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Revision questions

Question 1 - The Surrey satellites transmit signals at and at a frequency of 430 MHz (430,000,000Hz). What is the wavelength of these signals? Answer Explain

Question 2 - The Surrey satellites' signals are detected 3000 km away on Earth. How long does it take the satellite's signal to travel to Mission Control? Answer Explain

Question 3 - Satellite television signals travel from the transmitter on Earth, to the satellite and then down to the receiver on earth. If the satellite is in geostationary orbit at an altitude of 36000 km, how long does the signal take to get to the receiver after it is first transmitted? Answer Explain

Question 4- Outline the difference between digital and analogue signals. Use a diagram to help your explanation. Why are digital systems considered preferable? Answer

Question 5 - For transmission, signals are added to a carrier wave. This is termed modulation. Explain the difference between amplitude modulation and frequency modulation of an analogue signal. Answer

Question 6 - Digital signals undergo Pulse Code Modulation. Explain briefly what this is. Answer

Question 7 - Surrey satellites typically use Frequency Shift Keyed Modulation. Explain briefly what this is. Answer

The information carried by the carrier wave changes its frequency so there has to be a range of frequencies - the bandwidth - to carry the signal. A bandwidth of 10 kHz will carry up to 10000 bits per second (1 Hz bandwidth per bit of information).

Question 7(a) - In practice the bandwidth has to be broader than this because of the Doppler effect. Explain how the Doppler effect changes the satellite's signal. Answer

Question 7(b) - A common transponder bandwidth on a satellite is 72 MHz. What bit rate can these transmit, in theory, if the Doppler effect is neglected? Answer

Question 7(c) - If the transmission frequency of this satellite is 430 MHz what range of frequencies does it actually transmit taking into account the required bandwidth? Answer Explain

Question 8 - Explain what noise is in the context of satellite signals. What does Surrey Satellite Centre (Mission Control) do to check whether the signal has been corrupted by noise? Answer

Question 9 - If a datafile from a satellite consists of 50 million bits of information and is transmitted at 430 MHz with a bandwidth of 65 MHz. How long does the data file take to be transmitted? Answer

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