easyMultiple Choice
220-1201 Electromagnetic Interference (EMI) Practice Question
A user complains that their wired connection drops randomly for a few seconds then reconnects. The technician suspects electromagnetic interference (EMI) from nearby power cables. Which tool can best confirm the presence of excessive EMI on the network cable?
⚠ Common exam trap
A common mistake is to think a cable tester can confirm EMI, but standard cable testers do not measure external interference. The spectrum analyzer is the correct tool for detecting EMI on network cables.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Spectrum analyzer
A spectrum analyzer is the correct tool because it can detect and measure electromagnetic interference (EMI) by analyzing the frequency spectrum of signals radiated from the cable. This allows the technician to identify excessive EMI from nearby power cables. A standard cable tester checks for continuity, wire mapping, and basic crosstalk but does not directly measure external EMI. A multimeter measures electrical properties like voltage and resistance, not interference. A loopback plug is used to test network ports by sending data back to the device; it does not detect interference.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Multimeter
Why it's wrong here
A multimeter measures voltage, current, and continuity on copper cabling; it cannot detect radiated electromagnetic interference. A cable tester or spectrum analyser identifies EMI. A multimeter would be the right tool for verifying pinouts or checking for a shorted or broken conductor.
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Cable tester
Why it's wrong here
A cable tester verifies physical continuity, pinout, and wiring faults like shorts or opens, but it cannot measure electromagnetic field strength or induced noise on the cable. It is tempting because intermittent drops often suggest a physical-layer fault, and a cable tester is the standard tool for diagnosing broken conductors or miswiring. However, the scenario specifically requires quantifying EMI, which demands a time-domain reflectometer (TDR) or a spectrum analyser to detect signal interference from nearby power cables.
- ✗
Loopback plug
Why it's wrong here
A loopback plug tests a single port's transmit and receive circuitry by echoing signals; it cannot detect radiated EMI along a cable run. It is tempting because it is a common cabling diagnostic, and would be correct for confirming whether a network interface itself is functioning rather than measuring interference.
- ✓
Spectrum analyzer
Why this is correct
A spectrum analyser measures signal amplitude across frequencies, exposing EMI noise from power cables coupling onto the cable. This confirms interference as the cause of the random link drops, unlike a cable tester, which only verifies continuity and wiring.
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Device Driver Installation and Updates
Key term
Cable tester
A cable tester is a device used to verify that network or electrical cables are wired correctly and can carry signals without interruption.
Key term
Loopback plug
A loopback plug is a small device used to test network ports by sending a signal out and immediately receiving it back, verifying that the port is working without needing another device.
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Written by Johnson Ajibi, MSc IT Security
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