FE Electrical & Computer Practice Question Solution included after investigation
CASE E-036 · FE

The PCM Link That Needed 64 kbps, Not 32

The voice channel bandwidth was 4 kHz. The data link was sized at 32 kbps and immediately overflowed.

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Case E-036 engineering failure visual
HOW THIS WORKS

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Follow the investigation process used in the field — in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A voice signal is band-limited to 4 kHz and encoded using ideal PCM with 8 bits per sample. A link budget allocates 32 kbps by multiplying 4 kHz by 8 bits. The encoder produces twice that data rate. Diagnose the missing sampling factor, calculate the minimum raw PCM bit rate, and determine whether a 50 kbps channel can carry the stream without compression.

Communications Electrical & Computer Design Verification Root Cause Analysis Safe Correction
E-036
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Find the root cause, confirm the fix, and see how this connects to the exam.

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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

A 32 kbps link was allocated for a 64 kbps raw PCM stream.

What was assumed

Analog bandwidth was treated as sampling rate.

Corrected model

Apply Nyquist first, then multiply sampling rate by bits per sample.

QUICK ANSWER

For ideal PCM, sample a band-limited signal at fs≥2B, then multiply by the number of bits per sample. For B=4 kHz and 8 bits/sample, fs=8 kSa/s and the raw bit rate is 64 kbps.

ENGINEERING TAKEAWAY

For ideal baseband PCM, first choose fs≥2B, then compute Rb=fs×n bits/sample. Framing or coding overhead, if present, is additional.

CASE QUESTIONS

Questions this case should settle.

What is the PCM bit rate for 4 kHz bandwidth and 8 bits per sample at Nyquist sampling?

64 kbps.

Is analog bandwidth the same as PCM sampling rate?

No. Ideal Nyquist sampling requires at least twice the highest signal frequency or baseband bandwidth for the stated case.

NEXT FE PRACTICE QUESTION

The Four-Channel FDM Link That Needed 95 kHz

Communications · 5–10 min

Continue Practice →
WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

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Are the cases aligned with engineering exams?

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What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.