Digital Voice applications and Ham Radio

a loose (messy) collection of notes

Codec | Multi-Mode | D-Star | APCO-25 | DMR | Yaesu


Update 2015

I started a VOIP page in 2007, that quickly started to include Digital Voice/Radio format.  I have added links and documents over time, but the following intro paragraphs have pretty much not changed, pay specific attention to the "Toward Software Defined Radios and Digital Voice" part that has also remained unchanged since 2007.

I have since separated my VOIP and digital voice pages.   Therefore some things have moved.  I have also placed the codec and multi-mode/bridging sections on top as I feel there are areas that need a priority.

More recently there are some interesting things that I encourage you to review.  Basically they all revolve around multi-mode open source and interoperability.  This is the logical future as amateur digital voice is already fragmented enough. 

Bruce Perens, K6BP talk on AMBE Exposed from the 2014 DCC - (presentation pdf)

The 2012 webinar, where Chris Imlay W3KD and Ed Hare W1RFI predict and speculate what ham radio will be like in 25 years.

A few new exciting new developments that have been works that are worth keeping an eye on:

- In May 2012 is from Bryan Hoyer, K7UDR / NW Digital Radio,  a new design approach to a high speed UHF data radio, the proposed UDRX-440. (yahoo group)

- In May 2014 is from Jerry Wanger, KK6LFS / Connect Systems, a new design approach to a multi-protocol Digital Voice radio, the proposed CS7000. (yahoo group)

- In April 2015, in Ham Radio Now episode 193 we learn about VHF/UHF TDMA radio (SM2000) developments by David Rowe.  And in episode 194 we hear more on Bruce Perens' Algoram company working on VHF/UHF TDMA radio (Algoram, Katena, Whitebox) developments.

- In July 2015 a German group (Stefan DG8FAC, Torsten DH1HT, Kurt DJ0ABR, Hans-Jurgen DL5DI and Michael DJ2VA- same group that developed the DVRPTR) introduced the DV4mini.  A multi-protocol (D-Star and DMR initially) Digital Voice Access Point.  A few months later a Florida/US reseller, Wireless Holdings headed by Ulrich, AG0X/DH6SAB appeared and subsequently announced the DV4mobile.

So far, D-Star, P25, System Fusion, NextEdge/IDAS are pretty much all designed around the age old concepts of FM.  I think of them as digital modulation on top of a FM signal.  TDMA as used in DMR/MotoTRBO is quite different.  

Ultimately I think CDMA is the way to go, due to the Carsons rule impeding the data rate that is achievable even on conventional wide band channel. Getting away from channelized pure FM radio is really the only way around that. But CDMA is totally incompatible with existing band plans on any populated bands. So TDMA is the next best in my opinion.

I think each digital format so far has some pluses, so the ultimate is the combine those into a HT specifically for hams. 

Callsign routing, but also automatic replies from the radio. (D-Star's callsign routing is a blind thing) As in the ability to tell if the remote radio is on (think ping) And if not, ability to leave a voicemail message on a repeater, that they will be alerted to when they turn their radio back on. (just like cellular).

APRS like GPS reporting, but if we can get an Android interface, there can finally be some open street maps on the thing instead of a dot and line/ Atari graphics style display.

TDMA "time-slice" modulation that will allow for "on-channel" repeaters (think repeaters without a duplexer). TDMA opens the possibility to in-band repeat using the other time slot though your car or any other radio in range when you cannot directly reach your destination. (TETRA calls this a Direct Mode Repeater, or think of a real time digipeating/Mesh concepts). Ability to effectively traceroute you callsign TDMA routed conversation/call. That all DMR radios don't natively support something like the TETRA Direct Mode/Dual Capacity Direct Mode is a big oversight in my opinion.  

Open codec! Enables the ability to transcode to other standards such as SIP/ulaw etc, for Asterisk interconnection possibilities, etc. (Or maybe the patent will expire before we ever see this in a HT, making this a moot point). Ability to control all functions of the radio via a PC, think CIV/CAT etc.

Background - The future of two way radio is digital.

As of 2007, TV broadcasters in the other areas of spectrum are required to be full digital and shut down their analog transmitters in Feb. 2009.  The only spectrum broadcasters are required to vacate are channels 64 thru 69 that will become the new "700 MHZ band" that is being auctioned off by the FCC.  The vacated areas of this spectrum will be utilized for: Public Wireless deployment (Cellular/PCS); A wide-band private data network that will be shared between public safety and paying customers; and new spectrum for public safety that will butt right up to the re-located NPSPAC National Public Safety Planning Advisory Committee band being moved to 806-809/851-853 by Sprint/NEXTEL.  All non-public safety stations to operate on channels with a bandwidth of 12.5 kHz or less beginning January 13, 2013. Until 2013 (maybe), public safety users may continue to use 25-16 (wide band) kHz equipment. Phase 2, which becomes mandatory (maybe) in 2018 would require radios capable of operating at 6.25 kHz. (Digital Non-analog FM). The future of two way radio is digital, and we must also advance in this direction. The digital premise is that it generally allows more use in a more efficient/flexible use of band space.

