As the name indicates, class AB amplifiers operate somewhere between class A and class B. Or perhaps the name is short for "Almost B" -- which would be true as well.

A class A amplifier operates at a full 360 degrees. The purity of amplification is terrific, but the efficiency is not.

Class B amplification uses two "finals", each operating for 180 degrees of the wave -- a great improvement in efficiency. However, with the introduction of bipolar transistors as finals, a problem with class B amplification developed. In a pure class-B configuration, there is a period of time where neither the forward-going nor the negative-going final has a forward-biased base-emitter junction. When this type of amplifier is fed a pure sine wave, there is a "hitch" at the zero crossing caused by neither final being forward-biased. This is called crossover distortion, and is a highly undesirable alteration of a pure sine wave.

The simple and elegant solution to this was to bias the finals so that each one operates slightly more than 180 degrees (but less than 360 degrees) to eliminate the problem of crossover distortion. The result is an amplifier with "Almost Class B" efficiency, but with distortion characteristics close to class A. Or, as it is called, Class AB.

Last edited by orochimaru. Register to edit

Tags: arrl chapter 6 arrl module 6c

Just remember that the key feature of Class D amplifiers is high efficiency.

Each one of the wrong answers misleads you by putting the letter D in the description: differential, drift-mode, and doubling.

Trick: Class D, D is for Digital -> Technology is the answer.

Last edited by phongn. Register to edit

Tags: arrl chapter 6 arrl module 6c

Switching amplifiers generate harmonics due to their rapid switching between on and off states, which creates high-frequency components at multiples of the fundamental signal frequency.

These harmonics are a problem because they can distort the signal, cause interference to other stations, and violate regulatory limits. Basically without a filter to remove harmonics which are generated by the amplifier you'd be transmitting on other frequencies that you don't intend to transmit on.

Last edited by kd7bbc. Register to edit

Tags: none

Setting the bias half-way between saturation and cutoff gives the maximum possible swing in collector voltage without entering either saturation or cut- off.

Last edited by orochimaru. Register to edit

Tags: arrl chapter 6 arrl module 6c

Unwanted oscillations are also called parasitic oscillations. Naturally, a parasitic suppressor suppresses parasitic oscillations.

SWR, power, and phase are all more or less unrelated to oscillation.

Silly Hint: Parasites are unwanted

Last edited by sympathique. Register to edit

Tags: arrl chapter 6 arrl module 6c

A grounded-grid amplifier is a type of RF amplifier commonly used in high-power applications like linear amplifiers for transmitting. In this amplifier, the control grid of the tube is connected directly to the ground, and the input signal is applied to the cathode while the output is taken from the plate (anode).

• Low Input Impedance: Because the input signal is applied to the cathode, which is a low-impedance point, grounded-grid amplifiers naturally have a low input impedance. This low impedance makes them easy to drive with other radio equipment, which is essential for efficient power transfer.

Why the Other Answers are Incorrect:

• High Power Gain: Grounded-grid amplifiers typically have moderate power gain, not high. Most of the gain comes from the ability to handle large power rather than amplifying the signal greatly.

• High Electrostatic Damage Protection: Nothing about this type of amplifier protects against electrostatic damage.

• Low Bandwidth (D): Grounded-grid amplifiers generally have reasonable bandwidth, suitable for many applications, but bandwidth is not specifically low.

Memory Aid: The ground is under your feet so it is low and won't impede your walk.

Last edited by kd7bbc. Register to edit

Tags: arrl chapter 6 arrl module 6b

From Wikipedia: "Class-C amplifiers conduct less than 50% of the input signal and the distortion at the output is high". So, the option that mentions distortion is correct.

Silly hint: Class C - correct answer contains words starting with the next letters in the alphabet; signal distortion and excessive bandwidth. (c, d, &e).

Last edited by jaeger21. Register to edit

Tags: arrl chapter 6 arrl module 6c

Linear amplifiers (such as Class A amps) bias transistors in their linear region. Whenever these transistors are conducting they are never fully on nor off, but have some instantaneous resistance which generates heat.

An ideal switch when closed has 0 ohms of resistance, and when open has infinite resistance. In either case the switch does not generate any heat.

Transistors in switching amplifiers act much like switches--they are either on or off most of the time. Because switched transistors are seldom partially on they don't generate much heat, resulting in low power dissipation compared to transistors operating in their linear region.

Hint: 'linear' descriptor of time, only answer with 'time'

Hint: The only one that doesn’t say amplifier

Last edited by antoszewski. Register to edit

Tags: arrl chapter 6 arrl module 6c

An emitter follower, also known as a common collector amplifier, is a transistor amplifier where:

• Configuration: The output is taken from the emitter terminal, and the input is applied to the base.
• Voltage Gain: It has a voltage gain close to 1, meaning it doesn't amplify the signal in terms of voltage but provides high current gain.
• In-Phase Signals: The input and output signals are in-phase because the emitter voltage closely tracks the base voltage. This results in the output signal (taken from the emitter) having the same phase as the input signal (applied to the base), due to the small voltage drop between the base and emitter in the forward-active region of the transistor.

Last edited by kd7bbc. Register to edit

Tags: none