BDS Signal Distribution and Amplification 2 — Questions and Answers
Question 1: What is the typical input impedance of coaxial cable distribution equipment in a US cable broadband system?
- 50 ohms
- 75 ohms (Correct answer)
- 100 ohms
- 120 ohms
Correct answer: 75 ohms
All cable broadband distribution equipment in the US is designed for a 75-ohm impedance environment, matching the characteristic impedance of the coaxial cable.
Question 2: Which specification describes the maximum allowable level difference between the highest and lowest RF channels at an amplifier output?
- Tilt (Correct answer)
- Slope
- Gain
- Response flatness
Correct answer: Tilt
Tilt refers to the intentional or measured difference in signal level between the lowest and highest frequency channels across the amplifier's passband.
Question 3: A line extender amplifier is typically used in what part of the cable distribution network?
- At the headend to boost headend output
- On the trunk cable between the headend and nodes
- On feeder or distribution cables to extend reach to taps (Correct answer)
- Inside the customer home to boost CPE signals
Correct answer: On feeder or distribution cables to extend reach to taps
Line extender amplifiers are placed on feeder/distribution cables to overcome additional attenuation and serve tap clusters farther from the node or bridger.
Question 4: What is the purpose of an automatic gain control (AGC) circuit in a cable amplifier?
- To set the upstream return path gain
- To maintain a constant output level despite input level variations (Correct answer)
- To equalize the frequency response across the passband
- To reduce intermodulation distortion products
Correct answer: To maintain a constant output level despite input level variations
AGC circuits automatically adjust amplifier gain to compensate for signal level variations caused by temperature changes or upstream disturbances, maintaining a stable output.
Question 5: Which type of splitter divides a cable signal equally between two output ports?
- Directional coupler
- 2-way splitter (Correct answer)
- Diplexer
- Attenuator
Correct answer: 2-way splitter
A 2-way splitter divides the input signal equally, with each output port receiving approximately 3.5 dB less signal than the input (3 dB split loss plus ~0.5 dB insertion loss).
Question 6: What is the minimum acceptable CNR level typically required for acceptable QAM-256 signal quality in a US cable system?
- 20 dB
- 27 dB
- 33 dB (Correct answer)
- 40 dB
Correct answer: 33 dB
QAM-256 modulation requires a minimum CNR of approximately 33 dB to maintain acceptable BER performance in a cable broadband system.
BDS Signal Distribution and Amplification 2
What is the typical input impedance of coaxial cable distribution equipment in a US cable broadband system?