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Digital Radio Mondiale

Shortwaves of the XXIst century

At the end of the XXth century we entered into the Information Age, and we were the witnesses of the widespread of digital technologies like the computer, the CD, the GSM, the DVD, the MP3 and other digital packet. Suddenly the radio of our parents looked old-fashioned. Imagine : it was made in the last century, Hi!

In a similar way, and as surprising it was, in September 1996 the Digital Radio Mondiale, DRM for short, emerged from an informal meeting in Paris (F), between some of the large international broadcasters and broadcasting equipment manufacturers. These included representatives from Radio France Internationale, TéléDiffusion de France, Deutsche Welle, Voice of America, and Thomcast. 

During this meeting, a consensus emerged that unless something was done, the days of national and international broadcasting in the AM bands below 30 MHz were limited. 

The DRM Consortium formed in 1998 when a small group of pioneering broadcasters and manufacturers joined forces to create a universal, digital system, DRM, for the AM broadcasting bands in HF, this wide band of frequencies including short waves, medium waves and long waves. Since then, DRM has expanded into an international consortium of more than 70 broadcasters, manufacturers, network operators, research institutions, broadcasting unions and regulatory bodies, with members represent more than 25 nations. Today DRM’s membership is rich in its diversity, with members live in countries as varied as Australia, China, Ecuador, Finland, France, Germany, India, Japan, Luxembourg, Nigeria, Spain, Tunisia, the U.S.A. or the United Kingdom.

The DRM standard

DRM is not a registered trademark. This is a standard entered into force as of January 30, 2003. At this time the International Electrotechnical Committee (IEC) gave DRM its highest stamp of approval, the International Standard : IEC 62272-1, following the DRM specifications PAS 62272-1 approved in 2002.  

BCE's DRM antennas at Junglinster, LX. 600 kW on 234 kHz and 70 kW on 6095 kHz (inserts).

Indeed, in 2002 DRM received endorsement by the ITU for all three broadcasting bands (SW, MW and LW) below 30 MHz. The new ITU Recommendation BS1514-1 states that DRM is an ITU-R Recommendation for all the broadcasting bands spanning 150 kHz to 30 MHz. No other digital radio system has received such broad recommendation and for all three bands by the ITU.

In addition the European Telecommunications Standards Institute (ETSI) published a Technical Specification of the DRM system in September 2001. The document is called ETSI TS 101 980 V1.1.1 (2001-09) and define the DRM system specifications.

This new standard does not mean that DRM is reserved to broadcasters and fixed services. On the contrary ! This standard means that DRM is non-proprietary, with the ability to use existing frequencies and bandwidth across the world, and therefore interest much the radio amateur community.

The DRM signal fit in a bandwidth of about 10 kHz (against about 3 kHz for SSB phone), although there is a wide version that spreads over 20 kHz and a narrowband version 5 kHz wide, the wider offering the best audio fidelity.

DRM uses the COFDM (Coded Orthogonal Frequency Division Multiplex) modulation. The signal is modulated on a great numbers of carriers (max. 460) thanks to the FDM technique. This allow an emitter to avoid problems with the differents paths that a wave can follow to reach a receptor. Additionally DRM can integrate data and text. To code the audio signal DRM use several systems : MPEG4 AAC when there is a mix of speech and musical content and MPEG4 CELP when the signal contents only a speach without musical content. DRM is in fact an application of DAB. This concept is used in the DVB standard (Digital Video Broadcasting) too. 

Radio amateurs also use digital audio and video !

Beside broadcasters, hams actively participate in experiments developing the use of digital voice and video over ham techniques, and ARRL in particular has created a Digital Voice Working Group in that purpose.

Indeed, digital transmission have many advantages of analog transmission : the reception is error free, noise-free and the listener can potentially receive simultaneously audio, voice and data. There is only one drawback, the bandwidth occupies 10 kHz or more vs. 3 kHz for SSB phone.

To get a quality voice signal data rate must be of at least 3600 bits/sec or higher. The modulation uses sophisticated formats like orthogonal frequency-division multiplexing (OFDM) with multiple subcarriers modulated at low bit rate using phase-shift keying (PSK), quadrature amplitude modulation (QAM), etc. This modulation is combined with error detection and correction, so much techniques necessary to transmit signals in a dispersive media as HF. The main advantage is to be able to transmit on HF digital information at a rate that can reach 5400 bits/sec. 