A process of "refarming" the informal name of a notice and comment rule-making proceeding (PR Docket No. 92-235) opened in 1992 to develop an overall strategy for using the spectrum in the private land mobile radio (PLMR) allocations more efficiently to meet future communications requirements.  The FCC created mandates for the two-way radio equipment manufacturers. In 1997, all new two-way radio models had to be capable of operation on the "new 12.5 kHz narrowband" channels. This is often called "dual-mode" equipment since the radio can accommodate both narrow- and wide-band channels. The idea was to begin to move gently toward narrowband channel operation over time. At that time, the FCC did not create any mandates to remove older wideband radio units from service or require you to use a new narrowband channel.

The Part 90 LMR narrowbanding mandate was released 12-23-2004 by the FCC for all Part 90 business, educational, industrial, public safety, and local and state government two way radio system licensees currently operating legacy "wideband" (25 KHz) voice or data/SCADA radio systems in the 150-174 MHz (VHF) and 421-512 MHz (UHF) bands.  The executive summary of the FCC order establishes January 1, 2013 deadline for migration to 12.5 KHz technology.

Hams benefit because a lot of used equipment  will start showing up. Oddly enough while  most ham repeater coordination bodies, coordinate / assume traditional 16 kHz wide-fm bandwidth, D-Star boasts it's spectrum efficiency with a 6kHz bandwidth for ham radio.


While that is nice, it's not necessary at all.   Hams are not bound by these narrowband rules, refarming nor will there ever likely even ever be a rebanding.  We have oodles of spectrum available to us, most of it un-used.


What is actually disappointing about D-Star is that  it's only a 4800 baud total data stream equivalent signal.  2400 bps is reserved for actual digital voice, 1200 bps is reserved for FEC (forward error correction)  on the digital voice.  (This is for callsign and short message data.)  1200 baud is reserved for serial data low speed digital data .  (This is for APRS, and text messages/text query's.)  The sad part is 1200 baud data is what we were doing in the 1980's. 


So if 4800 baud can fit into a 6kHz bandwidth, we could have had a 12800 (12.8k) baud total data stream equivalent signal fit into our existing 16 kHz bandwidth plans.  This could have left us with 9.2k left for data.  Or at the very least more could have been given for the digital voice codec, so that we could use other license free-codecs that sound more natural.

Toward Software Defined Radios and Digital Voice

Obviously you gravitate towards things.  You don't just expect to, like a light switch, convert everyone to purely digital radio.  

It would be logical at this day in age if you're planning on upgrading a repeater system to ensure that it can repeat analog and some form of digital.   P-25 systems and Motorobo systems can do just this.  Just as if you are considering a new HT or mobile to purchase something that is digital capable like the IC-91AD or the alike.

Technology is ever changing, which makes standards hard to set.  This is why open standards are so very important.  It expedites production and advancements , as you are effectively working together or sharing information.  Be wary of  any thing proprietary, as this impedes technology and is terribly unhealthy for the hobby.  

Protocols and standards need to be dynamic as possible to avoid equipment obsolesce.  This is where the software defined radio (SDR) concept is key.  However once again between here and there, manufactures should highly consider flash/field upgradeable firmware.

Just about everything has this, from phones to PDA's to routers.  An upgrade can fix a bug or give you added functionality.  The most classic example I can think of is the Linksys WRT-54G.  They grasped the open source concept and made a product that so many people have written after-market firmware for that has unlocked a wealth of added functionality.

Why don't we have more of this?  We are hobbyist and tinkerers that are supposed to be advancing the radio art.    Societies electronics evolvement has made traditional homebrewing difficult. Components are smaller and harder to work with, things are designed more throw away. However homebrewing should and will continue. It will evolve to a more modular and software level than component level.  As things progress increasingly more digital, the emphasis need to be on firmware upgradeable, open source, and user end flexibility. 

Yeasu and others seem to rush radios to the stores probably to beat the competitors, but they often suffer some firmware bugs.    The only way to have these resolved is to send the radio in.  Unless others follow in the footsteps like Kenwood apparently did.  

In summary an emphasis should be on dynamic protocols, and products that provide a capability bridge as well as upgradeable platforms.  Products that lack in these key areas are potential road blocks to the future.  I'm certainly not buying expensive radios every year, so a little foresight is all we need.

Having systems that are open to 3rd party developers (think: the best-selling router of all - the classic WRT54G), have an active developer and user community, and use open protocols have the best chance of succeeding. Hams like to tinker and also to have someone else to talk to when they need to test their tinkering.

Be wary of any product that isn't built with dynamic architecture.   Built-in obsolescence or proprietary features are excuses to force acquisition of new products.

