Question

A ground receiver receives a signal at 5 MHz, transmitted by a ground transmitter at a height of 320 m, which is 110 km away from it. Then it can communicate through (radius of earth \(R = 6400\,km\))

• A. space waves
• B. ground waves
• C. sky waves
• D. both sky and ground waves
• E. sky waves, ground waves and space waves

Hint:

2–30 MHz → ionospheric reflection → sky wave.

Answer 1

The Correct Option is C

Concept: Different propagation modes:
• Ground wave: low frequency (<2 MHz)
• Sky wave: 2–30 MHz
• Space wave: line of sight

Step 1: Check frequency. \[ f = 5\,MHz \] → lies in sky wave region.

Step 2: Check distance. 110 km exceeds typical ground wave range.

Step 3: Check line of sight.
Height is small → LOS distance insufficient.

Step 4: Conclusion. \[ \boxed{\text{Sky wave}} \]