Deep Dive: E4B03
The correct answer is C: S21. Which S parameter is equivalent to forward gain is S21. S21 represents forward transmission (gain) from port 1 to port 2. For amateur radio operators, this is important for RF measurements. Understanding this helps when using network analyzers.
Why Other Answers Are Wrong
Option A (S11): Incorrect. S11 is input reflection, not forward gain - S21 is forward gain. S11 is reflection. Option B (S12): Incorrect. S12 is reverse transmission, not forward gain - S21 is forward gain. S12 is reverse. Option D (S22): Incorrect. S22 is output reflection, not forward gain - S21 is forward gain. S22 is reflection.
Exam Tip
S parameter for forward gain = S21. Think 'S'21 = 'S'ignal from port '2' to port '1' (forward). S21 represents forward transmission (gain) from port 1 to port 2. Not S11 (input reflection), not S12 (reverse), not S22 (output reflection) - just S21.
Memory Aid
S parameter for forward gain = S21. Think 'S'21 = 'F'orward gain. S21 represents forward transmission (gain) from port 1 to port 2. Important for RF measurements.
Real-World Example
S parameters: S21 is equivalent to forward gain. S21 represents forward transmission (gain) from port 1 to port 2. For example, in an amplifier, S21 would be the gain. This is the parameter - S21 is forward gain.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E4B
Reference: 2024-2028 Question Pool · E4 - Amateur Practices
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E4B topic.