DV Codec Related:

- AMBE vocoder from Digital Voice Systems Inc (DVSI) is used in many digital two way radio platforms. It's $150K if you want the software source but they do offer a single chip solution for $20 single quanity and are happy to sell to hams.

- Early on in 2006, Bruce Perens, K6BP, amateur radio and open source advocate voiced concerns about D-Star’s use of a proprietary vocoder. Asking; does it really fit into the spirit of the hobby? Bruce makes a strong argument that an Open Source vocoder needs to be developed.  In May 2008, he announced that he will investigate the development of an alternative codec. The Codec2 Project: Next-Generation Audio Codecs and Vocoders for Two-Way Radio. In August 2009 David Rowe, VK5DGR (, began designing and implementing a replacement codec under the GPL.  “Proprietary codecs typically have small, novel parts of the algorithm protected by patents. However proprietary codecs also rely heavily on large bodies of public domain work. The patents cover perhaps 5% of the codec algorithms. Proprietary codec designers did not invent most of the algorithms they use in their codec. Typically, the patents just cover enough to make designing an interoperable codec very difficult. These also tend to be the parts that make their codecs sound good.”  Patents are protected for the longer of 17 years from issue date or 20 years from filing date.


- In January 2008, a joint effort between Moe, AE4JY and Robin, AA4RC gave use the (blue) DV dongle.  Moe's site provides a technical reference document, schematic and driver source code.

- Digital Speech Decoder - An open source software package that decodes several digital voice radio formats (DMR, D-Star and P25) off a discriminator tap.   The software was unveiled by anonymous authors in May 2010.   It seems to have possibly stemmed from the May 2008 osmocom OP25 project, that provides a software IMBE voice encoder/decoder.  APCO Project 25 traces back to the early 1990's required publication of the IMBE and AMBE codec algorithms, which of course is how both projects came about.  D-Star voice support was added in 2013 to prove a point through a reverse engineering and guess-and-test, as the D-Star codec is completely undocumented. "If anybody wants to continue the research / work, I suggest you look at the osmocom GMR code that Sylvain Munaut worked on. Those phones use a similar codec - I believe with longer frames for the satellite latency. Initially he used the mbelib code, enhanced it for things like tone support, but he later rewrote the synthesis code completely. See OsmocomGMR for his presentations and source code." (per a author)  Note:  For most U.N. member states; non-commercial/research usage of patented technology is covered by exceptions on the definition of "patent infringement."  Actual practice may differ. Ref

An AMBE open source compatible codec? - KB9MWR (2010)

AMBE Proxy - idea KB9MWR (2013)

Bruce Perens, K6BP talk on AMBE Exposed from the 2014 DCC - (presentation pdf)


TIA-102.BABA - TIA Standard - Project 25 Vocoder Description

TIA-102.BABA-1 - APCO Project 25 Half-Rate Vocoder Addendum

TIA-102.BABC - TIA/EIA Standard - Project 25 - Vocoder Reference Test


The DV dongle    Developed by AE4JY and AA4RC in 2007 (~$199.00) - Support for D-Star's AMBE, uses a AMBE 2000 chip 

DVSI Products USB-3000  - DVSI Vocoders with a USB Interface (~$299.00) 

NW Radio Thumb DV (DV3000U ) - Unveiled Dec 2014 (~$119.95) 

Matrix Circuits/MoenComm - Star*DV -  Features built in speaker/mike connector. (~$129.00)

DVMEGA AMBE3000 shield - Fits on top of an Arduino MEGA (~$116.00)

digitalvoice - google group - Digital voice on Amateur Ham Radio - devoted to the discussion of digitized voice and data over analog emission modes.

freetel-codec2 - sourceforge list - 

Bridging / Multi-Mode / Reflectors:

DMR, Yaesu Fusion DN, and NXDN all use exactly the same bit rate and FEC. It's simply a matter of unwrapping the AMBE stream from whichever container format is used and wrapping it in the target format.  Going to anything else will require hardware to handle the differences in data rate and FEC.  Two of the modes could be done in software, P25 and D-Star, as the patents that cover the voice coding are expired.  Going from D-Star or P25 to DMR or Yaesu Fusion would likely have to be done in hardware (the AMBE3000R is a good candidate as it can process multiple streams), or wait till 2025.

- By September 2015 Jonathan Naylor G4KLX, had the MMDVM project underway.  It's a Multi-Mode Digital Voice Modem - a combined hardware and software development of a modem to handle all amateur digital voice modes.  This allows folks to interface to analog rigs to create higher power retro fitted repeaters capable of multi mode digital voice.

The rtpdir bridge - by Scott, K14LKF one of the first bridge solutions, to bridge EchoLink, IRLP, D-Star and Asterisk 

D-Star DMR Gateway - All AMBE/AMBE++ coding and decoding is done by the DV-Dongle/DV3000-Modem and in the repeater

Allstar-Digital - This list is for the discussions about using AllStar Asterisk as bridge between digital modes, D-Star, DMR, Fusion, etc and Analog. Think many to many.

