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or (in some systems like GSM which is still in use), eight signals
per spectrum channel. This really multiplied their subscriber
capacity. Also created around this time was Code Division
Multiple Access (CDMA) which further expanded the capacity of
the cellular network. Today, all cell phones are digital and a wide
range of different technologies are involved.
better fidelity than the AM and FM stations. AM stations sound
more like FM and FM stations sound more like CDs.
Furthermore, the HD signals are more immune to noise and do
not fade as much when you are driving.
Q: Are two-way mobile radios also digital?
A: Some of them are but not all. Many like those used in
fire, police, and public services still use FM. Digital technologies
like P25 and Tetra have been around a while but the different
services have been slow to convert. Military radios are mostly
digital today.
Q: Does the rest of the world have digital radio?
A: Yes, pretty much. Europe has had digital radio for years
with a system called Eureka-147. You will hear it referred to as
Digital Audio Broadcast (DAB). It broadcasts music and other
programs in digital on the VHF bands (not the usual AM low
frequency bands) allotted for that. Canada has a similar system.
Q: What about marine and aircraft radios?
A: Strangely, both are still analog. Marine radios use FM and
aircraft radios use AM. I’m not sure of all the reasons for that,
but I assume that since the ranges are short and the spectrum is
not so crowded, why change? Besides, the technologies are well
proven and the equipment is moderately priced and very
reliable.
Q: What about broadcast radio?
A: Analog AM and FM stations are still around and still the
most widely used. However, most stations have added a digital
capability called HD radio. The station’s programs are digitized
and broadcast in digital format on exactly the same frequency as
the analog signals. The digital signals overlay the analog signals.
Analog radios ignore the digital while an HD radio receiver can
pick up the digital signals. The digital capability also allows most
radio stations to broadcast two or three other programs
simultaneously thanks to the multiplexing capability.
Q: What about TV?
A: As you probably know, TV went all digital last year. All
the analog stations went off the air and switched to digital which
gave us high definition TV. If you still have an old analog set, you
have to use one of those converter boxes that translates the
digital TV signals to analog so your old set can handle them. All
new sets sold today are digital only. Almost everyone loves
digital TV as it has such improved resolution. Over 50% of the
US population today has an HD set with a big LCD or plasma
screen. There is also the mobile TV from FLO TV that you may
have heard about. It was developed to provide digital TV to cell
phones and portable/mobile TVs like those in cars and SUVs.
Q: Tell me more about digital HD radio.
A: Well, it has been around for years but in the past five
years or so most stations have added it. I am not so sure that
most folks actually know about it. You can readily buy an HD
radio for about $100 at Best Buy, RadioShack, or any other
consumer electronics retailer. Many cars come with HD or offer
it as an option. The big deal about HD is that is gives slightly
Q: Is digital TV unique to the US?
A: No, not really. Europe went to digital TV a number of
years ago with its Digital Video Broadcast (DVB) standard. Japan
has their ISDB (Integrated Services Digital Broadcast) system and
South Korea uses their DMB (Digital Media Broadcast) system.
Most of these digital TV standards have mobile versions for
broadcasts to cell phones. The US is working on a mobile
version of its Advanced Television Standards Committee (ATSC)
standard for digital TV in the US. It should be available in the
near future in some cell phones.
Q: Are there any radio services that have not moved to digital?
A: Yes, namely the hobby radio services. CB radio is still AM
and SSB. The family radio service (FRS) is still FM. So is most
ham radio which relies heavily on SSB and FM. Morse coded
CW is a form of digital and that modulation is Amplitude Shift
Keying (ASK) — a form of AM. Hams also use a form of digital
called PSK31. These services lack the spectrum and the FCC
restricts their modulation methods, but the movement is in
the digital direction.
Q: What about shortwave radio?
A: Shortwave (SW) radio is still mostly analog. Virtually
all worldwide stations broadcast in AM. It uses minimum
bandwidth in a crowded spectrum but it is susceptible to
noise as you know if you listen to SW.
■ FIGURE 1. C.Crane’s CC Wi-Fi
digital Internet radio connects
wirelessly by Wi-Fi to your
home router or by a direct
Ethernet cable connection.
Q: Will shortwave ever go digital?
A: Yes, and it is already happening. A digital standard
called Digital Radio Mondiale (DRM) was developed and uses
voice compression along with CODFM modulation. It is used
primarily in Europe. The result is good quality audio that fits
within the assigned narrow ( 20 kHz or less) SW channels. It’s
not wide spread yet, but it seems to be catching on. A
number of radios are available in Europe but there are few
on sale in the US. Some of the new digital software-defined radios have DRM demodulators.
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October 2010
