Stereo Frequency Multiplexing Quiz

Test your knowledge of stereo frequency multiplexing concepts. Select the best answer for each question.

1. What is the primary purpose of the 19 kHz pilot tone in stereo FM multiplexing?

2. In stereo FM broadcasting, the DSB-SC modulated subcarrier carries which signal?

3. What is the frequency of the subcarrier used in stereo FM multiplexing?

4. Why is DSB-SC (Double Sideband Suppressed Carrier) modulation used for the difference signal?

5. What is the function of the matrix network in a stereo FM receiver?

6. How is the 38 kHz subcarrier generated in a stereo FM receiver?

7. What is the purpose of the SCA (Subsidiary Communications Authorization) channel in FM multiplexing?

8. What is the typical frequency range allocated for the SCA channel?

9. Why is the pilot tone transmitted at exactly half the subcarrier frequency?

10. What is the main advantage of using frequency multiplexing for stereo FM transmission?

Quiz Results

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1. Correct answer: a) To provide a reference for the stereo decoder

The 19 kHz pilot tone serves as a reference signal that allows the receiver to synchronously demodulate the DSB-SC difference signal. It's exactly half the frequency of the 38 kHz subcarrier.

2. Correct answer: b) The difference signal (L-R)

The DSB-SC modulated subcarrier carries the difference signal (L-R), while the baseband contains the sum signal (L+R) for mono compatibility.

3. Correct answer: c) 38 kHz

The subcarrier frequency is 38 kHz, which is twice the pilot tone frequency (19 kHz). This allows receivers to regenerate the subcarrier by doubling the pilot frequency.

4. Correct answer: c) To maintain compatibility with mono receivers

DSB-SC modulation suppresses the carrier, preventing interference with the baseband (L+R) signal. This allows mono receivers to ignore the stereo information and only process the (L+R) signal.

5. Correct answer: b) To separate L and R signals from (L+R) and (L-R)

The matrix network performs the mathematical operations: Left = (L+R) + (L-R) and Right = (L+R) - (L-R) to recover the original left and right audio channels.

6. Correct answer: b) Using a frequency doubler on the 19 kHz pilot

The receiver extracts the 19 kHz pilot tone, then doubles its frequency to generate the 38 kHz subcarrier needed for synchronous demodulation of the DSB-SC signal.

7. Correct answer: a) To transmit additional audio programs

The SCA channel is used to transmit background music, weather information, or other specialized programming to subscribers, typically using narrowband FM.

8. Correct answer: d) 67-92 kHz

The SCA channel typically occupies frequencies from 67 kHz to 92 kHz, well above the stereo information to minimize interference.

9. Correct answer: d) All of the above

Transmitting the pilot at half the subcarrier frequency simplifies receiver design, minimizes interference, and allows easy regeneration of the subcarrier through frequency doubling.

10. Correct answer: b) It maintains compatibility with mono receivers

The key advantage of frequency multiplexing in stereo FM is that mono receivers can still receive the (L+R) baseband signal without any special decoding, ensuring backward compatibility.