BDS Network Testing and Measurement 2

Question 1

What is a BER test and what does it verify?

Accepted Answer

Bit Error Rate test — verifies the number of bits received in error per total bits transmitted to assess digital link quality

Answer

A BER (Bit Error Rate) test measures the ratio of errored bits to total transmitted bits, providing a statistical measure of digital channel quality; pre-FEC and post-FEC BER together reveal the severity of impairments.

Question 2

What does a constellation diagram reveal about a QAM signal?

Accepted Answer

The distribution of received symbol points relative to ideal positions, revealing noise, phase noise, amplitude compression, and other impairments

Answer

A QAM constellation diagram plots the in-phase (I) and quadrature (Q) components of each received symbol; tight clusters near ideal points indicate a clean signal, while spread, rotated, or compressed clusters reveal specific impairment types.

Question 3

When using a signal level meter, what does a high pre-FEC BER but a clean post-FEC BER indicate?

Accepted Answer

The FEC is successfully correcting errors, but the signal has impairments that will eventually overwhelm FEC if conditions worsen

Answer

High pre-FEC BER with clean post-FEC BER means FEC is correcting errors successfully, but the margin is being consumed — if impairments increase slightly, FEC will be overwhelmed and post-FEC errors will appear.

Question 4

What is return loss and how is it measured at a cable connector?

Accepted Answer

The ratio of reflected power to incident power at a connector or device port, measured in dB — higher return loss (more negative dB) means less reflection

Answer

Return loss measures how much of the incident signal is reflected back from a connector or device; a high return loss value (e.g., –20 dB) indicates minimal reflection, while low return loss (e.g., –6 dB) indicates poor impedance matching.

Question 5

What tool is most effective for identifying narrowband ingress in the upstream spectrum?

Accepted Answer

Spectrum analyzer connected to an upstream test point at the node or amplifier

Answer

A spectrum analyzer connected to an upstream test point displays the full return path spectrum, making narrowband ingress signals (such as ham radio or shortwave interference) immediately visible as unexpected carriers within the upstream band.

BDS - Broadband Distribution Specialist Practice Test

BDS - Broadband Distribution Specialist Practice Test

BDS Network Testing and Measurement 2