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.
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