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.
The push for faster
and expanded cellular
services is driven by
the increased use of
streaming video from
Netflix, YouTube, and
others.
Technology and Regulation to
the Rescue
W
Spectrum Shortage Threatens
the Future of Wireless