Deep Dive: E7E08
The correct answer is C: The two input frequencies along with their sum and difference frequencies. What are the principal frequencies that appear at the output of a mixer are the two input frequencies along with their sum and difference frequencies. Mixers produce sum and difference frequencies. For amateur radio operators, this is important for mixer theory. Understanding this helps when working with mixers.
Why Other Answers Are Wrong
Option A: Incorrect. Two and four times input frequency isn't correct - mixer produces sum and difference frequencies. 2x and 4x isn't correct. Option B: Incorrect. Square root of product of input frequencies isn't correct - mixer produces sum and difference frequencies. Square root isn't correct. Option D: Incorrect. 1.414 and 0.707 times input frequency isn't correct - mixer produces sum and difference frequencies. 1.414/0.707 isn't correct.
Exam Tip
Principal frequencies at mixer output = two input frequencies + sum and difference frequencies. Think 'M'ixer = 'M'ixes frequencies (sum and difference). Mixers produce sum and difference frequencies. Not 2x/4x, not square root, not 1.414/0.707 - just input frequencies + sum and difference.
Memory Aid
Principal frequencies at mixer output = two input frequencies + sum and difference frequencies. Think 'M'ixer = 'S'um and 'D'ifference. Mixers produce sum and difference frequencies. Important for mixer theory.
Real-World Example
The principal frequencies at the output of a mixer: They are the two input frequencies along with their sum and difference frequencies. For example, if inputs are f1 and f2, outputs include f1, f2, f1+f2, and f1-f2. This is what appears - input frequencies + sum and difference.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E7E
Reference: 2024-2028 Question Pool · E7 - Practical Circuits
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E7E topic.