Distinguish between 'sky waves' and 'space waves' modes of propagation in communication system.
(a) Why is sky wave mode propagation restricted to frequencies upto 40 MHz?

Explanation

### Step-by-Step Solution:

1. **Definition of Sky Waves**:
- Sky waves are radio waves that are transmitted towards the sky and are reflected back to the Earth by the ionosphere. This mode of propagation allows communication over long distances by bouncing signals off the ionosphere.

2. **Definition of Space Waves**:
- Space waves, on the other hand, are radio waves that travel directly from the transmitting antenna to the receiving antenna. This mode of propagation is typically used for line-of-sight communication, such as in television and radio broadcasting.

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