Nuts and Volts - December 2016

12 December 2016

OPEN COMMUNICATION n BY LOU FRENZEL W5LEF

What all these things have in common is the need for space in the airwaves. All wireless services use spectrum, and more users and higher data rates mean one thing: more bandwidth and spectrum. The problem is that there is only so much spectrum to be had. Once we use it up, there is no more. So, that’s the issue today. There is a growing spectrum shortage and its effect will be felt by the wireless providers and the rest of us, as well. What can we do about it?

Spectrum 101

The term “spectrum” refers to the wide range of electromagnetic (EM) space that is taken up by radio waves. It is free space in which all wireless signals travel. Radio waves are a combination of an electric field and a magnetic field that travel together at right angles to one another. Their distinguishing characteristics are frequency and wavelength.

λ = 300/fMHz For instance, a 100 MHz FM radio station has a signal wavelength of 300/100 = 3 meters. The higher the frequency, the shorter the wavelength.

The radio spectrum extends 30

kHz to 300 GHz. It’s divided into segments as shown in Table 1.

As for terminology, any signal over 1 GHz is said to be a microwave signal. Signals in the 30 to 300 GHz range are called millimeter waves. The TeraHertz spectrum above 300 GHz is essentially unused as there are so few actual electronic components that can work at these frequencies. Most transistors run out of gain at about 200 GHz. So, THF is basically a no-man’s land.

Beyond 300 GHz is what is known as the optical spectrum. Yes, light is a kind of EM wave. At the lower end is infrared (IR); still used in wireless remote controls and heat sensing applications. Right beyond that is the visible spectrum — red at the low end and violet at the upper end. A little higher in frequency is ultraviolet (uV). Beyond uV are the far-out cosmic and gamma rays.

The most widely used (thereby, the most crowded) spectrum segments are the VHF and UHF bands from 30 MHz to 3 GHz. These areas of the spectrum contain all the mobile radio, cellular, and short-range services like Wi-Fi and Bluetooth. The spectrum between about 300 MHz and 6 GHz is generally known as the “sweet spot.” This prime spectrum is popular as it offers a great balance between range or distance of transmission and reasonable (meaning short) antenna length.

It is important to know and keep in mind that radio waves obey the rules of physics that say that the higher the frequency, the

ireless continues to be the fastest growing segment of electronics. Its growth is driven by cellular data, Wi-Fi, and other short-range technologies.

The Internet of Things (IoT) and the related machine-to-machine (M2M) movements are also creating massive growth opportunities for wireless devices.