N4IRS/DMRGateway - Gateway for Mototrbo to AllStar Asterisk (github) - Digital Voice Switch

Multi Protocol Digital Networks - Introduction, Overview and further development 

XLX Reflector -Yahoo discussion group - All mode linking reflectors 

LX3JL/xlxd - Ham radio multiprotocol reflector server

MMDVM- Open source Multi-Mode Digital Voice Modem (D-Star, DMR, Yaesu Fusion, and P25)  for repeaters / hotspots - Another G4KLX project - Yahoo discussion group


DCS (Digital Call Server) - DCS is the most modern D-STAR reflector system and in worldwide use.  Many countries use their own reflectors which differ from each other by their 3 digit number. (DCS001, DCS002 etc). Each DCS reflector has 26 rooms which are allocated to various regions of a country or continent. 

FCS - FCS reflectors are similar to DCS reflectors but planned for the Yaesu C4FM system. FCS001 and rooms 0-99.

PCS - PCS reflectors are also similar to DCS reflectors but used by the P25 system. PCS001 and rooms 0-99.

Xreflectors -  Xreflectors are the second generation of D-STAR reflectors and no longer widely in use. However in some countries like Italy they are still used as the hams have not yet agreed to a uniform concept. Also Xreflectors have less
ports over which simultaneous QSOs be run. Xreflectors are named XRF001, XRF002 etc.

D-Plus reflectors -  They were the first generation D-STAR reflector system. Although it is getting old it is still used intensively in a number of countries (mostly English speaking ones like USA, UK and Canada). D-Plus reflectors are named REF001, REF002 etc. They also use a number of ports allowing for simultaneous QSOs

DMR reflectors -  DMR reflectors consist of several regional servers that are connected with each other via a super ordinate network. Two nets exist, One based on Hytera and the other based on Motorola technology. The Hytera network is open and friendly to Ham Radio operators using the Nano-DV hotspot. The DMR-MARC network by design will ONLY allow Motorola repeaters to connect because of the proprietary IPSEC that Motorola has that lets the repeaters communicate through the C-bridges.

CCS7 (Callsign Communication System) - The many reflectors, repeaters and also Dongle users require a structured organization, so that the network technology works properly.  Developed as an optimized alternative to the G2 callsign routing system that will work across multiple digital radio formats.

D-Star Overview:

In 1998 the JARL (Japanese Amateur Radio League) started developing the D-Star specification.  It was first published in 2001.  In 2004, Icom became the first manufacture to adopt the standard and began selling capable radios.  It uses the AMBE+ vocoder which traces back to 1999.  Kenwood officially came out with a D-Star capable radio in 2016.

The first Icom D-Star radios used the AMBE-2020 chip which was Temple University 2002 ECE Senior Design Project.

One of the major down falls in my mind with the D-Star is that the D-Star repeaters is that it's Not reverse compatible with existing analog FM.  It only supports D-Star digital voice.  Where as a P-25 or DMR repeater system can be configured to repeat analog FM and P-25 digital voice.  This provides a transition opportunity for users and repeaters owners without the need to setup a whole different digital site, which may not even be an option for some clubs.

Audio samples: D-Star Icom (ID-1) Analog FM vs D-Star DVUn-decoded

Vocoder: AMBE+, Bandwidth: 6.26 KHz, Multiplex: FDM, Modulation: GMSK

Data rate: Maximum of 4.8 Kbps
Voice encoding method: AMBE+ converting at 2.4 Kbps, FEC at 3.6 Kbps

D-star is a 4800 baud total data stream equivalent signal.  Where: 2400 bps is reserved for actual digital voice, 1200 bps is reserved for FEC (forward error correction)  on the digital voice.  This is for callsign and short message data.  And 1200 baud is reserved for serial data.  This is for APRS, and text messages/text query's

D-Star Related:

- In April 2007, Moe, AE4JY unveiled a home-brew D-Star transceiver (His DVX Project).  It included schematic and source code.

- In July 2007, Robin AA4RC reminded everyone the D-Star over the air protocol is all open thanks to the JARL.  He said he understood and was working on documenting how the internet backbone and callsign routing works (

- In January 2008, a joint effort between Moe, AE4JY and Robin, AA4RC gave use the (blue) DV dongle.  Moe's site provides a technical reference document, schematic and driver source code. (more notes)To support its connection to D-Star repeaters, an add-on gateway D-Plus protocol was developed.  D-Plus also allows for gateway servers to connect two nodes together much like how Echolink and IRLP works.  

- In February 2008, Jakub Hruska unveiled his sound card based D-Star decoder (not open source though).

- In May 2008 Satoshi's GMSK node adapter (and its later, its clones) came along, letting folks build and interface to analog radios to build high power hotspots and retrofitted repeaters.  This used a CMX GMSK chip.

- June 2008, Scott Lawson, KI4LKF was looking for a way to connect open source Analog bridge software (his rptdir) to D-Star, and then later the GMSK node adapters.  The internet backbone aspects of D-Star still were not openly documented yet by Robin, AA4RC.  This led Scott to work on figuring it out. 

