FE Electrical & Computer Practice Question Solution included after investigation
CASE E-035 · FE

The AM Signal Whose Envelope Pinched Shut

The carrier was 5 V. The message amplitude was 6 V. The envelope detector stopped reproducing the message cleanly.

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Inspect, commit, prove, fix, and sign off.

Case E-035 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 conventional AM transmitter uses a 5 V carrier amplitude and a 6 V sinusoidal message amplitude. The technician expects the stronger message to improve the received audio, but an envelope detector produces severe distortion. Diagnose the modulation setting, calculate the modulation index, and choose a correction that restores valid envelope detection.

Communications Electrical & Computer Design Verification Root Cause Analysis Safe Correction
E-035
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

The envelope detector produced distortion.

What was assumed

More message amplitude was assumed to be always beneficial.

Corrected model

Check m=Am/Ac and keep m≤1 for conventional AM envelope detection.

QUICK ANSWER

For single-tone conventional AM, the modulation index is m=Am/Ac. With a 6 V message and 5 V carrier, m=1.2, or 120%. Because m>1, the AM envelope is overmodulated and simple envelope detection produces distortion.

ENGINEERING TAKEAWAY

For standard AM with envelope detection, keep 0≤m≤1. The modulation index is m=Am/Ac for a single-tone message.

CASE QUESTIONS

Questions this case should settle.

What is the modulation index for Am=6 V and Ac=5 V?

m=6/5=1.2, or 120%.

When does conventional AM become overmodulated?

When the modulation index exceeds 1.

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?

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What happens after I complete a case?

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