you.

thank you - Abdelhalim Zekry sir