- In February 2010 Inet Labs/Robin AA4RC, publicly unveiled the Digital Voice Access Point (DVAP) Dongle.  This new (red) version is for use with a D-Star radio as a low power hot spot.  (Neither version's client ended up with any open source software.)

- By January 2009, Jonathan Naylor G4KLX came up with a way to to create GMSK in open source software with a sound card.  His first development (the Digital Voice package) was a GUI Linux client that would decode and generate GMSK using a soundcard and interface to a radio with a 9600 Baud packet connector. The Codec processing would is done by interfacing with a DV-Dongle.  Its design was to emulate a D-Star capable radio.

- By February 2011, a group of German hams (German group (Stefan DG8FAC, Torsten DH1HT, Kurt DJ0ABR, Hans-Jurgen DL5DI and Michael DJ2VA)  came up with the DVRPTR (Digital Voice Repeater board)  The capabilities of this board were defined in the firmware rather than hardware specific chips.  Intended to support multiple digital voice modes.

- In October 2013, Guus van Dooren, PE1PLM started the DV Mega project.  The initial goal was to develop a kit for a dual-band D-Star hot spot transceiver.  It has since morphed into a collective name for digital voice and data related kits and modules.   A whole a family of add-on boards (shields) for Arduino Uno, Arduino MEGA and Raspberry Pi for several digital voice communication standards.

CHAPTER5.pdf  D-Star Communication Between Zone Repeaters and Gateway

DSTARUncovered.pdf   D-Star Uncovered by Peter Loveall AE5PL

gmsk_tut.pdf  Practical GMSK Data Transmission Tutorial Application Notes

shogen.pdf  English D-Star Technical Specification

STD4_3C.pdf   Japanese D-Star Specification

Vocoder Redux-The AMBE-2020 - About the AMBE-2020 by Dennis, K3DX

DV-Dongle Technical Reference -

Slow Data.pdf The Format of D-Star Slow Data Version 0.2 by Jonathan Naylor, G4KLX

Nifty E-Z Guide to D-STAR Operation - A good reference

dstardecoder+dvdongle-Eng.pdf OH2LAK shows in this PDF how to use Jakub Hruska's D-Star decoder program in conjunction with the DV Dongle to receive D-Star audio off a analog radio using it's 9600 baud discriminator port.

D-Star to SIP translation - An idea for interoperability by John, K7VE to provide directed reverse autopatch by mapping callsigns to a DID number.  A powerful concept for EMCOMM and personal use..

D-Star Repeater Modifications - An under the hood look of the ID-RP2C, and block diagram of how it works.

ID-1's control command specification

Digital Data Packet Structure by Dick, KM4ML

Digital Voice Packet Structure by Dick, KM4ML

D-Star radio frame structure in DV mode - DL3OCK

D-STAR Digital Voice versus Analog FM Sensitivity.pdf D-STAR Digital Voice Sensitivity versus Analog FM Sensitivity - TAPR PSR Spring 2008 by Mark, N5RFX

D-Star Adapter Satoshi Yasuda's DV and Node Adapter - One of the construction projects is a regenerative GMSK smart modem -tailored for D-Star.  The other is a full blown adapter to turn an analog radio in to a D-STAR radio including provisions to encode/decode AMBE.  Both interface to varactor and discriminator connections, allowing you to retro-fit an existing analog radio.  It started for Satoshi by taking the UT-118 digital voice module and adapted it to work on any radio with a packet port.

Fred N. Van Kempen, PA4YBR has also announced that he too, has a working decoder.  GMSK Smart Modem controller. 

D-Star RF Characteristics - An analysis of the D-Star RF transmission  

Scott, KI4LKF's open source D-Star /Dextra work - 3 server programs that make up the "ICOM compatible" G2 Gateway.  Reflector, GMSK node adapter, DV Dongle modular tools.

Decoding D-Star / AMBE DTMF? - Can a digital pattern be recognized from the raw DV stream without the AMBE chip?

Jonathan G4KLX, started the d_star_development group for his  software and reference source code for capturing D-Star transmissions straight from the discriminator.  The group is dedicated to discussing and sharing information about implementing D-Star systems using non Icom D-Star hardware, this includes end user and repeater systems, hardware and software. 

dl5di/OpenDV - A collection of Open Digital Voice software for Amateur Radio based on Jonathan Naylor's G4KLX various projects.

QuadNet, unlike ircDDB, allows callsign routing without registration and it also allows connecting the network with gateways having an individual callsign as opposed to requiring a club callsign.  Full support for Icom Repeater stacks, Homebrew repeaters, DVDongles, DVAPs, and more.

