FM GENERATION Direct Method: when the frequency of carrier is modulated by information signal Indirect Method: when the phase of carrier is modulated by information signal
Generation of FM waves Varactor diode modulator( Direct method) Reactance modulator( Direct method) Crosby FM direct transmitter Armstrong method (Indirect method)
- more capacitance. - less capacitance.
Varactor Diode FM modulator
CIRCUIT DIAGRAM OF VARACTOR DIODE MODULATOR
FET REACTANCE MODULATOR .
Modulating signal Career Frequency modulation Phase modulation
INDIRECT FM GENERATION Integrator
+ =
FREQUENCY UP-CONVERSION With FM and PM modulators, the carrier at the output is generally somewhat lower than the desired frequency of transmission. There are two basic methods of performing frequency up conversion. Heterodyning process Frequency multiplication
HETERODYNE METHOD OF FREQUENCY UP-CONVERSION
MULTIPLICATION METHOD OF UP-CONVERSION
BLOCK DIGRAM OF CROSBY DIRECT FM TRANSMITTER
Block Diagram of FM Receiver