numerical on modulation index

1. Numericals

4. A modulated wave on CRO has maximum span of
5V and a minimum of 1 V. Find the modulation
index.
• Vmax=5v
• Vmin=1v
m=vmax-vmin/vmax+vmin
=5-1/5+1
=4/6
=0.67

5. A sinusoidal carrier voltage of frequency 1500 kHz is amplitude
modulated by a sinusoidal voltage of frequency 20kHz resulting in
maximum and minimum modulated carrier amplitudes of 120V and 80
V resp. Find:
• Freq of lower and upper sideband.
• Modulation index and amplitude of each sideband.
Amplitude of each sideband=mEC/2
=0.2*120/2=12

6. For an AM transmitter with an unmodulated carrier power Pc=100W which is
modulated simultaneously by three modulating signals with m1= 0.2 , m2=0.4,
m3=.5. Find
1. Effective modulation index.
2. Upper and Lower sideband power
3. Total transmitted power.
Pt= Pc(1+m2/2)
Psb=(Pc.m2/2)/2

7. The output current of 60% modulated AM generator is 1.5A. Find
What will this current if the generator is modulated additionally by another audio wave with
modulation index of 0.7?
What will be the %age power saved if the carrier and one of the sidebands are now suppressed?

8. What is total power when modulation index is
0.75 and carrier power is 500W?

9. What are carrier power and sideband power with
modulation index of 0.25 when transmitter is
capable of 100 W maximum total power?

10. The r.m.s antenna current of the radio transmitter is 5A
when unmodulated, rising to 6A when the carrier
sinusoid ally modulated. Find the modulation index

11. A transmitter with 10kW carrier transmits 11.2kW when
modulated with a single sine wave. Calculate the modulation
index. If the carrier is simultaneously modulated with another
sine wave at 50% modulation. Find the total transmitted
power.

12. A broadcast radio transmitter radiates 10 kW
when a modulation percentage is 60. How much
of this is carrier power?

13. A certain transmitter radiates 9kW with the carrier
unmodulated, and 10.125kW when the carrier is sinusoidally
modulated. Calculate the modulation index, %age of
modulation. If another sine wave corresponding to 40%
modulation is transmitted simultaneously, determine the total
radiated power.

14. • Calculate the percentage power saving when a carrier and one of the
sidebands are suppressed in AM wave modulated to the depth of
1)100% and 2) 50%