CHIRP is a cross-platform, cross-radio programming tool. It works on Windows and Linux (and soon, MacOSX). It can program all of the ICOM D-STAR (or D-STAR-capable) radios and exchange data between them.  The CHIRP repeater tool provides a way to read and write the frequency setting of ICOM D-STAR Repeater modules from a Linux machine with the command line.  By Dan Smith, KK7DS

Bruce, KG7WI has a nice perl routine for to get and put data from/to an IC-91AD using the CIV interface that can be adapted for the IC-92AD as well.

APCO-25 Overview:

P-25 (APCO-25/Project 25) was implemented by Public Safety agencies in 90’s, and is administered/standardized by the Telecommunications Industry Association.  The first P25 radio using IMBE was by Motorola in 1996.  The IMBE vocoder traces back to 1993.  Prior to that some Motorola Astro radios used VSLEP.

Vocoder: IMBE, Bandwidth: 12.5 KHz, Multiplex: FDM, Modulation: C4FM

P25 uses the IMBE vocoder from Digital Voice Systems Inc (DVSI). It costs $150K to get the rights to play with that mode plus $5 a seat. Till recently there was no off the shelf IC to do it.  

A P-25 repeater system (usually a Motorola Quantar) can be configured to repeat analog FM and P-25 digital voice.  This provides a transition opportunity for users and repeaters owners. Though, it is not perfect.  In the business & public safety world, user radios are programmed with PL decode tones and busy channel lockout.  Hams often just encode a tone to get into a repeater and listen in carrier.  With a mixed mode repeater they will complain of hearing white noise when its repeating digital.  If not paying attention an analog user could accidentally "step on" a digital transmission.

Audio samples: Motorola P25 XTS-2500 Ananlog FM vs APCO P25 (Repeater) Un-decoded

APCO P25 Phase I is the present version that is in used across the country for Digital Public Safety, the P25 "open" standard has been reworked by some manufacturers limiting some of the standardization that the P25 was hoped to present..

P25 Phase I repeaters have the ability to function as a analog system or digital system.

P25 Presently operates via FDMA (Frequency Division Multiple Access) with the plan for P25 Phase II to use TDMA (Time Division Multiple Access), P25 Phase II will also have the capability to roll-back to FDMA for conventional emergency operations.

Phase 1 radios use the IMBE vocoder and Continuous 4 level FM (C4FM) modulation for digital transmissions at 4800 baud and 2 bits per symbol, yielding 9600 bits per second total channel throughput.  Where: 4400 baud are associated with the digital voice, 2800 baud are used for error correction on the voice signal, 2400 baud are devoted to signaling overhead.  

Receivers designed for the C4FM standard can also demodulate the "Compatible quadrature phase shift keying" (CQPSK) standard, as the parameters of the CQPSK signal were chosen to yield the same signal deviation at symbol time as C4FM while using only 6.25 kHz of bandwidth.

Phase 2 uses 2-slot TDMA and FDMA (CQPSK) modulation schemes. Phase II will use the AMBE vocoder to reduce the needed bitrate so that one channel will only require 4800 bits per second.  

- In 2008 OP25, an Australian project to investigate the security of public-safety radio communications, spawned a Software Defined Radio Receiver for APCO-25 signals. 

- In 2012 amateurs came up with their own way to link Quantar repeaters together via their V.24 modem interface using Cisco Routers.  Native Quantar linking was designed for private microwave or fiber, not IP.

APCO-25 Related:

APCO-25.pdf VHF Digital Handbook Chapter 6 excerpt for reference - includes  the anatomy of the common air interface 

Project 25 for Amateur Radio By: Mike, KI0GO - QST Sept 08

P25 Networking  Staying Digital By: WA3VV

The P25 Network Exchange – Linking Amateur P25 Digital Repeaters Worldwide - NX4Y

A Guide to ASTRO Digital Radios - Authored by r0f / Shaun 

quantar tuning.pdf Digital Narrowband P25 VHF High Band Astro Quantar Station Standardized Service & Alignment Procedure

Astro-Spectra-COS-Take-Off.jpg Astro-Spectra squelch logic take off

APCO P25 Standards.pdf APCO Project 25 Standards for Public Safety Digital Radio

APCO P25 Common Air Interface (CAI) - TIA Standard 

Understanding the Motorola Quantar V.24 interface 

A Software-Defined Radio Receiver for APCO Project 25 Signals

Eric Ramsey's Thesis-- details an implementation using PC soundcard and analog FM radio.

astro modem card.jpg Astro Modem Daughterboard information

An "amateur" P25 repeater using Maxtracs - by Tim Warth, AA2RS.

CML Microcircuits CMX7031, and CMX7041 - Datasheet for C4FM baseband data processor chip.  After some microcontroller coding, this could work similar to how the D-Star node adapters work.  (Those typically use the CMX589AP4 chip)

WVRA Quantar PL-Strip Information - Dual Mode Quantar with a stripped PL tone on hang time. - Consideration is being given to enhancing Asterisk app_rpt to support a low-level P25 radio interface.

