The sound produced by a tuning fork is a/an .....

$A$ $..........$ is used in the receiver section to reduce the magnitude of signals.

The electron density of $E, F_1, F_2$ layers of the ionosphere is $2 \times 10^{11} \, m^{-3}$,$5 \times 10^{11} \, m^{-3}$,and $8 \times 10^{11} \, m^{-3}$ respectively. What is the ratio of critical frequencies for the reflection of radio waves?

The height of a transmitting antenna is $h \ m$ and the height of a receiving antenna is $45 \ m$. The distance between them is $40 \ km$. For satisfactory $Line\, of\, Sight$ $(LOS)$ communication between the two antennas,the height of the transmitting antenna $h$ must be ....... $m$. (Radius of the Earth $R = 6400 \ km$)

The loss of strength of a signal while propagating through a medium is known as

$A$ message signal is used to modulate a carrier signal of frequency $5 MHz$ and peak voltage of $40 V$. In the process,two side-bands are produced separated by $40 kHz$. If the modulation index is $0.75$,then the peak voltage and frequency of the message signal,respectively,are: