BDS RF Fundamentals and Signal Theory 1 — Questions and Answers
Question 1: What is the standard downstream frequency range used in DOCSIS 3.1 systems?
- 5–42 MHz
- 54–1002 MHz
- 108–1218 MHz (Correct answer)
- 1 GHz–3 GHz
Correct answer: 108–1218 MHz
DOCSIS 3.1 expands the downstream spectrum to 108–1218 MHz to support higher capacity using OFDM channels.
Question 2: What unit measures the ratio of signal power to noise power in a cable system?
- dBmV
- dBc
- SNR (dB) (Correct answer)
- BER
Correct answer: SNR (dB)
Signal-to-Noise Ratio (SNR), expressed in decibels (dB), measures how much stronger the desired signal is compared to background noise.
Question 3: Which modulation scheme carries the most bits per symbol in HFC downstream signals?
- 64-QAM
- 256-QAM
- 1024-QAM (Correct answer)
- QPSK
Correct answer: 1024-QAM
1024-QAM encodes 10 bits per symbol, making it the highest-density modulation used in modern DOCSIS 3.1 deployments.
Question 4: What does a -6 dBmV reading indicate compared to 0 dBmV?
- Signal is twice as strong
- Signal is half the power
- Signal is one-quarter the power (Correct answer)
- Signal is six times stronger
Correct answer: Signal is one-quarter the power
A 6 dB drop represents a factor-of-4 reduction in power because dB is a logarithmic scale where 6 dB ≈ 4× power ratio.
Question 5: What phenomenon causes signal levels to vary across the frequency spectrum due to different attenuation rates at different frequencies?
- Ingress
- Tilt (Correct answer)
- Reflection
- Distortion
Correct answer: Tilt
Tilt refers to the frequency-dependent slope in signal levels where higher frequencies experience more attenuation than lower frequencies through coaxial cable.
Question 6: What is the typical upstream frequency range in a DOCSIS 3.0 cable plant?
- 5–42 MHz (Correct answer)
- 54–750 MHz
- 750–1000 MHz
- 1002–1218 MHz
Correct answer: 5–42 MHz
DOCSIS 3.0 uses 5–42 MHz for upstream transmission, a range shared with legacy return-path signals.
BDS RF Fundamentals and Signal Theory 1
What is the standard downstream frequency range used in DOCSIS 3.1 systems?