Deep Dive: E4D10
The correct answer is C: A pair of 40 dBm input signals will theoretically generate a third-order intermodulation product that has the same output amplitude as either of the input signals. What does a third-order intercept level of 40 dBm mean with respect to receiver performance is that a pair of 40 dBm input signals will theoretically generate a third-order intermodulation product that has the same output amplitude as either of the input signals. Third-order intercept is where IMD product equals input signal level. For amateur radio operators, this is important for receiver performance. Understanding this helps when evaluating receivers.
Why Other Answers Are Wrong
Option A: Incorrect. Signals less than 40 dBm not generating audible IMD isn't the meaning - third-order intercept is where IMD equals input level. Less than 40 dBm isn't the meaning. Option B: Incorrect. Receiver tolerating signals up to 40 dB above noise floor isn't the meaning - third-order intercept is where IMD equals input level. 40 dB above noise floor isn't the meaning. Option D: Incorrect. Pair of 1 mW signals producing IMD 40 dB stronger isn't the meaning - third-order intercept is where IMD equals input level. 1 mW with 40 dB stronger isn't the meaning.
Exam Tip
Third-order intercept 40 dBm = pair of 40 dBm input signals generates third-order IMD product with same amplitude as input signals. Think 'T'hird-'O'rder 'I'ntercept = 'T'heoretical 'O'utput 'I'ntersection (IMD = input). Third-order intercept is where IMD product equals input signal level. Not less than 40 dBm, not 40 dB above noise, not 1 mW with 40 dB - just 40 dBm where IMD equals input.
Memory Aid
Third-order intercept 40 dBm = pair of 40 dBm input signals generates third-order IMD product with same amplitude as input signals. Think 'T'hird-'O'rder 'I'ntercept = 'I'MD equals input. Third-order intercept is where IMD product equals input signal level. Important for receiver performance.
Real-World Example
A third-order intercept level of 40 dBm: It means that a pair of 40 dBm input signals will theoretically generate a third-order intermodulation product that has the same output amplitude as either of the input signals. This is the intercept point - where IMD product equals input level. This is what it means - 40 dBm where IMD equals input.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E4D
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 E4D topic.