What is the RF modulated to?

What is the RF modulated to?

• A. 60 Hz
• B. 85 Hz
• C. 255 Hz
• D. 155 Hz

Answer: (D)

The signal uses a low-frequency subcarrier to carry the data, so the RF carrier is modulated by a fixed subcarrier tone. In this system that subcarrier is 155 Hz. Choosing 155 Hz keeps the modulated spectrum within the receiver’s filter bandwidth and away from common interference like 60 Hz mains noise, while also aligning with the detector’s reference for clean demodulation. A subcarrier at 60 Hz would be plagued by mains hum, and 85 Hz or 255 Hz would require different filter tuning or could overlap with other channels, making reliable demodulation harder. So 155 Hz is the appropriate modulating frequency.

The signal uses a low-frequency subcarrier to carry the data, so the RF carrier is modulated by a fixed subcarrier tone. In this system that subcarrier is 155 Hz. Choosing 155 Hz keeps the modulated spectrum within the receiver’s filter bandwidth and away from common interference like 60 Hz mains noise, while also aligning with the detector’s reference for clean demodulation. A subcarrier at 60 Hz would be plagued by mains hum, and 85 Hz or 255 Hz would require different filter tuning or could overlap with other channels, making reliable demodulation harder. So 155 Hz is the appropriate modulating frequency.