Advanced Qualification · A-005 Transmitters, modulation and processing · A-005-001-005
Why must a very stable reference oscillator be used as part of a phase-locked loop (PLL) frequency synthesizer?
- A Any phase variations in the reference oscillator signal will produce phase noise in the synthesizer output
- B Any phase variations in the reference oscillator signal will produce harmonic distortion in the modulating signal
- C Any amplitude variations in the reference oscillator signal will prevent the loop from changing frequency
- D Any amplitude variations in the reference oscillator signal will prevent the loop from locking to the desired signal
Correct answer: A — Any phase variations in the reference oscillator signal will produce phase noise in the synthesizer output. From the official ISED question bank, verified word for word.
Why
A phase-locked loop acts like a strict follower that copies the timing of its reference oscillator to create the final frequency. The full explanation — and one for every question — is in Pro.
Practise this section
Transmitters, modulation and processing: AM, FM, SSB, keying, speech processing, and the numbers behind occupied bandwidth.