Question

What is the minimum length of antenna required to transmit a radio signal of frequency 20 MHz ?

• A. 5.0 m
• B. 7.5 m
• C. 2.0 m
• D. 3.75 m

Answer 1

Answer: (D)

3.75 m

Given, the frequency of radio signal
$v=20MHz$
$=20\times {10}^{6}Hz$
The wavelength of the antenna is
$\lambda =\frac{c}{v}$
$\lambda =\frac{3\times {10}^8}{20\times {10}^6}$
or $\lambda =15m$
$\therefore$ For efficient radiation and reception, the height of transmitting and receiving antennas should be comparable to a quater wavelength of the frequency used.
$\because$ The minimum length of antenna
$=\frac{\lambda }{4}$
$=\frac{15}{4}=3.75m$