KB6NU's Ham Radio Blog
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2015 General Class Study Guide: G6A: resistors; capacitors; inductors;
rectifiers; solid state diodes and transistors; vacuum tubes; batteries
Posted: 16 Jan 2015 12:34 PM PST
http://feedproxy.google.com/~r/kb6nu...m_medium=email
The question pool committee did something kind of odd here. They combined
sections G6A and G6B from the old question pool into a single section,
eliminating many questions. Im not exactly sure how I feel about thatDan
There are a number of practical considerations you must make when using
electronic components in circuits. For example, the resistance of a
resistor will change depending on the resistors temperature coefficient if
the temperature is increased. (G6A16)
One type of resistor that’s commonly used in electronic is the wire-wound
resistor. Its main advantage is that its value can be set very precisely.
You probably don’t want to use wire-wound resistors in RF circuits, though.
A reason not to use wire-wound resistors in an RF circuit is that the
resistors inductance could make circuit performance unpredictable. (G6A17)
It’s also important to choose capacitors wisely. For example, comparatively
low cost is the primary advantage of ceramic capacitors. (G6A14) A
disadvantage, though, is that they may have a high temperature coefficient.
High capacitance for given volume is an advantage of an electrolytic
capacitor. (G6A15) For this reason, electrolytic capacitors are often used
in power-supply circuits to filter the rectified AC.
Electrolytic capacitors are polarized, meaning that they have both positive
and negative leads. That being the case, you must be careful not to connect
voltages across them that will make the positive lead more negative than
the negative leads. All of these choices are correct when considering why
the polarity of applied voltages is important for polarized capacitors
(G6A13):
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
A popular choice for inductors is the ferrite core inductor. All of these
choices are correct when talking about the advantages of using a ferrite
core with a toroidal inductor (G6A18):
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
Placing two inductors closely together may cause unwanted mutual
inductance, and it is important to minimize the mutual inductance between
two inductors to reduce unwanted coupling between circuits. (G6A11) The
winding axes of two solenoid inductors should be placed at right angles to
each other to minimize their mutual inductance. (G6A10)
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. The approximate junction threshold voltage of a germanium diode is
0.3 volts (G6A03). The approximate junction threshold voltage of a silicon
diode is 0.7 volts. (G6A05)
A type of diode often used in RF circuits is the Schottky diode. Lower
capacitance is an advantage of using a Schottky diode in an RF switching
circuit as compared to a standard silicon diode. (G6A06) The lower
capacitance allows it to switch faster than other types of diodes.
There are two main types of transistors, bipolar transistors and field
effect transistors (FETs). A field effect transistor is the solid state
device most like a vacuum tube in its general operating characteristics.
(G6A11) One type of FET is the Metal Oxide Semiconductor FET, or MOSFET. In
a MOSFET, the gate is separated from the channel with a thin insulating
layer. (G6A09)
Transistors are often used in amateur radio circuits as amplifiers and
switches. When used in an amplifier or as a power supply pass transistor,
the cases of some large power transistors must be insulated from ground to
avoid shorting the collector or drain voltage to ground. (G6A08) When used
as a switch in a logic circuit, the stable operating points for a bipolar
transistor are its saturation and cut-off regions. (G6B07)
Some amateur radio equipment, most notably linear amplifiers, still uses
vacuum tubes. The simplest vacuum tube is the triode, which has three
elements: the cathode, the control grid, and the plate. The control grid is
the element of a triode vacuum tube is used to regulate the flow of
electrons between cathode and plate. (G6A10)
A pentode is a tube with five elements, one of which is called the screen
grid. The primary purpose of a screen grid in a vacuum tube is to reduce
grid-to-plate capacitance. (G6B12)
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. High discharge current is an advantage of the low internal
resistance of Nickel Cadmium batteries. (G6A02)
Carbon-zinc batteries, on the other hand, are not rechargeable. It is never
acceptable to recharge a carbon-zinc primary cell. (G6A04)
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. 10.5 volts is the minimum allowable discharge voltage for maximum life
of a standard 12 volt lead acid battery. (G6A01)
The post 2015 General Class Study Guide: G6A: resistors; capacitors;
inductors; rectifiers; solid state diodes and transistors; vacuum tubes;
batteries appeared first on KB6NUs Ham Radio Blog.