Wireless Connectivity 101. What Is It?

Introduction

Some may say that this is an obscure post for an audio and video web site. Well, for better or worse wireless communication will eventually supplant most of our cabling, that includes many of those HT cables that you joyfully plug up to make things “talk” to each other. More importantly you will read in the second part of this look at wireless the impact that 5G Wireless is going to have on all of your lives.

So what do the above three pieces of equipment all have in common? They have no wires attached to them, not even power cords. They each communicate by sending and receiving their information via Electromagnetic (EM) waves. This invisible wave is more often referred to as a Radio Frequency (RF) wave and it carries the information to and from and in-between the associated devices. So lets take a 10,000 foot highly simplified view of what RF is and how it carries this information.

A Low Tech Introduction to Wireless.

What is Wireless? In its most basic form it is the communication of information between two points without the use of any physical, light or sound connection. With the increasing popularity of the Internet of Things (IoT) and many household and other devices becoming wireless, it is becoming very much part of today’s society.

The ubiqitous HDMI cable rose out of the need to simplify device connectivity for home users as device connectivity became more and more complex with many video and audio interconnects. Not to mention the desire of film companies to prevent illegal copying of both video and audio. As time, technology and data capacity moved on the desire and need to use cables at all is falling out of favor due to their potential unsightly nature and often problems in running them from point A to point B.

So we now have wireless communication. This is not a new phenomenon. Wireless communication has been with us since Marconi created the first wireless communication on 13th May 1897.

There are many ways of sending information from point A to point B using wireless but they all use the same basic principles. The required information is carried on/used to modify (modulate) a radio frequency (RF) carrier. So first lets understand what RF is then we can review several of the more common/popular modulation techniques that are used to carry the information, be it analog or digital.

The RF carrier.

To talk about RF, we first need to have some understanding of electromagnetic radiation (EMR). These RF carrier waves are generated when a charged particle is accelerated through space, such as being emitted by a transmitting antenna. It creates two oscillating fields that occur perpendicular to each other, an electric field, and a magnetic field. These oscillating fields are called an Electromagnetic (EM) wave, and can be visualised as shown in the image below.

The Electromagnetic Wave

The radiating antenna is connected to an RF power amplifier and converts the electrical energy fed to it into the magnetic and electrical fields similar to how a speakers voice coil converts electrical audio energy from an audio power amplifier into a magnetic field.

The frequency of this RF carrier can be anything shown in the table below. However, each band of frequencies exhibit very specific propagation (transmission) use properties depending upon their application.

As the transmitters RF power energizes the transmitting antenna the current flowing in it creates a magnetic (B) and electrical (E) field around the antenna that radiates out at the speed of light.

Image Credit: Wikipedia. Electromagnetic wave propagating in free space

A simplified transmit/receive signal path

These fields vary in magnitude according to how much power is fed into the antenna and at the frequency selected for the transmission. When this radiating field strikes an object or purpose designed receiving antenna, as shown below, they generate very small voltages in it.

Image Credit: Wikipedia. Electric field generating a voltage in a dipole antenna

In order to receive the RF carrier we need to be able to select its specific frequency at the receiving site. This is the job of the RF tuner which may be fixed to receive a specific frequency or be able to be tuned (like a radio or TV) to select one of many carrier frequencies.

A simplified radio wave receivers block diagram

Once the desired carrier frequency is selected by the RF tuner, a detector circuit demodulates the carrier and extracts the required signal or data.

So now we know what carries the information from point A to point B, a magnetic/electrical field. However, there is a quantity called polarization that effects the direction the transmitting and receiving antennas are physically mounted and/or how they are constructed. An antennas polarization is defined by the angle the EM waves electrical field makes to the surface of the earth. This shall not be reviewed in detail here other than that there are two basics types of polarization:

1. Linear – the electric field remains in the vertical or horizontal planes relative to the earths surface.
   1. Vertical
   2. Horizontal
2. Circular – the electric field continually rotates either clockwise or counterclockwise.
   1. Left hand
   2. Right hand

These types of polarization determine the design of the antenna and whether it is positioned in the vertical or horizontal planes or plane agnostic. The type of polarization used can impact the transmission distance and application of the radiated signal.

