Question

Two towers on top of two hills are 40 km apart. The line joining
them passes 50 m above a hill halfway between the towers. What is

the longest wavelength of radio waves, which can be sent between

the towers without appreciable diffraction effects?​

Answer 1

Explanation:

Distance between the towers is 40km.Height of the line joining the hills is d=50m.Thus, the radial spread of the radio waves should not exceed 50 m.Since the hill is located halfway between the towers, Fresnel’s distance can be obtained. =20kmAperture is a=d=50mFresnel’s distance is given by the relation,

=12.5cm

Answer 2

Answer:

Distance between the towers is 40km.

Height of the line joining the hills is d=50m.

Thus, the radial spread of the radio waves should not exceed 50 m.

Since the hill is located halfway between the towers, Fresnel’s distance can be obtained.

Zp =20km

Aperture is a=d=50m

Fresnel’s distance is given by the relation,

Zp =a 2 /λ=2×10 is power 4

λ=a 2 /Zp =12.5cm