The maximum distance between the transmitting and receiving antennas is $D$. If the heights of both transmitting and receiving antennas are doubled, then the maximum distance between the two antennas is

For an amplitude modulated wave, the maximum and minimum amplitudes are found to be 10 V and 2 V respectively. Then, the modulation index is

The process of the loss of strength of a signal while propagating through a medium is

A message signal of peak voltage 12 V is used to amplitude modulate a carrier signal of frequency 1.2 MHz . The amplitude of the side bands is