Deep Dive: E7G12
The correct answer is A: A high-gain, direct-coupled differential amplifier with very high input impedance and very low output impedance. An operational amplifier (op-amp) is a high-gain, direct-coupled differential amplifier with very high input impedance (typically megohms) and very low output impedance (typically a few ohms). Op-amps are integrated circuits designed to amplify the difference between two input voltages. They're 'direct-coupled' meaning they can amplify DC signals as well as AC signals. The very high input impedance means they draw minimal current from the signal source, and the very low output impedance means they can drive loads effectively. Op-amps are fundamental building blocks in analog electronics, used in amplifiers, filters, oscillators, and many other circuits. The characteristics described in option A are the defining features of operational amplifiers.
Why Other Answers Are Wrong
Option B: Incorrect. Op-amps are analog amplifiers, not digital audio amplifiers. Their characteristics are determined by internal design, not just external components. Option C: Incorrect. Op-amps aren't specifically for increasing FM signal output to legal limits. They're general-purpose analog amplifiers used in many applications. Option D: Incorrect. Op-amps aren't specifically RF amplifiers for UHF and microwave. They're typically used at lower frequencies (audio, DC, low RF).
Exam Tip
Op-amp definition = High-gain differential amplifier. Remember: An op-amp is a high-gain, direct-coupled differential amplifier with very high input impedance and very low output impedance.
Memory Aid
**O**p-amp = **O**utstanding **P**erformance: **H**igh **G**ain, **H**igh **I**nput, **L**ow **O**utput (think 'OP = OPHGHILO')
Real-World Example
You're building an audio preamplifier using an op-amp. The op-amp's very high input impedance (10 megohms) means it doesn't load down your microphone, and its very low output impedance (10 ohms) means it can drive your headphones effectively. The high gain (100,000 or more) allows you to amplify weak signals, and the differential inputs let you amplify the difference between two signals.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E7G
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E7G topic.