General: Overmodulation

Which of the following is an effect of overmodulation? [G8A08]

A. Insufficient audio
B. Insufficient bandwidth
C. Frequency drift
D. Excessive bandwidth

The answer is D. Excessive bandwidth.  Now, for the purposes of getting this question correct on the exam, I’ll just say this: Just remember the connection between overmodulation and excessive bandwidth.

The real reason this occurs, is technically fairly complex, and rather than try and rewrite and research it on my own, I’ll just point you at this informative piece at stackexchange: http://electronics.stackexchange.com/questions/107128/what-is-overmodulation

They have some animations that clearly show what is going on there, showing the development of the spurious emissions that develop in an AM radio signal when overmodulated.

The above image shows a normally modulated FM signal.  If I locate a decent example or demo of how this also applies in the FM realm, I’ll add to this entry.

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