Subelement B: MF-HF-DSC-SITOR (NBDP) Equip. & Operations— Topic :
Question 14B2
Element 9 (GMDSS Maintainer)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?
Explanation
When receiving a Single Sideband (SSB) signal, your receiver's Beat Frequency Oscillator (BFO) must be set to precisely the correct frequency relative to the incoming signal's suppressed carrier to properly demodulate the voice. If the transmitting station's frequency is off (either too high or too low) relative to where your receiver is tuned, the BFO will beat against a shifted signal, resulting in audio that is either too high-pitched, too low-pitched, or garbled and barely readable.
Since "all other signals sound normal," it indicates the problem lies with that specific signal's transmission, not your receiver's general functionality. A defective receiver synthesizer, VCO, or BFO circuit would likely affect *all* SSB signals, not just one. Therefore, the most likely cause is the abnormal signal's transmitter operating off its intended frequency.
Related Questions
13B6 How does a noise blanker circuit work in a HF receiver?14B1 The voice is garbled and unreadable on MF/HF SSB channels. 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?14B4 The phase locked loop circuit in an MF/HF receiver appears to be faulty. 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?