The use of ionospheric reflection of radio waves for long-distance communication has, to a great extent, been replaced by satellite communication.

Question 2

The use of ionospheric reflection of radio waves for long-distance communication has, to a great extent, been replaced by satellite communication.

(a) State and explain two reasons why this change has occurred. [4]

(b) The radio link between a geostationary satellite and Earth may be attenuated by as

much as 190 dB.

Suggest why, as a result of this attenuation, the uplink and downlink frequencies must

be different. [2]

Reference: Past Exam Paper – June 2011 Paper 42 & 43 Q11

Solution:

(a)

Any 2 sensible suggestions:

Examples:

Unreliable communication because the ion layers vary in height / density

Cannot carry all information required since the bandwidth is too narrow

Coverage is limited since reception is poor in hilly areas

(b)

The signal must be amplified (greatly) before transmission back to Earth.

The uplink signal would be swamped by the downlink signal.