RF Tutorial, Radio Frequency

RF tutorial by TONEX focuses on introducing the fundamental and general concepts of RF and RF security to help you gain some insights. This tutorial is perfect for you if you want to have an overall review of all the aspects of Radio Frequency without going deep into details. This brief article is to guide you towards what you need to learn and to help you discover which parts you need to concentrate based on your needs and interests. It’s goal is to offer a basic comprehension of RF technology, as well act as a fast reference for the individuals who know the subject but may be interested in freshen up on that one special concept that they never fully got.

Brief Background of RF

There is a long and valued background that leads to our current, modern knowledge about radio technology. The very initial studies of what we today name the RF spectrum originated from the first experiments in optics, electricity, and magnetism. Plato, Euclid, Ptolemy, and many others, finally leading to Newton in the late 17th Century, investigated the response of light as far back as the old Greece. From the prehistoric turboelectric materials and chemical batteries, Coulomb, Volta, and Gauss ultimately developed different concepts of electricity. Similarly, lodestones from ancient China invented early philosophies for magnetism from Kuo and Gilbert, finally driving the research of Ampere and again, Gauss.

Prior to the beginning of the 19th Century, electricity and magnetism were considered as separate forces. However, in 1820 Ørsted realized that electric currents utilized a force on magnets, and in 1831 Faraday identified that changes in a magnetic field could induce electrical flows. In 1839, extended experiments in electricity helped Faraday to demonstrate that voltaic electricity (chemical battery), static electricity (triboelectric charge), and magnetically induced currents were all evidence of the same fact. In 1864, Maxwell combined these findings in his paper, “A Dynamical Theory of the Electromagnetic Field”.

RF Modern Theories

Gauss’s Law expresses the electric charge to its electric field. The variance of the electric field changes with the charge density.

Gauss’s Law for Magnetism describes that magnetic monopoles are not really present. The separation of the magnetic field is zero or there is no net magnetic flux getting in or exiting a volume boundaries.

Faraday’s Law of Induction and the Maxwell-Faraday equation express that a varying magnetic field induces an electric field. The bend of the electric field varies with the change in magnetic flux density.

Ampere’s Circuital Law, modified by Maxwell to cover the moves of current connects the magnetic field to a current in a wire. The bend of the magnetic flux density varies with the current density and the change in the electric field.

Definition of Radio

A radio system comprises of both an electromagnetic wave and a planned endpoint for that message. The source radio is considered as the transmitter, while the destination radio is considered the receiver. There are times when only the receiver is necessary, such as in radio astronomy. Likewise, home lighting can demonstrate an example of an optical transmitter. A digital camera would be an example of an optical receiver. Rarely we utilize light to transmit and receive data, such as the old-fashioned Aldis lamps employed by the navies of the world, or the modern-day high-speed fiber optic communication applying diode lasers to transmit and provide photodiodes for the receivers.

What is Transmitter?

A transmitter (TX) is usually a direct device including an oscillating electrical circuit, a technique of altering that oscillation to include information (modulation), an amplifier to enhance the power of that modulated oscillation, and an antenna that converts the electrical signals produced by the transmitter circuitry into an electromagnetic wave.

What is Receiver?

While a transmitter demonstrates a simple design, a receiver (RX) seems to be more complex. The primary receivers are identified simply as an antenna and a load. You can see some leftovers of that simplicity when studying basic RF power transmission in early days. Though, the utmost defeat of the notion of a simple receiver concentrated on two issues of sensitivity and selectivity.

What is Transceiver?

Integrating the power of both of these systems into one functional component was the ultimate result of these early innovators. By coupling the transmitter to a receiver in one system, designers could allocate operation between identical blocks. Parts such as the antenna, reference oscillator, and numerous digital items serve a much more solid product in today’s RF ICs. All of such mixtures in a transceiver design add up to better, denser functionality than the basic parts.

Now Let Us Define RF

RF signals are a type of electromagnetic wave, like visible light, which construct a share of the electromagnetic (EM) spectrum. The EM spectrum includes all types of light, which varies from audible frequencies such as the ubiquitous 60Hz, through the standard radio bands, which encompasses AM Radio, FM Radio, TV channels, and other RF bands. The spectrum revives through infrared, visible, and ultra-violet light, to higher forms of EM energy like X-rays, Gama-rays, and cosmic rays.

What we consider as the Radio or RF spectrum would be in the range of the low-frequency waves that we could hear, if the EM waves were converted into air pressure waves (20Hz to 20kHz), and the high-frequency EM waves that generate infrared and visible light (1mm to 750nm for IR and 750nm to 390nm for visible (or about 400THz to 770THz)).

The RF spectrum is more distributed into traditional bands, which are typically categorized by their frequency range and broken throughout decades. For instance, the 300MHz to 3GHz range is named the UHF band. In the UHF, SHF, and EHF bands, organization such as the IEEE and NATO manage to divide the bands up into smaller classes.

In the United States, the Federal Communications Commission (FCC) is the responsible organization that directs the RF spectrum share and allowable applications. The role of the FCC and its foreign counterparts is required to give central organization of this partial resource and to implement a structure that provides compatible functionality of the several radio frequency systems. In the absence of these regulating agencies, everybody could broadcast regardless of frequency, power, bandwidth, or duty cycle. This could lead to monopolizing the airwaves and would most likely interfere with important shapes of command, control, and communication.

RF Overview

Amplitude and Power

V – Voltage: In RF systems, the voltage of a signal is usually referred to a 50Ω load.

P – Power: In an RF system, power is usually referred to a 50Ω load.

P = VI = V²/R

dB – Decibels: This is a unitless ratio measure (similar to %) applied in RF systems when discussing power. The ratio “dBm” is more common in RF applications where the “m” refers to using 1mW as the referenced point.

dBm = dBW+ 30dB

L(dB) = 10. Log₁₀(V_out/V_in)

Field Strength

V/m – Volts per meter: A measure applied in electrical field strength. It is often more common to see values with higher resolution units such as mV/m or μV/m.

Frequency Domain

Carrier: referring to the RF frequency or the fundamental, and sometimes \as the f primary, or first harmonic. The carrier is the main EM wave frequency applied in a radio link. This is the sinusoidal signal, moderated to carry or tolerate the transmitted data throughout free space for eventual reception and decoding. If applied in a dual-frequency modulated system, the carrier may be the average between the two mark and space frequencies.

Band: a part of the RF spectrum that is usually applied as a frequency demarcation by government entities and kept by those authorities for particular uses.

Bandwidth: a window of frequencies throughout the RF spectrum. This is used to define a part of the spectrum or range of frequencies associated with a specific signal or broadcast transmission. Bandwidth can also consider as a property of particular radio components such as an amplifier or a filter. Filter bandwidths deal with the 3dB frequencies. The basic formula for a bandwidth is:

BW= f_H-f_L

Where BW is the bandwidth

f_H is the highest frequency in the system

fL is the lowest frequency in the system

Channel: referring to a thin layer of a frequency band that can include a moderated carrier. Such a band may be distributed into several channels, all of which applied for the similar objective and are usually described by a center frequency and a bandwidth.

Harmonic frequency, aka harmonics: sinusoidal content at integer multiples of the carrier frequency. Harmonics are considered by their integer such as 2f, 3f, 5f, or second, third, fifth, etc. Harmonic frequencies are the outcome of non-idealities of a waveform. While a mathematically pure sine wave does not accomplish to harmonic frequencies, any periodic waveform will demonstrate some harmonic content. The scale of the harmonic content can reform a periodic signal.

RF Instruments