# Antennas Questions and Answers – Space Wave Propagation – Line of Sight Distance

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Space Wave Propagation – Line of Sight Distance”.

1. Which of the following statement is defined as line of sight distance?
a) Distance covered by a direct space wave from transmitting to receiving antenna
b) Distance covered by an indirect space wave from transmitting to receiving antenna
c) Distance covered by a direct sky wave from transmitting to receiving antenna
d) Distance covered by an indirect sky wave from transmitting to receiving antenna

Explanation: LOS (Line of sight) is defined for space wave propagation. It is the distance covered by a direct space wave from transmitting to receiving antenna. It depends on the height of the transmitting and receiving antennas and effective earth’s radius factor k.

2. On which of the following factors does the LOS distance depends?
a) Height of receiving antenna alone
b) Height of transmitting antenna alone
c) Only on height of transmitting and receiving antenna
d) On height of transmitting and receiving antenna and effective earths radius factor k

Explanation: LOS (Line of sight) is the distance covered by a direct space wave from transmitting to receiving antenna. The LS distance depends on the effective earth’s radius factor k and height of the transmitting and receiving antennas. The LOS distance is given by $$d = 4.12(\sqrt{h_t}+\sqrt{h_r})$$ in km.

3. Which of the following order is correct?
a) LOS > Radio horizon > Optical horizon
b) Radio horizon < LOS < Optical horizon
c) Radio horizon > Optical horizon > LOS
d) Optical horizon > Radio horizon > LOS

Explanation: Radio horizon is the point to which a space wave can reach maximum and is greater than optical horizon. LOS is thedistance covered by a direct space wave from transmitting to receiving antenna. If distance between antennas is less than LOS then it is referred as Optical horizon and is approximated to LOS.

4. Expression for the LOS distance is _____ (km)
a) $$4.12(\sqrt{h_t}+\sqrt{h_r})$$
b) $$4.12(\sqrt{h_t}-\sqrt{h_r})$$
c) $$3.56(\sqrt{h_t}+\sqrt{h_r})$$
d) $$3.56(\sqrt{h_t}-\sqrt{h_r})$$

Explanation: LOS is thedistance covered by a direct space wave from transmitting to receiving antenna.Expression for the LOS distance is $$d = 4.12(\sqrt{h_t}+\sqrt{h_r})$$ in km.
Expression for the Radio horizon distance is $$d =3.56(\sqrt{h_t}+\sqrt{h_r})$$ in km.

5. Expression for radio horizon in km is ____
a) $$4.12(\sqrt{h_t}+\sqrt{h_r})$$
b) $$4.12(\sqrt{h_t}-\sqrt{h_r})$$
c) $$3.56(\sqrt{h_t}+\sqrt{h_r})$$
d) $$3.56(\sqrt{h_t}-\sqrt{h_r})$$

Explanation: Radio horizon is the point to which a space wave can reach maximum. Expression for radio horizon in km is $$d = 3.56(\sqrt{h_t}+\sqrt{h_r})$$
Expression for the LOS distance is $$d = 4.12(\sqrt{h_t}+\sqrt{h_r})$$ in km.

6. The value of k at which LOS equals to the radio horizon is ___
a) 1
b) 0
c) 3/4
d) -3/4

Explanation: Distance between transmitter and receiver is $$d=d_t+d_r=\sqrt{2r_e h_t}+\sqrt{2r_e h_r}$$
And re=k*6370km, k is the effective radius factor.
Expression for radio horizon in km is $$d = 3.56(\sqrt{h_t}+\sqrt{h_r}),$$ LOS depends on k also so d = $$4.12(\sqrt{h_t}+\sqrt{h_r}).$$ At k=1 both will be equal.

7. If the heights of transmitting and receiving antenna are equal then LOS distance is ___ in km.
a) 8.24√h
b) 4.82√h
c) 4.12√h
d) 2.06√h

Explanation: Given heights of transmitting and receiving antenna are equal ht = hr = h
Expression for the LOS distance is $$d = 4.12(\sqrt{h_t}+\sqrt{h_r})$$ in km.
⇨ D=4.12 (2√h) = 8.24√h.

8. Radio horizon is less than LOS distance.
a) True
b) False

Explanation: Expression for radio horizon in km is $$d = 3.56(\sqrt{h_t}+\sqrt{h_r}),$$ Expression for the LOS distance is $$d = 4.12(\sqrt{h_t}+\sqrt{h_r})$$ in km. Under same height conditions, radio horizon is less than LOS. But at effective radius factor k=1, both will be equal.

9. The radio horizon can be equal to the LOS distance if same height antennas are used.
a) True
b) False

Explanation: The radio horizon and LOS become equal when k=1. LOS depends on the height of the transmitting and receiving antennas and effective earth’s radius factor k. Standard value of k is 4/3.

10. What is the value of the effective radius factor k of earth if the radius of curvature and the earth radius equals?
a) 1
b) 0
c) Infinity
d) 4/3

Explanation: Effective radius factor k in terms of radius of curvature rc and radius of earth re is
$$k=\frac{1}{1-\frac{r_e}{r_c}}=\frac{1}{0}=∞.$$

Sanfoundry Global Education & Learning Series – Antennas.

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