Upconverting is the process of converting the intermediate frequencies to a block of higher frequency signals. The upconverter, for example, uses a Local Oscillators and can be found in Radio telecommunications systems and computers. For highest frequency stability, and best phase noise, a phase locked local oscillators is typically used. A DRO (Dielectric Resonant Oscillator) can be used for a fixed frequency Local oscillator.
Phase Locked Loop (PLL)
A PLL is an electronic circuit that consists of a voltage controlled oscillator (VCO)with a phase detector a reference oscillator (usually a crystal oscillator) and an active loop amplifier/designed loop bandwidth.A phase locked loop is a control system that generates an output signal with a phase related to that of the higher stability reference signal
How Does A PLL Work?
A PLL has the few major components to perform the following functions:
– The VCO (voltage controlled oscillator) that generates an RF signal – The phase detector that compares the phase of the reference signal with the generated signal – The phase detector continually adjusts the oscillator to match the phase and frequency
Uses of a PLL
– To demodulate a modulated RF signal – To recover a signal from a high noise environment. – To generate a stable frequency at multiples of a reference frequency – To generate precisely timed clock pulses in digital logic circuits
Block Upconverter (BUC)
Transmission of satellite signals usually takes place with the help of Block Upconverter (BUC). It converts a band of frequencies from a lower IF (intermediate frequency) to higher frequency. Modern BUCs convert from L band to C, KU band and Kaband, for example.
Low Noise Block Downconverter LNBs (receive) and BUCs (Transmit) typically use phase locked loop local oscillators which usually require a (10 or 100MHzetc) frequency reference to maintain a stable transmit and receive frequency.