Much less known due to its young age, the Digital Amateur Radio Television (DATV) is the digital evolution of SSTV. It will be on board the European Columbus module of ISS from 2007 in framework of ARISS activities.

Why DRM ?

Up to now broadcasters use several standards, DAB (Digital Audio Broadcasting) using the Eureka-17 standard for FM broadcastings and Ibiquity IBOC (In-Band On-Channel) for AM broadcastings, recently activated by WOR Radio in New York. Both standards are used worldwide but DRM appears as the only one standard recognized internationally for HF use. 

DRM will progressively replace classic AM broadcastings, and will become the "digital AM". Indeed, this new standard offers a higher listening quality : RFI, noises and fading practically disappear. 

To check : DRM Logbook

Listen to DRM !

Audio samples of two speeches (UK and F), a sound and a demonstration broadcasted by DRM stations on shortwaves (.MP3 of 443 KB, 378 KB, 1.4 MB and 1 MB).

The quality of signals can be modulated depending of the information to transmit, i.e. the language of the transmission for a speech. Without being equivalent to an audio CD, DRM offers the same listening comfort and quality as FM. We can quasi speak of HiFi shortwaves !

Nowadays, the FM band is limited between 88 - 108 MHz and is heavily occupied by more broadcasters than there are channels available. For ITU authorities, assigning bandplans worldwide is became a true challenge when they must satisfy requests from all services involved. In this context, DRM is an interesting alternative. According the consortium, DRM will revitalize the AM broadcasting bands below 30 MHz in markets worldwide. In parallel the regulation has to evolve to take in account this new broadcasting mode.

Actual emitters working in short, medium and long waves count by thousands as Klingenfuss could confirm, and these companies invest much money in their installation to ensure the best coverage over their country or abroad. Hopefully DRM allow the reuse of these installations with some modifications. 

For the listener, DRM consortium insists to the fact that receivers have to be at low cost to attract customers, the reception quality must be improved without change to existing listening habits (same frequencies, same listening conditions - fixed, portable and mobile radio - and same listening environment - indoors, in cities, in the country...), receivers must yield low energy consumption, they must be easy to use and tuning, programmes various and taking advantage of the full capabilities of new digital features. 

Typical flat-top waveform of a DRM broadcast from Deutsche Welle radio recorded with Merlin's Communications software provided by DRMRX.

The advantage for the manufacturer is that DRM increases the longevity of AM technology while opening new opportunities. This new technology also increases the market potential for transmitting and receiver systems. And last but not least, it optimises return on investment and other financial aspects. 

With time, DRM estimates that people will replace about 2.5 billion receivers with digital AM receivers ! 

At last for the broadcaster DRM ensures the continuing use of existing transmission systems and a more efficient use of existing frequency planning as well as a better control of coverage area and short-term flexibility. 

Of course the broadcaster will provide a better audio quality for listeners, wherever they live, and will probably see an increasing of his audience interest, resulting from audio quality improvement and additional services. In fact all active participation in the development of DRM gives the opportunity to contribute to the implementation of "digital AM" radio.

Beside the ambitious project of its conceptors, DRM offers the opportunity to broadcast textual messages like does RDS in FM. It will also automatically switch of frequencies to help users to continuously listening to a program whatever the propagation conditions. At last, DRM will support transmissions in mono, dual mono or stereo. This is already the second generation of DRM, which first products were available at Christmas 2003.

A soft transition

DRM will allow to answer to the increasing demand from all services working in HF. But it has also to take into account a time of transition for all classic AM users. It is out of question to take new channels in a spectrum already widely saturated.

Therefore DMR has decided temporary to allow emitters to work in both analog and digital in the same channel, this is the "simulcast". Depending the evolution of markets, DMR will progressively open all the channel to digital transmissions, this is "multicast", what will increase drastically the emissions quality, the numbers of new services available and maybe to... multimedia.

