Question

A baseband signal of 3.5 MHz frequency is modulated with a carrier signal of 3.5 GHz frequency using amplitude modulation method. What should be the minimum size of antenna required to transmit the modulated signal?

• A. 42.8 m
• B. 42.8 mm
• C. 21.4 mm
• D. 21.4 m

Answer 1

Answer: (C)

21.4 mm

Answer 2

$ν_c$ = 3.5×109 Hz

∴ λ=$\frac{c}{\nu}$

λ=$\frac{3×10^8}{3.5×10^9}$ = $8.57×10^{−24}$

∴ Size of antenna = $\frac{\lambda}{4}$

= $\frac{8.57×10^{−24}}4$

= $21.4 mm$

The correct option is (C) : 21.4 mm