Subelement B: MF-HF-DSC-SITOR (NBDP) Equip. & Operations— Topic :
Question 18B2
Element 9 (GMDSS Maintainer)Which of the following conditions indicate the proper operation of a 250 Watt MF/HF transmitter in the F1B FEC mode?
Explanation
F1B FEC (Forward Error Correction) is a type of FSK (Frequency Shift Keying) digital mode. FSK is a *constant envelope* modulation scheme, meaning the amplitude of the radio frequency (RF) carrier remains constant, while its frequency shifts to encode data (mark and space tones).
For a constant envelope mode like F1B, the RF power output from the transmitter should be constant throughout the transmission, assuming proper amplifier operation. Therefore, a power meter should indicate a steady output level. Operating between 225 and 250 watts for a 250-watt transmitter indicates proper, full-power operation.
Option B is incorrect because FSK transmits a continuous carrier, shifting its frequency, rather than turning the power on and off. Option C is incorrect as an "S" meter measures *received* signal strength, not *transmitted* power, and its readings are typically in S-units, not watts. Option D describes a varying envelope mode (like AM or SSB), where power fluctuates with modulation, which is not characteristic of FSK.
Related Questions
17B6 Which would indicate proper operation of a SSB transmitter rated at 60 Watt PEP output in J3E mode?18B1 Which of the following conditions indicate the proper operation of a 150 Watt MF/HF transmitter in the F1B ARQ mode?18B3 Which of the following conditions could cause very low RF output in a MF/HF transmitter operating in the F1B FEC mode?18B4 which of the following troubleshooting methods is not valid for finding the fault in a MF/HF transmitter operating in the F1B FEC mode?18B5 Which of the following conditions could cause zero RF output in a MF/HF transmitter operating in the F1B FEC mode?