Printscreens of DRM emissions captured with a beta release of Merlin software provided by DRM Software Radio. At left the BBC signal with attached data. At center the signal-to-noise ratio of RNW radio signal captured in the USA with the WinRadio G-303i radio card. Very strong until 0h15 UTC. At right a transmission not synchronized yet broadcasted in Jakarta. Documents from Wolfgang Tute.

Upgrade your old HF receiver to DRM

To please everybody the first digital receivers will have to support both analog and digital broadcastings. But for our concern, it is not necessary to sold our current AM radio to buy an "AM digital" stamped DRM. Indeed, we can modify any recent analog radio, including you old HF receiver, to make it compliant with DRM. The main modification consists to widen the Intermediate Frequency (IF) bandwidth to about 20 kHz. Any commercial front-end with an IF of 455 kHz or even 10.455 MHz should be usable by adding a 455 kHz (or 10.455 MHz) to 12 kHz adaptor (assumed the receiver bandwidth is sufficient for a DRM signal).  This interface is called a downconverter. 

Now that your receiver is upgraded, you need a decoding DRM software and a computer. Today DRMRX through the project "Dream" sells a processing software under the GNU General Public License for 60 € or $70. Due to the intensive FFTs computations requested to synchronize the frequency, you need a Pentium PC running at 500 MHz or faster equipped with a sound card to process the digital signal. Documentation of receiver modifications for DRM reception can be found on DRMRX website. 

One of the first receiver to use this hybrid technology is ICOM PCR-1000, a pocket stereo shortwaves receiver able to receive AM, FM, USB, LSB and CW modes. It comes with a serial and a BNC port to link it to a computer running the DRM processing software (e.g. Dream or Talk PCR). Decoding is automatically done thanks to the optional DSP module. To work properly you have only to set the ICOM receiver in USB mode via the DRM software, set the filter to 50 kHz and shift the receive frequency 12 kHz up. You must switch off the AGC and sometimes the attenuator, the squelch and the optional DSP by pressing some buttons on the graphic user interface (GUI) reproducing a typical DRM receiver as displayed below.

At left, WinRADIO WR-3000i GUI is a typical DRM software running on a PC. This one is tuned on VHF bands. At right the GUI of the WinRADIO card G303 tuned on 6095 kHz where Radio Luxembourg expriments its first DRM broadcasts. Dream and Talk PCR software count among competitors of WinRADIO.

As time running, new manufacturers are involved in this technology and their products are always appreciated. WinRADIO, an Australian manufacturer, sells several radio cards like G-303i to install in a PCI slot of your computer ($500). A DRM demodulator is currently programming and soon available as a plug-in. This digital radio is able to receive all frequencies between 9 kHz and 30 MHz in most modes (AM, FM, USB, LSB, CW). Other DRM cards cover V/UHF and SHF frequencies up to... 4 GHz if necessary !

Several other manufacturers begin to sell DRM radio receivers to name Coding Technologies, Mayah (DRM 201D), Ten-Tec (RX-320D), and FhG AOR Japan (AR7030).

Now in emission !

Since 2005, FlexRadio Systems, an US manufacturer, sells the first software defined transceiver compatible with amateur modes (SSB, CW, AM, FM, RTTY, PSK) and DRM : SDR-1000. It works on both HF and VHF bands with an output power of 100 W in HF and 50 W in VHF. It looks like to a passive peripheral, a black box standing on your desk totally controlled by a software named PowerSDR, for now only accessible to computers running Windows XP Home Edition with Service pack 2. It price starts at $1375 (without PC, sound card, antenna, antenna tuner and shuttle-pro controller. Fully operational with a computer and a dipole or a vertical, it costs about $2500).

FlexRadio encourages programmers to enhance the open-source code. The GDI is written in C# (C-sharp) while the DSP is written in C (shared source with a Linux version). The PowerSDR source code is available free from the FlexRadio website's download page.

The future is really digital !...

For more information

DRM organization

DRM Software

DRMRX - Sofware and forum

DRM Transmissions

Talk PCR (DRM software)

Broadcasting Center Europe

QoSAM

Eureka projects

RadioMondo

VT Merlin

WinRADIO

FlexRadio Systems

AOR UK

Sat-Service Schneider

QST October 2003, ARRL (DRM)

QST October 2005, ARRL (FlexRadio)

Antennas of an AM broadcaster.

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