Question E8A07:
What determines the PEP-to-average power ratio of an unprocessed single-sideband phone signal?  

Choices:  
A: The frequency of the modulating signal  
B: Speech characteristics  
C: The degree of carrier suppression  
D: Amplifier gain    

Correct Answer is  B: Speech characteristics  

Correct answer: B — Speech characteristics

Why B is correct:
- The PEP-to-average power ratio (also called crest factor) of an unprocessed SSB voice signal depends on how “peaky” the spoken audio is—your syllables, consonants, and dynamics.
- Peaks in the audio produce peaks in the RF envelope, so the ratio is set by the statistical nature of speech.

Key relationships:
- Peak Envelope Power:
  $$PEP = \max\left(\frac{V_{\text{env}}^2}{2R}\right)$$
- Average power:
  $$P_{\text{avg}} = \frac{1}{T}\int_0^T \frac{V_{\text{env}}^2}{2R}\,dt$$
- Crest factor (ratio and dB):
  $$CF = \frac{PEP}{P_{\text{avg}}}, \quad CF_{dB} = 10\log_{10}\!\left(\frac{PEP}{P_{\text{avg}}}\right)$$
- Rules of thumb:
  - Unprocessed speech: $CF_{dB} \approx 8$–12 dB (often around 10 dB).
  - With speech processing/compression: $CF_{dB}$ reduced (easier average power).
  - Two-tone test (equal tones): $CF_{dB} \approx 3$ dB ($PEP \approx 2 \times P_{\text{avg}}$).

Why the other choices are incorrect:
- A: Frequency of the modulating signal
  - The crest factor depends on amplitude variations, not the specific audio frequency, as long as it’s within the SSB passband.
- C: The degree of carrier suppression
  - SSB suppresses the carrier; residual carrier would add a steady component, but for an unprocessed SSB voice signal the dominant factor is the speech waveform, not carrier suppression.
- D: Amplifier gain
  - In a linear system, gain scales both peak and average equally, so the ratio $PEP/P_{\text{avg}}$ is unchanged. Only processing (compression/limiting) or distortion would alter the ratio.