Question 1: Describe the given terms:
a) Ground waves.
b) Space waves.
c) Sky waves.
Question 2: Why can’t the:
a) Ground waves
b) Space waves and
c) Sky waves are sustained for long distance communication beyond 10 to 20 MHz?
Question 3: What do you mean by the term critical frequency for sky wave propagation? Write down an expression for the critical frequency in terms of the maximum electron density of the ionosphere. Determine the range of variation of frequency for this critical frequency?
Question 4: Define the word ‘critical frequency’ in relation to sky wave propagation of electro-magnetic waves. On a specific day, the maximum frequency reflected from the ionosphere is 10MHz. On another day, it was found to reduce to 8 MHz. Compute the ratio of the maximum electron densities of the ionosphere on the two days.
Question 5: Draw a block diagram of a simple amplitude modulation, describing in brief how amplitude modulation is accomplished.
Question 6: What does the method of detection of amplitude wave mean? The amplitude modulated carrier wave of angular frequency ωc, (ωc - ωm and ωc + ωm) and (ωc - ωm), where ωm is the angular frequency of the modulating signal. Describe, in brief, with the help of a block diagram the necessary details of a simple method used for ‘detecting’ the modulating signal from this modulated carrier wave.
Question 7: A transmitting antenna at the top of a tower has a height 32 m and the height of the receiving antenna is 50 m. Find out the maximum distance between them for satisfactory communication in LOS mode? Given that radius of earth is 6.4 × 106 m.