Horizontal and vertical polarization

Circular Polarization

So how does this RF carrier signal carry the required information? The technique is known as modulation, of which there are many methods. We shall very briefly review several of the easier and more popular techniques.

Modulation

So what is modulation? It is an electronic technique that allows the analog or digital signal/data that is to be carried by the EM wave to control some parameter of the EM RF sine wave; I.E. its amplitude or frequency for example. These changes to the RF carrier are then detected at the receiver and converted back into the modulating signal.

Common types of modulation include:

• Amplitude Modulation (AM) – Commercial radio and military VLF communications. The required information changes the amplitude of the carrier.
• Frequency Modulation (FM) – Commercial radio, military and public services. The required information changes the frequency of the carrier.
• Phase Modulation (PM) – Military and public services. The required information changes the phase of the carrier; this is analogous to FM above.
• Eight Vestibular Side Band (8VSB) – ATSC1 HD TV OTA Transmission. The digital data is used to set the carrier to one of eight different levels.
• Orthogonal Frequency Division Multiplex (OFDM) – ATSC3 4K(UHD) OTA TV transmission. The digital data is carried on multiple sub-carrier frequencies that are very close in frequency to that of the selected carrier frequency. The modulation method by which the data is carried on the individual sub-carriers varies by application.
• Gaussian Frequency Shift Keying (GFSK) – Blu-Tooth. Computer and other office/home device communications. This is a modified version of frequency shift keying (FSK) that produces discrete changes to the carriers frequency.
• Differential Quadrature Phase-shift keying (DQPSK) and (8-DPSK) – Blu -Tooth. Computer and other office/home device communications. The digital data changes the phase of the carrier signal either relative to the original carrier phase or the phase of the preceding change. A maximum of 8 different phases can be used.

Examples of AM and FM Carrier Modulation

There are numerous other types of modulation techniques and variations available depending upon the use and environment that the transmitted signal is to be put to.

In the above examples the required information that is to be carried by the RF carrier may be analog or digital. However, specific types of modulation technique are generally only suited to either analog or digital signals. Examples would include:

1. Analog Signal Modulation
   1. AM
   2. FM
   3. PM
2. Digital Data Modulation
   1. 8VSB
   2. OFDM
   3. GFSK
   4. PSK

The transmitters modulator or exciter is the electronic circuit that is used to appropriately control the required carriers parameters in order to obtain the modulation technique required.

A simplified RF Transmitter

All RF transmitters and receivers follow the above basic principles. However, their specific implementation varies very considerably with the type of technology and powers required.

So there we have it. An invisible system that transfers information and data from one point to another. However, it is NOT without its problems and dangers. There is no free meal!

1. RF energy is fundamentally dangerous to humans (I am not an alarmist). I know as I worked with it for a large part of my life. (Take a look at some of the Smart meter and Cell phone information. I refused a Smart Meter installation on my house.)
2. RF energy goes everywhere and in many cases to places you do not want it to go.
3. RF energy is cumlative on the receiving body irrespective of what its frequency is.
4. RF energy can be very temperamental and its propagation is not only frequency dependent but also weather and physical obstruction dependent.
5. RF energy is used by the military for crowd control by “mildly” burning people.
6. The long term cummlative health effects of close proximity RF energy, particularly very high frequency RF energy, are still under investigation and are not fully understood.

In the second post in this wireless series we shall take a brief look at 5G Wireless. Its here now and is going to change a lot of the ways in which we now do things and the way, and what, we will be able to do in the future.

Want to know more about real cables, see here.

Still using HDMI cables then take a peak here.

See here for my post on 5G Wireless.