Decoding P25 - Some miscellaneous notes on peoples efforts, and functional NAC decoder software - A full-featured open source P25 ISSI switch is clearly achievable using the open source Asterisk PBX as good framework on which to build it

Introduction to Motorola Quantar Repeaters - Local P25 Repeater Directory

Open source P25 decoder/analyzer project A project compatible with a GNU Radio or NFM radio connected to a sound card via a discriminator tap. - OP25 is a project to bring together folks that are interested in implementing APCO P25 using software-defined radio.

DMR / Mototrbo

Digital Mobile Radio (DMR)  is sometimes called MOTOTRBO.  Which is Motorola's implementation of the standard.  DMR originated as a European Telecommunications Standards Institute (ETSI) standard, first published in 2005, the same year the AMBE+2 vocoder came about.

Vocoder: AMBE+2, Bandwidth: 12.5 KHz, Multiplex: TDM, Modulation: 4FSK

The DMR Association is the industry body promoting adoption of the standard and includes these companies as members: Harris, Hytcra, Icom, JVC, Kenwood, Motorola, Tait Communications, Vertex Standard, and Zetron.

The KA9FLX repeater in Chicago, IL was the first Mototrbo/DMR Amateur Radio Repeater in the US. It was put on the air in 2008.   

There are two commercial DMR network protocols.  IP Site Connect (Motorola) and IP Multi-Site Connect (Hytera)

There are three ham radio DMR networks.  DMR-MARC, DCI and a more homebrew friendly one called Brandmeister - Amateur Radio Use of MOTOTRBO - MotoTRBO USA -- DCI

DCI MotoTRBO Ham Radio Linking Group 

The Beginners Guide To Mototrbo

TRBO Hits the Amateur Bands - By Bob Witte, K0NR - CQ-VHF - Spring 2012

GB7TD - A digital repeater - West Yorkshire engages MotoTRBO technology - RSGB RadCom - November 2013

dmr-monitor - tcpdump / windump modification for DMR-Monitor

KD8EYF/TRBO-NET - Mototrbo perl modules for ARS TMS and LRRP 

IanWraith/DMRDecode - A Java program to decode DMR radio transmissions 

on4akh/linDmrMaster - Linux DMR master server 

n0mjs710/DMRlink - Motorola MotoTRBO IPSC Client - by Cort N0MJS with the K0USY group.   (Work began in 2013)

BogdanDIA/IPSC - MotoTRBO IPSC wireshark dissector

nonoo/dmrshark - analyses the traffic, and adds extra features to a Hytera IPSC network

kb1isz/OpenIPSC - Utilities related to DMR radio networking


Terrestrial Trunked Radio (TETRA) is a European Telecommunications Standards Institute (ETSI) standard using Time Division Multiple Access (TDMA) with four user channels on one radio 25 KHz carrier.  TETRA has been in use in the Public Safety market in Europe, Asia, and Indonesia since the late 1990's.  (It's their P25 equivalent).  However it wasn't till late 2011 the FCC amended Part 90 for use in the USA.  TETRA radios can switch to telephone interconnect providing access to public telephone networks using the SIP Voice over IP standard.

TETRA is a pure digital mode, requiring a 25 kHz signal, but internally separating that 25 kHz into 4 x 6.25 supreme narrowband communications pathways.  You are likely not going to find a mixed mode TETRA radio, as it is a widely deployed European standard.  There are portals at the infrastructure level (base stations at the tower sites) that can map TETRA talk groups to analog, P25, DMR, or other system types, but again, that is done at the tower site, and not on the radio itself.

The TETRA 25 kHz signal is broken into:

1 slot, called master control, used for data, GPS, registrations, and administration
3 slots for data: voice, or data.

TETRA does support TCP/IP and UDP/IP over the radio, or other store-and-forward type data signals.  MODBUS is a favorite for SCATA type telemetry, the language of equipment like flow meters for utilities desiring water pressure information, among other things.

TETRA also supports a talk around mode, called Direct Mode (DMO) that also uses a 25 kHz channel, but only allows for a single conversation to flow… DMO works with the 4 channel pathways described above, but only one of the slots is used.  DMO also has a concept of a repeater, and the units we used could repeat at 10W in a mobile unit.  So yes, you could build up a 10W repeater, and put it on a decent antenna, say 100 feet up, and go from there.  And as the radio is a mobile, with 12V supply, you could put the mobile at 90 feet, and use 10 feet of feed line to keep those 10W close to the antenna.

TETRA versus DMR - white paper 

Comparison of DMR and TETRA

In 2011 the first two-way TETRA amateur radio contact took place in the Netherlands on 434.000 MHz.

Yaesu Digital:

During the 2011 Tokyo Ham Fair, Yaesu presented a new line of digital ham radios.  Then a short time later in late 2011, a new page on the Yeasu website titled "The Dawn of Digital Communications in the Amateur Radio World" appeared. "2012 will be a historic year that sees Yaesu lead Amateur Radio into the modern era of Digital Communications."

