Distinguish between sky wave and space wave modes of communication. What is the main limitation of space wave mode? Write the expression for the optimum separation between the transmitting and receiving antenna for effective reception of signals in this mode of communication.

Explanation

### Step-by-Step Solution

**1. Distinguish between Sky Wave and Space Wave Modes of Communication:**

- **Sky Wave Communication:**
- **Transmission Method:** Sky waves are transmitted by ionospheric reflections. They reflect off the ionosphere, allowing them to cover long distances.
- **Frequency Range:** Typically operates in the frequency range of a few megahertz (1-2 MHz) to about 30-40 MHz.
- **Propagation:** These waves undergo total internal reflection at various layers of the ionosphere, which helps in long-distance communication.
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