A spectrum analyser shows a fundamental at 100,text MHz and a spur at 110,text MHz . This 10,text MHz spur is most likely caused by:

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Electronics Engineering QUESTION #11729

Question 1

A spectrum analyser shows a fundamental at $100\,\text{MHz}$ and a spur at $110\,\text{MHz}$. This $10\,\text{MHz}$ spur is most likely caused by:

Harmonic distortion in the power amplifier
Intermodulation or mixing with a $10\,\text{MHz}$ reference clock signal✔️
Cable impedance mismatch creating standing waves
The spectrum analyser's own local oscillator leakage

Correct Answer Explanation

A spur exactly offset by $10\,\text{MHz}$ from the carrier strongly suggests mixing (intermodulation) between the $100\,\text{MHz}$ signal and a $10\,\text{MHz}$ reference, clock, or IF signal present in the system — producing sum ($110\,\text{MHz}$) and difference ($90\,\text{MHz}$) products. Harmonics would appear at $200\,\text{MHz}$, $300\,\text{MHz}$, etc.

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