hardMultiple Choice
220-1201 Practice Question: A technician is troubleshooting a DSL connection…
A technician is troubleshooting a DSL connection that keeps disconnecting. The modem shows the DSL light blinking. After checking the phone line, they find a filter is missing on a nearby phone handset. How does this cause the issue?
⚠ Common exam trap
Many candidates confuse a missing filter with a power or short-circuit issue, overlooking the fundamental principle that DSL and POTS share the same wire pair but require frequency separation to avoid interference.
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
✓
The missing filter allows voice frequencies to interfere with DSL frequencies
DSL operates at frequencies above the voice band (typically 25 kHz to 1.1 MHz for ADSL), while analog phone handsets use the 0–4 kHz range. A missing filter (microfilter) allows the phone handset's impedance changes and noise from voice-band signals to reflect onto the DSL line, causing crosstalk and signal-to-noise ratio degradation. This interference triggers frequent retrains and disconnections, visible as a blinking DSL light.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The phone handset draws too much power from the line
Why it's wrong here
A missing filter does not increase power draw; handsets draw negligible line current regardless. Without the low-pass filter, the handset injects high-frequency noise onto the line, corrupting the DSL signal and causing the modem to lose sync. Power draw would be relevant only for line-powered analogue phones.
- ✓
The missing filter allows voice frequencies to interfere with DSL frequencies
Why this is correct
DSL and voice share the same copper pair but occupy different frequency bands. Without a microfilter, the handset's low-frequency voice signals and impedance changes leak onto the line, disrupting the higher-frequency DSL band and causing the modem's DSL light to blink as it loses sync.
- ✗
The filter is needed to amplify the DSL signal
Why it's wrong here
Filters are passive low-pass devices that block DSL frequencies from reaching analogue phones; they do not amplify anything. The missing filter lets handset noise interfere with the DSL band, breaking synchronisation. Amplification would describe a repeater or signal booster, not a microfilter.
- ✗
The phone handset creates a short circuit without the filter
Why it's wrong here
A missing filter does not create a short circuit; the handset still operates normally for voice calls. The filter's role is to isolate high-frequency DSL traffic from the analogue handset, preventing impedance changes and noise from disrupting the DSL signal. Short circuits would trip protection, not merely blink the DSL light.
Go deeper
Related to this question
About these practice questions
Courseiva writes every 220-1201 question from scratch — 871 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.