Vocoder: AMBE+2, Bandwidth: 12.5 KHz, Multiplex: FDM, Modulation: C4FM

Yeasu introduced radios to the ham market in 2012 based off DMR using C4FM / FDMA modulation.  Just before Dayton 2012, the FT-1DR was unveiled.  December 2012, the FTM-400DR mobile radio was unveiled.  And at the 2013 ARRL/TAPR DCC the final component, a repeater for the Yeasu digital radios, called "System Fusion" was unveiled by  Yaesu's VP for North America, Dennis Motschenbacher, K7BV.

I had a lot of hope for Yaesu, since its typically been my radio of preference, and they were the latecomer to the digital.  It even seemed like they must have read some this page.  Their repeater does analog so it does provide a transition opportunity.  The radios are firmware updateable (yet no open for third party development).  So those thing were done right, however their digital design is disappointing, as well as their internet linking tie-in.  The design took a 30 year step backwards in digital communications by releasing a design based on P25 Phase 1 but occupies more bandwidth to do less.

Audio Samples: 

SystemFusion_DN_PY2DZA_DiscrOut.wav - Raw (undecoded) 6.25kHz DN Mode.

SystemFusion_VW_PY2DZA_DiscrOut.wav - Raw (undecoded) 12.5kHz VW Mode.

Demo of the Yaesu FTM-400DR digital radio - you can compare how it sounds radio to radio in wide digital vs narrow digital

Sept 2013 System Fusion Product Bulletin - Details key features

Sept 2013 Digital Product Overview - Contains Specifications

System Fusion Introduction Presentation - As used in the DCC presentation

Yaesu Amateur Radio Digital Specifications - English version technical specifications

A Comparison of Amateur Radio Digital Voice Systems - Compares D-Star, DMR and Fusion

n8ohu/OpenSystemFusion - Source code for a series of applications for the Yaesu System Fusion Amateur Radio Digital Voice mode

hb9uf/gr-ysf - GNU radio modules for decoding Yaesu System Fusion C4FM packets

The FTM-400DR and FT1DR manuals state: the data port can be used for waypoint download, packet via external TNC and firmware upgrades.

There are 3 tiers in the DMR standard (described in ETSI technical standard TS102 361), the FT-1DR appears to be a Tier 1 product.  Unfortunately this isn't really compatible with anything else on the market, other than the dPMR products intended for licence-free applications mainly in Europe?  (maybe someone can please confirm this)

Quote from the Yaesu PDF:
"The most attractive benefit of digital communication is its ability to transfer large amounts of data. While it is commonly believed that narrowing the occupied bandwidth to efficiently utilize the frequency spectrum, is the primary advantage of Digital radio, we know that if the bandwidth is made narrower we lose the large data transmission advantage. In this situation, it becomes difficult to understand why anyone would want to use Digital communication for this purpose."

"At this point in time, Vertex Standard believes the C4FM (4-level FSK) FDMA or TDMA are the most suitable selections for Amateur radio applications. In early 2012, we will release a C4FM (4-level FSK) FDMA Handy-Talky and a Mobile transceiver into the Amateur radio market.

After our initial introduction, we plan to introduce a C4FM (4-level FSK) TDMA (2 slots) or TDMA Handy and Mobile transceiver into the Amateur market."

Quotes from the 2013 DCC Yaesu unveiling of the System Fusion repeater system:

K7BV> "We'd like to think some people will help us take this system into the future."

K7BV> "We recognize that not every group wants to buy a new repeater."  Related to that, one of the first questions asked: "Are the technical specifications available to that we can build our own hardware?" K7BV> "Its my understanding that we are going to make that available."

I don't care if it uses AMBE. I wish people would get over that. At least in this system the repeater has a vocoder capability.  What is interesting is that the end user  radios support firmware updates!!! In my opinion, what happens with that and future updates and any possible 3rd party  ones is what will determine if this is a winner or a failure.


Digital Voice Amateur Radio Association - For comparison audio samples P25, D-Star, MotoTRBO and more

There is now a new digital system called NXDN digital (aka Kenwood NEXEDGE, Icom IDAS).  Reports are that it really does a fine job, sounds better than Mototrbo and P25 Phase 1 Digital.   It really looks quite promising, cost wise as well.  Nexedge / Idas repeaters like P25 systems are also capable of mixed mode, reverse compatible with existing analog FM.   They also use the AMBE+2 codec that reportedly can fully interoperable with the current P25 IMBE standard. The AMBE+2 can also operate at half rates of 3.6 kbps for Phase 2. The AMBE+2 provides improved voice quality, better noise immunity, tone capability, and other new features. These Enhanced Vocoders significantly improve the voice performance of the P25 system, while facilitating the migration and interoperability between new and existing P25 equipment.

Vocoder; AMBE+2, Bandwidth: 6.25/12.5 KHz, Multiplex: FDM, Modulation: C4FM

Robert, N1XDN, makes available NXCore Manager open source software which implements an Amateur Radio NXDN network