# Antennas Questions and Answers – Virtual Height

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Virtual Height”.

1. The effective height of a layer of ionized gas in the atmosphere by which the radio waves are reflected around earth’s curvature is called Virtual height.
a) True
b) False

Explanation: The height to which a short pulse of energy is sent vertically upward and traveling with the speed of light would reach taking the same two-way travel time as does original pulse reflected from ionosphere layer is called the virtual height.

2. Relation between skip distance d, virtual height d and MUF fMUF is ______
a) $$d=2h\sqrt{[\frac{f_{MUF}^2}{f_c^2}-1]}$$
b) $$h=2d\sqrt{[\frac{f_{MUF}^2}{f_c^2}-1]}$$
c) $$d=2h(\frac{f_{MUF}^2}{f_c^2}-1)$$
d) $$h=2d(\frac{f_{MUF}^2}{f_c^2}-1)$$

Explanation: Relation between skip distance d, virtual height d and MUF fMUF is given by
skip distance $$d=2h\sqrt{[\frac{f_{MUF}^2}{f_c^2}-1]}$$

3. Find the skip distance when the angle of incidence is 200 and virtual height is 50km?
a) 13.22m
b) 13.22km
c) 36.33km
d) 36.33m

Explanation: Skip distance $$d=2h\sqrt{[\frac{f_{MUF}^2}{f_c^2}-1]}=2h\sqrt{[secθ_i^2-1]} =2×50×\sqrt{[(sec20)^2-1]}$$
d=36.33km

4. The differences in the virtual height and actual height are affected by the electron density in the ionosphere region.
a) True
b) False

Explanation: The difference occurs due to the exchange of energy between wave and the electrons present in the ionosphere which changes the velocity of propagation of wave. So the difference between virtual and actual height are influenced by the electron distribution.

5. Find the virtual height h when the angle of incidence is 600 and distance of separation 120km.
a) 60km
b) 64.34km
c) 34.64km
d) 72.42km

Explanation: Virtual height $$h=\frac{d/2}{\sqrt{secθ_i^2-1}}=34.64km$$

6. The height at a point above the earth’s surface at which the wave bends down to the earth is called ______
a) Actual height
b) Virtual height
c) Skip distance
d) Distance of separation between transmitter and antenna

Explanation: The height at a point above the earth’s surface at which the wave bends down to the earth is called actual height or true height. Virtual height is greater than actual height. Skip distance is the distance the wave travels from the transmitter to the receiver without touching the ground.

7. Skip zone is distance between the point where the ground wave reception becomes zero and the sky wave returns for the first time.
a) True
b) False

Explanation: The Skip zone is the region between the point where the ground wave reception becomes null and the sky wave returns for the first time. It entirely depends on the ground wave coverage and the skip distance. 