Subelement B: MF-HF-DSC-SITOR (NBDP) Equip. & Operations— Topic :
Question 14B4
Element 9 (GMDSS Maintainer)The phase locked loop circuit in an MF/HF receiver appears to be faulty. What is the most likely cause?
Explanation
A Phase Locked Loop (PLL) is a feedback control system that generates a stable output frequency by constantly comparing it to a reference. The Voltage Controlled Oscillator (VCO) is the core component within the PLL that *generates* this output frequency. Its oscillation frequency is directly controlled by a voltage from the loop filter, which in turn reflects the phase difference detected. If the VCO is inoperative, it cannot produce any oscillations, fundamentally breaking the PLL's ability to generate or lock onto a frequency.
The AGC circuit controls receiver gain, the Beat Frequency Oscillator (BFO) is used for SSB/CW demodulation, and an IF filter shapes the intermediate frequency bandwidth. These components are external to or peripheral to the PLL's primary function of frequency generation and control; their failure would not directly cause the PLL itself to be inoperative.
Related Questions
14B2 All signals sound normal on an MF/HF receiver except one that has a very high pitched voice barely readable. What is the most likely cause?14B3 You are able to hear signals in the voice/SSB mode but not in the SITOR (NBDP) mode. What is the most likely cause?14B5 You are able to hear signals in the SITOR (NBDP) mode but not in the voice/SSB mode. What is the most likely cause?14B6 The AGC function of an MF/HF receiver is inoperative. What is the most likely cause?15B1 The MF/HF receiver fails to suppress the AF output in the absence of a sufficiently strong input signal. What is the most likely cause?