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Basic Electronics Definitions

Basic Electronics - Diodes And PN Junctions

A diode is a two-terminal device (thermionic diodes may also have one or two ancillary terminals for a heater).

Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property. The varicap diode is used as an electrically adjustable capacitor.

The unidirectionality most diodes exhibit is sometimes generically called the rectifying property. The most common function of a diode is to allow an electric current in one direction (called the forward biased condition) and to block the current in the opposite direction (the reverse biased condition). Thus, the diode can be thought of as an electronic version of a check valve.

Real diodes do not display such a perfect on-off directionality but have a more complex non-linear electrical characteristic, which depends on the particular type of diode technology. Diodes also have many other functions in which they are not designed to operate in this on-off manner.

Early diodes included “cat’s whisker” crystals and vacuum tube devices (also called thermionic valves). Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.

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Basic Electronics - Kirchhoff's Law

Just as Ohm's Law is a basic building block for electronic circuits, Kirchhoff's law have to be understood properly to understand the complexities of electrical or electronic circuits.

Kirchhoff's circuit laws are two equalities that deal with the conservation of charge and energy in electrical circuits, and were first described in 1845 by Gustav Kirchhoff. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws.

The two primary rules set by Kirchoff are as follows

  • Kirchhoff's current law (KCL)
  • Kirchhoff's voltage law (KVL)
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Basic Electronics - Ohm's Law

Probably the most important law in electronics is Ohm's Law.

Ohms Law:  The voltage across a resistor equals the resistance of the resistor times the current flowing through it (V = R* I).

Ohm's law applies to electrical circuits; and in other words can be stated as "The current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them" 

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Basic Electronics - Voltage Current and Resistance

Voltage, Current and Resistance

Electric currents flow along wires to transmit energy for domestic and industrial purposes. To understand many electrical phenomena, it is only necessary to learn a few simple rules of circuit analysis and these will be the underlying theme of this section on VU2.IN.

  • Voltage - also termed as potential difference. Represented by letter V
  • Current - Amount of electron flow. Represented by letter I
  • Resistance - The fundamental force that opposes flow of current. Represented by letter R
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Radio Frequency Amplifier : RF Amplifier

Radio Frequency Amplifier

An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter. It is usually optimized to have high efficiency, high output Power(P1dB) compression, good return loss on the input and output, good gain, and optimum heat dissipation.

The basic applications of the RF amplifiers include driving to another high power source, driving a transmitting antenna, microwave heating, and exciting resonant cavity structures. Among these applications, driving transmitter antennas is most well known. The transmitter–receivers are used not only for voice and data communication but also for weather sensing (in the form of a RADAR). Microwave or RF heating is an industrial application which is also benefiting our homes in the form of microwave ovens. Exciting cavity resonators is quite a research lab and industrial application of an RF source. Particle accelerators utilize RF sources extensively.

Amplifiers are available in a large number of form factors ranging from miniscule ICs to the largest high-power transmitter amplifiers. In the following discussion the focus will be on solid state power amplifiers used at microwave frequencies, particularly in test and measurement applications.

Microwave power amplifiers may be used for applications ranging from testing passive elements, such as antennas, to active devices such as limiter diodes or MMIC based power amplifiers.

Furthermore, other applications include testing requirements where a relatively large amount of RF power is necessary for overcoming system losses to a radiating element, such as may be found at a compact range, or where there is a system requirement to radiate a device-under-test (DUT) with an intense electromagnetic field, as may be found in EMI/EMC applications.

As varied as the system requirements may be, the specific requirements of a given amplifier can also vary considerably. Nevertheless, there are common requirements for nearly all amplifiers, including frequency range, gain/gain flatness, power output, linearity, noise figure/noise power, matching, and stability. Often there are design trade-offs required to optimize any one parameter over another, and performance compromises are usually necessary for an amplifier that may be used in a general purpose testing application.

In other words a radio frequency amplifier is a tuned amplifier that amplifies the high-frequency signals commonly used in radio communications. The frequency at which maximum gain occurs in a radio-frequency (rf) amplifier is made variable by changing either the capacitance or the inductance of the tuned circuit. A typical application is the amplification of the signal received from an antenna before it is mixed with a local oscillator signal in the first detector of a radio receiver. The amplifier that follows the first detector is a special type of rf amplifier known as an intermediate-frequency (i-f) amplifier. See also Amplifier; Intermediate-frequency amplifier.

An rf amplifier is distinguished by its ability to tune over the desired range of input frequencies. The shunt capacitance, which adversely affects the gain of a resistance-capacitance coupled amplifier, becomes a part of the tuning capacitance in the rf amplifier, thus permitting high gain at radio frequencies. The power gain of an rf amplifier is always limited at high radio frequencies, however.

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Newsflash

WARD - World Amateur Radio Day April 18th

April 18th is the 108th day of the year (109th in leap years). This day marks the founding day of International Amateur Radio Union (IARU), thus the official birthday since 1925 has been celebrated as World Amateur Radio Day.  

By all means World Amateur Radio Day remains an individual thing, there is absolutely no compulsion or fancy events to commemorate the day organized on a global or national scale. This being a special day though each HAM is encouraged to promote the hobby, increase awareness, get on air and spread the good word.

Amateur Radio has come a long way over the years. The first spark-gap devices served as transmitters for first three decades of the radio (1887 - 1916) and today we have moved on to digital signals, SDRs integration with computers has shown how HAM Radio remains in the forefront of evolving technology.