Difference between high level modulation and low level modulation.

HIGH LEVEL MODULATION:
parameter:
1. power level: modulation takes place at high modulation level.
2. types of amplifier: highly efficient class c amplifiers are used.
3. efficiency: very high.
4.devices used: vacuum tubes or transistor for medium power applications.
5. design of AF power amplifier: complex due to very high power involved.
6.applications: high power broadcast transmitters.

LOW LEVEL MODULATION:
parameter:
1. power level: modulation takes place at low power level.
2. types of amplifier: linear amplifiers are used after modulation
3. efficiency: lower than high level modulators.
4. devices used: transistors, JFET,OP-AMPs.
5. design of AF amplifier: easy as it is to be done at low power.
6.applications: sometimes used in tv transmitters(IF modulation).

Difference between wideband frequency modulation and narrowband frequency modulation.

WIDEBAND FM:
Parameters :
1. modulation index : Greater than 1
2. maximum deviation: 75 kHz
3. range of modulating frequency: 30 Hz to 15 kHz
4. maximum modulation index: 5 to 2500
5. bandwidth : large,about 15 times higher than BW of narrowband FM
6. applications : entertainment broadcasting
7. pre-emphasis and de-emphasis : is needed.

NARROWBAND FM:
parameters :
1.modulation index: less than or slightly greater than 1
2. maximum deviation: 5kHz
3. range of modulating frequency : 30 Hz to 3 kHz
4. maximum modulation index : slightly greater than 1
5. bandwidth : small.approximately same as that of AM
6. applications: FM mobile communication like police wireless,ambulance etc
7. pre-emphasis and de-emphasis : is needed.

What is the frequency of rotor emf?

When the motor is stationary,rotor conductors are being cut by  rotating flux at synchronous speed.therefore,the frequency of rotor current(or emf)is the same of supply frequency.but when the rotor starts revolving,the rate at which the rotor conductors are being cut by the rotating flux depends upon the relative speed between the rotor and the stator revolving magnetic field , called the slip speedthe frequency of the rotor current (or emf) induced by the relative motion between rotor conductors and the stator revolving magnetic field is given by the equation: