A
revolution is occurring in amateur radio that
opens up new opportunities for low-cost
worldwide conversations. With only an entry-level
amateur license, a budget handheld radio, and a
Raspberry Pi with a radio hat, you can now talk to
hams all over the world. This article will introduce
amateur digital voice (DV) technologies so that
you can get started in this exciting aspect of the
ham radio hobby.
Traditional analog voice tech has been losing
ground to digital voice technologies for years.
Voice over Internet Protocol (VoIP), audio and
video streaming, cellphones — they all perform
analog-to-digital conversion of audio signals.
As digital data, it can be packetized, routed, and
manipulated in ways that aren’t feasible with
analog signals. Amateur radio, also known as
ham radio, started experimenting with digital
modes like Radio Teletype (RTTY) as far back as
1946, though arguably Continuous Wave (CW), aka
Morse Code, is the original digital mode and has
been with us since the inception of amateur radio
in 1912. But as the internet gained prominence,
so too did ham radio’s interest in advanced digital
modes including digitized audio.
Like many aspects of the amateur service,
many options exist for amateur digital voice.
The three most common are: Digital Mobile
Radio (DMR), Digital Smart Technology (aka
D-Star), and Yaesu’s System Fusion (aka
Fusion or YSF) (Figure
A
). All three share a
high level architecture and are interoperable to
varying degrees. While each mode has strong
proponents, I’ll generally focus on DMR for
this introduction.
PROPAGATING OVER THE INTERNET
Worldwide analog radio works by sendingout
(propagating) oscillating waves of electromagnetic
radiation that bounce off the ionosphere to
cover long distances. These radio waves have
to compete with artificial and natural sources
of noise to be intelligible when received. Digital
voice avoids this noise by using the internet to
send digitized audio around the world. Radios
with special codec chips encode and decode the
digital signals, but typically are only used to make
short-distance transmissions to a radio-enabled
access point, either a local repeater or a personal
hotspot (Figure
B
). This assures the quality
of the audio when it makes a local hop from a
repeater or hotspot to the receiving radio.
The majority of DV activity occurs on VHF/
UHF bands (2m and 70cm), with local, line-
of-sight propagation. However, some HF
radios (160m–10m) have DV capabilities and
can propagate signals much farther via the
ionosphere. We’ll stick to the more common VHF/
UHF DV solutions for this introduction.
The minimal things needed to get started in
DV are; an entry-level Technician Class amateur
radio license, a handheld transceiver (HT) with
a codec chip, and a local repeater or personal
DV hotspots.
Radio frequency
(e.g. 439.55MHz)
Handheld
DMR Radio
Data
Mic
MMDVM
hat
RasPi
Router/
modem
ISP
Vocoder
(e.g. AMBE+2)
Frame
assembly
Transmit
Hotspot
INTERNET
Wi-Fi (or Ethernet)
DIGITAL MOBILE RADIO
COMMON COMPONENTS
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A
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