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March 16, 2019 - August 10, 2021
Using small signal to control or amplify larger signals is called gain.
There are two common types of transistors: bipolar junction transistors (BJT) and field-effect transistors (FET).
RF power transistors are used as the primary gain-producing component in RF power amplifiers.
An integrated circuit (IC or chip) is made of many components connected together as a useful circuit and packaged as a single component.
Fuses are rated by the maximum current they can carry without blowing. They interrupt current overloads by melting a short length of metal.
When the metal melts or “blows,” the current path is broken and power is removed from circuits supplied by the fuse.
Switches and relays control current through a circuit by connecting and disconnecting paths for current to follow.
A switch is operated manually while a relay is a switch controlled by an electromagnet.
Indicators and displays are important components for radio equipment. An indicator is either ON or OFF, such as a power indicator or a label that appears when you are transmitting. A meter provides information as a value in the form of numbers or on a numeric scale.
Resistors are designated with an R, capacitors with a C, inductors with an L, diodes with a D, transistors with a Q and so forth.
schematic does not illustrate the actual physical layout of a circuit. (A pictorial diagram is used for that purpose.) It only shows how the components are connected electrically. The lines drawn from component to component, such as between R1 and Q1, represent those electrical connections. Each line does not necessarily correspond to a physical wire — it just indicates that an electrical connection exists between whatever is at each end of the line.
An oscillator produces a steady signal at one frequency. [T7A05] Oscillators are used in both receivers and transmitters to determine the operating frequency.
The process of combining data or voice signals with an RF signal is modulation. A circuit that performs the modulation function is therefore called a modulator.
A mixer is closely related to a modulator. Mixers combine two RF signals and shift one of them to a third frequency.
Vegetation can also absorb VHF and UHF radio waves. This can result in greater range in the winter.
This type of propagation is called knife-edge diffraction.
Concentrating an antenna’s radiated signals in a specific direction is called gain.
Antenna gain increases signal strength in a specified direction when compared to a reference antenna.
The ratio of the maximum value to minimum value of the interference pattern is called the standing wave ratio or SWR.
Because SWR is determined by the amounts of forward and reflected power, SWR in an antenna system is also a measure of the how well the antenna (or load) and feed line impedances are matched.
When there is no reflected power there is no interference pattern and the SWR is 1:1. This condition is called a perfect match.
SWR greater than 1:1 is called an impedance mismatch or just mismatch.
Low SWR indicates efficient transfer of power from the feed line because less power is reflected by the antenna. That means there is less loss from reflected power in the feed line traveling back and forth between the antenna and transmitter.
Most amateur transmitting equipment is designed to work at full power with an SWR of 2:1 or lower. SWR greater than 2:1 may cause the transmitter’s protection circuits to reduce power automatically to avoid damage to the output transistors.
