Electronics Theory

Here’s chapter 2 of the updated General Class study guide. I was surprised by some of the questions that they eliminated. For example, they deleted question, “What is a microprocessor?”…….Dan

Resistors; capacitors; inductors; rectifiers; solid state diodes and transistors; vacuum tubes; batteries

There are a number of practical considerations you must make when using electronic components in circuits. Wire-wound resistors, for example, are great in DC circuits because they offer high precision, but because the wire in a wire-wound resistor is actually a coil of wire, they may not be a good choice for RF circuits.

QUESTION: Which of the following is a reason not to use wire-wound resistors in an RF circuit? (G6A06)

ANSWER: The resistor’s inductance could make circuit performance unpredictable

Cost is often also a consideration. Low cost is one reason ceramic capacitors are often used in electronic circuits.

QUESTION: Which of the following is an advantage of ceramic capacitors as compared to other types of capacitors? (G6A14)

ANSWER: Comparatively low cost

One disadvantage of ceramic capacitors is that they cannot be used where a high capacitance is needed, such as in the filter of an AC power supply. For this application, we generally use electrolytic capacitors. Electrolytic capacitors are polarized, meaning that they have both positive and negative leads. That being the case, you must be careful not to connect them so that the voltage on the positive lead is negative with respect to the voltage on the negative lead.

QUESTION: Which of the following is an advantage of an electrolytic capacitor? (G6A04)

ANSWER: High capacitance for a given volume

QUESTION: Why is the polarity of applied voltages important for polarized capacitors? (G6A13)

ANSWER: All of these choices are correct
• Incorrect polarity can cause the capacitor to short-circuit
• Reverse voltages can destroy the dielectric layer of an electrolytic capacitor
• The capacitor could overheat and explode

Both capacitors and inductors are used in RF circuits. A popular choice for inductors is the ferrite core inductor. It consists of a coil of wire wound around a ferrite core.

QUESTION: What is an advantage of using a ferrite core toroidal inductor? (G6A08)

ANSWER: All of these choices are correct
• Large values of inductance may be obtained
• The magnetic properties of the core may be optimized for a specific range of frequencies
• Most of the magnetic field is contained in the core

There are different types of ferrite materials, and how the ferrite material in a ferrite core is made will affect how it performs in an RF circuit.

QUESTION: What determines the performance of a ferrite core at different frequencies? (G6B01)

ANSWER: The composition, or “mix,” of materials used

One application for a ferrite bead or ferrite core is to provide the inductance needed to reduce or eliminate RF currents that may cause RF feedback, which can cause equipment to malfunction.

QUESTION: How does a ferrite bead or core reduce common-mode RF current on the shield of a coaxial cable? (G6B10)

ANSWER: By creating an impedance in the current’s path

Like other components, inductors are not perfect. In addition to the inductance, inductors have a parasitic capacitance that must be taken into account. The frequency at which the parasitic capacitance of the inductor resonates with the ideal inductance of the inductor is called the self-resonant frequency.

QUESTION: What happens when an inductor is operated above its self-resonant frequency? (G6A11)

ANSWER: It becomes capacitive

The diode is one of the most versatile components. They are used to rectify AC voltages, regulate DC voltages, switch RF voltages, and demodulate radio signals. One of the most important diode specifications is the junction threshold voltage. This voltage will be different for different types of diodes. Silicon diodes, which are the most widely-used type of diode, have a higher junction threshold voltage than germanium diodes.

QUESTION: What is the approximate junction threshold voltage of a conventional silicon diode? (G6A05)

ANSWER: 0.7 volts

QUESTION: What is the approximate junction threshold voltage of a germanium diode? (G6A03)

ANSWER: 0.3 volts

Transistors are the real workhorses in modern electronic equipment. They are available in single-transistor packages or in integrated circuits, which may consist of millions of transistors. There are two main types of transistors, bipolar transistors and field effect transistors (FETs).One type of FET is the Metal Oxide Semiconductor FET, or MOSFET. Metal oxide layers in a MOSFET insulate the semiconductor layers from one another.

QUESTION: Which of the following describes the construction of a MOSFET? (G6A09)

ANSWER: The gate is separated from the channel with a thin insulating layer

Transistors are often used in amateur radio circuits as amplifiers and switches. When used as a switch, a small base current controls a larger current flowing through the transistor. This current is either on or off. When off, the transistor is said to be operating in its cutoff region. When on, the transistor is operating in its saturation region.

