Deep Dive: E4B04
The correct answer is A: S11. Which S parameter represents input port return loss or reflection coefficient (equivalent to VSWR) is S11. S11 is the input reflection coefficient. For amateur radio operators, this is important for RF measurements. Understanding this helps when using network analyzers.
Why Other Answers Are Wrong
Option B (S12): Incorrect. S12 is reverse transmission, not input reflection - S11 is input reflection. S12 is reverse. Option C (S21): Incorrect. S21 is forward gain, not input reflection - S11 is input reflection. S21 is forward gain. Option D (S22): Incorrect. S22 is output reflection, not input reflection - S11 is input reflection. S22 is output reflection.
Exam Tip
S parameter for input reflection = S11. Think 'S'11 = 'S'ignal 'R'eflected at port '1' (input). S11 is the input reflection coefficient (return loss/VSWR). Not S12 (reverse), not S21 (forward gain), not S22 (output) - just S11.
Memory Aid
S parameter for input reflection = S11. Think 'S'11 = 'I'nput 'R'eflection. S11 is the input reflection coefficient (return loss/VSWR). Important for RF measurements.
Real-World Example
S parameters: S11 represents input port return loss or reflection coefficient (equivalent to VSWR). S11 measures how much signal is reflected at the input port. This is the parameter - S11 is input reflection.
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.