The process of recovering the modulating signal from the modulated carrier wave is called:

The amplitude of $15 \sin (1000 \pi t)$ is modulated by $10 \sin (4 \pi t)$ signal. The amplitude modulated signal contains frequencies of
$1. 500\,Hz$
$2. 2\,Hz$
$3. 250\,Hz$
$4. 498\,Hz$
$5. 502\,Hz$
Choose the correct answer from the options given below:

Radio waves that reach the receiver after being reflected from the ionosphere propagate via .......

For transmission of e.m. wave of audible frequency,these waves are superimposed with waves of

$A$ $TV$ transmission tower antenna is at a height of $20\, m$. Suppose that the receiving antenna is at:
$(i)$ ground level
$(ii)$ a height of $5\, m$.
The increase in antenna range in case $(ii)$ relative to case $(i)$ is $n\%$.
The value of $n$,to the nearest integer,is .....$\%$

In a communication system,a repeater is used to extend the range of transmission. It is a combination of: