BDS RF Fundamentals and Signal Theory 2 — Questions and Answers
Question 1: What does the term 'carrier-to-noise ratio' (CNR) describe in a cable system?
- The ratio of digital to analog channels
- The ratio of carrier power to thermal noise floor (Correct answer)
- The number of carriers per node
- The ratio of upstream to downstream bandwidth
Correct answer: The ratio of carrier power to thermal noise floor
CNR measures the power of a specific carrier relative to the thermal noise floor, determining the usable quality of that signal.
Question 2: Which distortion product results from third-order nonlinearity and falls on active carrier frequencies?
- Composite Second Order (CSO)
- Composite Triple Beat (CTB) (Correct answer)
- Cross Modulation
- Hum Modulation
Correct answer: Composite Triple Beat (CTB)
Composite Triple Beat (CTB) is a third-order distortion product that clusters on active channel frequencies and degrades picture quality.
Question 3: What is ingress noise in a cable plant?
- Noise generated by amplifier electronics
- External RF signals leaking into the cable system (Correct answer)
- Signal reflections from impedance mismatches
- Thermal noise from coax conductor resistance
Correct answer: External RF signals leaking into the cable system
Ingress is unwanted external RF energy (such as amateur radio or FM broadcast signals) that leaks into the cable plant through damaged connectors or loose fittings.
Question 4: What is the standard impedance of coaxial cable used in HFC distribution networks?
- 50 ohms
- 75 ohms (Correct answer)
- 100 ohms
- 300 ohms
Correct answer: 75 ohms
HFC cable systems use 75-ohm coaxial cable, which optimizes the balance between power handling and signal loss for broadband distribution.
Question 5: What does MER (Modulation Error Ratio) measure in a digital cable system?
- The number of modulation errors per second
- The quality of a digitally modulated signal compared to an ideal signal (Correct answer)
- The ratio of downstream to upstream modulation order
- The carrier frequency offset from nominal
Correct answer: The quality of a digitally modulated signal compared to an ideal signal
MER measures the ratio of average symbol power to error vector power, serving as a key quality metric for digitally modulated signals like QAM.
Question 6: Which type of passive device splits a signal into multiple equal-output ports while introducing insertion loss?
- Directional coupler
- Splitter (Correct answer)
- Attenuator
- Equalizer
Correct answer: Splitter
A splitter divides the input signal equally among its output ports, with each split adding approximately 3.5 dB of insertion loss for a two-way split.
BDS RF Fundamentals and Signal Theory 2
What does the term 'carrier-to-noise ratio' (CNR) describe in a cable system?