Deep Dive: G7C09
The correct answer is B: 90 degrees. The phase difference between the I and Q RF signals that software-defined radio (SDR) equipment uses for modulation and demodulation is 90 degrees. I (In-phase) and Q (Quadrature) signals are 90° apart, allowing complete signal representation. For amateur radio operators, this is fundamental SDR operation. Understanding this helps when using SDR equipment.
Why Other Answers Are Wrong
Option A (Zero): Incorrect. Zero degrees would mean I and Q are in phase - they need to be 90° apart for quadrature operation. Zero degrees doesn't work. Option C (180 degrees): Incorrect. 180 degrees would mean I and Q are opposite phase - they need to be 90° apart for quadrature operation. 180 degrees doesn't work. Option D (45 degrees): Incorrect. 45 degrees is too small - I and Q need to be 90° apart for quadrature operation. 45 degrees doesn't work.
Exam Tip
I and Q phase difference = 90 degrees. Think 'I' and 'Q' = 'I'n-phase and 'Q'uadrature = '9'0 degrees apart. I and Q signals are 90° apart, allowing complete signal representation. Not zero, not 180°, not 45° - just 90°.
Memory Aid
I and Q phase difference = 90 degrees. Think 'I' and 'Q' = '9'0 degrees apart. I and Q signals are 90° apart, allowing complete signal representation. Fundamental SDR operation requirement.
Real-World Example
SDR equipment uses I (In-phase) and Q (Quadrature) signals for modulation and demodulation. The I and Q signals are 90 degrees apart in phase. This quadrature relationship allows the SDR to represent any signal (amplitude and phase) using just I and Q. 90 degrees is the required phase difference.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G7C
Reference: 2023-2027 Question Pool · G7 - Practical Circuits
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G7C topic.