DIGITAL RADIO FOR VOICE
EVOLUTION OF RADIO COMMUNICATION SYSTEMS
WHY DIGITAL VOICE - LOUD CLAIMS FIRST ☺
• What would you say to nearly noise-free voice quality, clearer transmissions, and no
background interference?
• How would you like to allow multiple groups to use one repeater on the same
frequency at the same time?
• How would you like to reduce the transmission rate of your radio by one-half or more, extending
the battery life longer than ever before?
• How would you like to have your own personal repeater (hotspot) that can connect to any
other repeater across the world?
Trends in Digital Voice, W0AKO
EVOLUTION OF COMMUNICATION MODES
Telephone Telegraph Modem GSM 4G
Analog CW RTTY Packet Digital
Radio Radio Radio
Antenna
RF Amp Mixer Band Pass Filter IF Amp Demodulator AF Amp Audio
Local
Oscillator
Conventional Radio Architecture
Antenna
Analog<>Digital Analog<>Digital
DSP Processor
RF Amp Mixer Band Pass Filter IF Amp Converter Converter Audio
Local
Oscillator RF Frontend
(SDR based) Digital Radio Architecture
DSP FOR DIGITAL RADIO
• Voice Coder for Compression of Voice Signals
• AMBE-2+ by DVSI is used in most DV systems (Patented)
• Codec2 developed by David Rowe VK5DGR used in FreeDV (Opensource Experimental)
• Packetizied Digital Modulation Schemes • Forward Error Correction – soft “decoding”
• 4FSK, GMSK, C4FM • Multiplex Access Schemes – strict timing management
TIME DIVISION MULTIPLEX ACCESS
CH.1
CH.2
TDMA CH.
SLOT 1 SLOT 2 SLOT 1 SLOT 2 SLOT 1 SLOT 2 SLOT 1 SLOT 2
ECONOMICS OF THE EVOLUTION
• SPECTRUM is a valuable “resource” now ☺
• 2 simultaneous channels in a single narrowband FM ch.
• Better Audio Quality @ Weaker Signal Strengths
• Ongoing debate on coverage improvement !
• ~40% improvement in Battery Efficiency
• Intermittent transmission in Timeslots
• IP based interconnectivity
• Everything in the network speaks the same language
DIGITAL RADIO MODES - COMPARISON
FEATURES / SYSTEM DMR DSTAR SYSTEM FUSION NXDN FREEDV
Developer / Promoter ETSI JARL / Icom Yaesu Kenwood VK5DGR + hams
Multiplex Method TDMA FDMA FDMA FDMA TDMA*
Modulation 4FSK GMSK C4FM 4FSK DQPSK
Vocoder AMBE+2 AMBE+2 AMBE+2 AMBE+2 Codec2
Transmission Bitrate 4.8kbps x 2 4.8kbps 9.6kbps 9.6kbps 1.4kbps
NETWORKED RADIO SYSTEMS
• Radio over IP networks
• Linking multiple repeaters across the world – DMR-MARC,
BrandMeister, etc.
• Enhanced Echolink-like functionality
• Worldwide Calling Channel !!
• Roaming
• Continous exchange with Repeater autoswitch on common
Talkgroups
• Remote IP based Programming
• Radios and Repeaters can be programmed over air / IP networks
• Data exchange modes
• SMS Messaging
• Location Beacons with GPS attachment – APRS gateway
http://hose.brandmeister.network – Listen Online!
NETWORK TERMS AND DEFINITIONS
Term Defintion
Timeslot (TS) A brief interval to which a DMR radio, especially a repeater, accepts data from
another radio. For DMR there are two (2) 30ms time slots.
Talkgroup Virtual Radio Channel, typically assigned by geography or language. Dynamic TG are
(TG)/ Reflector assigned to a channel on keying PTT for a time period. Static TGs are fixed on TS.
Color Code A number that is analogous to the PL or CTCSS tone used during analog FM Analog
Operation (defaults to value 1 mostly)
C-bridge A Server that bridges together regional DMR Networks / Brandmeister
DMR ID A unique number assigned to each radio on the DMR Network. Also known as
“Subscriber ID” or a “Radio ID”
BER Bit Error Rate – Ratio of bits successful decoded without error. Equivalent of SNR in
Analog communications.
CPS Short for Customer Programming Software, which is the software used to program a
DMR Radio.
DMR PORTABLE RADIOS
TYT MD-380 Radioditty GD-77 Anytone AT-D868UV
VHF or UHF Single band VHF/UHF Dual band VHF/UHF Dual band
~90 USD ~100 USD ~160 USD
DV HOTSPOTS
DVMega
Shark openSPOT
VHF/UHF Dual band
Supports DMR/Dstar/SystemFusion
Pluggable on Raspberry PI
USB Powered, 20mW output on UHF
~120 GBP
~190 Euro
DV4Mini
Supports DMR/Dstar/SystemFusion
MMDVM / ZumSpot
USB Powered, 10mW on UHF or VHF
VHF/UHF Dual band
~ 130 USD - UHF
Pluggable on Raspberry PI / Arduino Due
~150 USD - VHF
~80 - 100 USD
PI-STAR DIGITAL
VOICE DASHBOARD
• Software running on Raspberry PI
• Management of Digital Voice Modes
for MMDVM Modem
• Supports DMR, Dstar, YSF, P25, NXDN
• Live monitoring of RF / IP Gateways
• TG/TS/Call/Duration/Loss/BER reports
DIY / HOMEBREW…
Monitoring with RTL-SDR dongles using DSD decoder plugins
https://www.rtl-sdr.com/rtl-sdr-radio-scanner-tutorial-decoding-digital-voice-p25-with-dsd/
DIY / HOMEBREW…
Using FM Discriminator Output from Analog Radios for building Repeater / Hotspots
http://www.mountainwestdmr.org/styled-22/styled-3/files/notes-for-interfacing-the-
cdm-1250-uhf-radio-with-the-mmdvm-board.pdf
DIY / HOMEBREW…
SM1000 SmartMic - David Rowe VK5DGR / Rick Barnich KA8BMA (open design)
http://www.rowetel.com/sm1000.html