QUESTION: What are the stable operating points for a bipolar transistor used as a switch in a logic circuit? (G6A07)

ANSWER: Its saturation and cutoff regions

Some amateur radio equipment, most notably linear amplifiers, still use vacuum tubes. The simplest vacuum tube is the triode, which has three elements: the cathode, the control grid, and the plate. The control grid, as the name implies, controls the flow of electrons from the cathode to the plate.

QUESTION: Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate? (G6A10)

ANSWER: Control grid

One disadvantage of a triode is parasitic capacitance between the control grid and the plate. To reduce this capacitances, a tube called a pentode, because it has five total elements, has an element called the screen grid.

QUESTION: What is the primary purpose of a screen grid in a vacuum tube? (G6A12)

ANSWER: To reduce grid-to-plate capacitance

Batteries are often used to power amateur radio equipment, so it’s important to know their characteristics and how to use them. Some batteries can be used only once, while others are rechargeable. Nickel-cadmium batteries, sometimes called “Ni-Cads,” are one type of rechargeable battery. Because they have a low internal resistance, they can supply a high current.

QUESTION: What is an advantage of the low internal resistance of nickel-cadmium batteries? (G6A02)

ANSWER: High discharge current

For applications that require long battery life, 12 volt lead-acid batteries, often car batteries or deep cycle marine batteries, are used. When using these batteries, it’s important to not discharge them all the way.

QUESTION: What is the minimum allowable discharge voltage for maximum life of a standard 12 volt lead-acid battery? (G6A01)

ANSWER: 10.5 volts

Analog and digital integrated circuits (ICs); memory; I/O devices; microwave ICs (MMICs); display devices; connectors

Most amateur radio devices today contain integrated circuits (ICs). On a single piece of silicon, manufacturers can put thousands of transistors, implementing very complex circuit functions. ICs may include analog circuits, digital circuits, or a combination of both. A simple example of an analog integrated circuit is the operational amplifier, or op amp.

QUESTION: What kind of device is an integrated circuit operational amplifier? (G6B06)

ANSWER: Analog

A more sophisticated analog IC is the MMIC, which can operate at frequencies in the microwave range.

QUESTION: What is meant by the term MMIC? (G6B02)

ANSWER: Monolithic Microwave Integrated Circuit

Digital ICs are often described by the technology used to create the transistors. One type, or “family,” of digital IC uses complementary, metal-oxide semiconductor, or CMOS, transistors. CMOS has several advantages over other IC technologies, such as transistor-transistor logic (TTL).

QUESTION: Which of the following is an advantage of CMOS integrated circuits compared to TTL integrated circuits? (G6B03)

ANSWER: Low power consumption

Memories are an important type of digital IC. One type of memory is the read-only memory, or ROM, which is often used to store programs or data that never changes.

QUESTION: What is meant by the term ROM? (G6B04)

ANSWER: Read Only Memory

QUESTION: What is meant when memory is characterized as non-volatile? (G6B05)

ANSWER: The stored information is maintained even if power is removed

Modern transceivers use light-emitting diodes (LEDs) or liquid crystal displays (LCDs) to display operating status, such as frequency. LEDs actually emit light when current flows through them. LCDs on the other hand, do not emit light, but instead become opaque when a voltage is applied across them. Because of that, they may need some sort of light to make them readable.

QUESTION: How is an LED biased when emitting light? (G6B08)

ANSWER: Forward biased

QUESTION: Which of the following is a characteristic of a liquid crystal display? (G6B09)

ANSWER: It utilizes ambient or back lighting

To connect all of the devices we typically have in an amateur radio station, we use many different types of connectors. For audio signals, we typically use phone or RCA phone jacks and plugs.

QUESTION: Which of these connector types is commonly used for audio signals in Amateur Radio stations? (G6B11)

ANSWER: RCA Phono

There are many different types of connectors designed specifically to connect RF signals. These include PL-259s, N connectors, and SMA connectors.

QUESTION: Which of these connector types is commonly used for RF connections at frequencies up to 150 MHz? (G6B12)

ANSWER: PL-259

QUESTION: Which of the following describes a type N connector? (G6B07)

ANSWER: A moisture-resistant RF connector useful to 10 GHz

QUESTION: What is a type SMA connector? (G6B11)

ANSWER: A small threaded connector suitable for signals up to several GHz