Digital Radio Mondiale, an alternative to HD radio?

DRM logo

Could be.   Digital Radio Mondiale, or DRM, is a modulation scheme that a group of broadcasters and transmitter manufacturers have been working on since about 1997 or so.  There are numerous shortwave broadcasters; the BBC, the CBC, Deutsche Welle, Radio France Internationale, the VOA, and others have been using DRM on shortwave for several years now.  I can state that the shortwave DRM system works well, I have a software decoder and use the sound card input on my computer to decode and listen to DRM shortwave broadcasts.

The goal of DRM is to establish a worldwide open standard for digital broadcasting in the LF, MF, HF, and VHF bands.  In the early years of development,  DRM was designed for digital broadcasting on bands below 30 MHz.  This system is now known as DRM30.  Since then, the DRM consortium has expanded that to the VHF band (up to 174 MHz)  as well (meaning where the current FM band is located) and has called that system DRM+.

DRM uses COFDM (Coded Orthogonal Frequency Division Multiplex) modulation, which is the same as IBOC HD radioTM.  This is a robust modulation system that employs multiple carriers at lower power (than an analog carrier) spread across the entire allotted bandwidth.

One of the claims is  DRM transmits less power and is more energy efficient.  In general, digital radio modulation does transmit less power, that is true.  However, transmitters have to be run more linearly for digital due to the increased bandwidth.  This may not translate to greatly increased efficiency from the AC mains to RF standpoint.  Because of that, there is more waste heat, and thus more air conditioning is needed to cool the transmitter room.

Some of the advantages of DRM over Ibiquity’s HD radioTM are:

  • Open source system.  Royalties are paid by the transmitter manufacturers only (and to date, most major US transmitter manufacturers have already paid these).  There is no royalties paid by the broadcaster to install DRM or by the consumer when purchasing a DRM-capable receiver. One company does not own the rights to the modulation system for all the broadcasters in the country.
  • Universally standard; accepted by the European Telecommunications Standards Institute (ETSI), International Electrotechnical Committee (IEC), and the International Telecommunications Union (ITU).
  • The CODEC is HE-AAC 4, which is widely used worldwide.
  • DRM30 and DRM+ fit into existing band plans and will not interfere with other users on adjacent channels.  DRM30 is designed for 9 KHz channel spacing and DRM+ is designed for 100 kHz channel spacing, all of which comply with existing FCC regulations.
  • Standardized receiver profiles are things that must be included in all DRM receivers. There are several advanced options as well, such as a media-rich system that includes video.
  • DRM+ has several added features: DRM text, which is similar to RBDS.  EPG or electronic programming guide, which shows what is coming up next and a searchable schedule of when programs may be heard out to seven days.  Some DRM+ receivers will have a TIVO-like recording device that allows the user to record programs and playback later.
  • Traffic reporting and routing

In addition to that, DRM30 stations have the ability to transmit low frame rate H. 264 video.  This is a distinct advantage for short-wave stations that are seeking a way around firewall blocking.  The video image is small, 176 x 144 pixels and it is 8 frames per second, which is about as good as can be expected using a 9 KHz channel.

In some cases, DRM is capable of a hybrid mode (ed note: DRM calls this “Simulcast mode”), but what have we learned about hybrid mode digital radio:  It doesn’t work very well. In short, it would be better if DRM were employed in the digital-only mode.  To many, this is a distinct disadvantage, but I don’t see it that way.  There have been many that have made the IBOC rollout/FM broadcasting rollout analogy.  Frankly, those arguments don’t hold water.  When FM was introduced, no attempt was made to shoehorn it into the existing AM (Standard Broadcast) band, it was not designed to interfere with other stations or itself, power levels were sufficient for good reception using existing technology, quality over AM was markedly improved and programming was often separate (simulcasting with existing AMs did not start until later).  My point here is that any digital broadcasting should be introduced on a separate set of frequencies.  Some have proposed using TV channels 5 and 6, which makes some good sense.  Whatever the outcome is, we have learned, the hard and expensive way, that hybrid digital broadcasting does not work well.

A brief video about DRM30.

Currently, DRM30 is only allowed on shortwave broadcast frequencies in the US.  I asked a product development engineer from a major reputable broadcast transmitter manufacturer about this, and his response was:

  • Medium-wave broadcasting in the US already has HD radio, so the FCC would be disinclined to allow a new standard
  • One might be able to apply for an experimental license to broadcast DRM, but it would likely have an expiration date
  • It is possible to operate DRM in a hybrid mode on the AM band and occupy the same bandwidth as HD radioTM (30 kHz), it might also be possible to squeeze that down to 20 KHz.
  • Most modern (read: solid-state) AM broadcast transmitters should be able to transmit DRM without modification (antenna systems may be a different matter).

It might be fun to apply for an experimental license to broadcast somewhere in the 1600-1700 KHz range with DRM30 only and no analog modulation, except for an hourly station ID in Morse.  A 1/4-wave tower in the middle of that band would be 141 feet tall.  With the use of a skirt, a grounded tower can be employed.  That and a few above-ground radials and the system would likely be pretty efficient.  Part of the experiment would include driving around and taking signal strength readings while recording the programming material.  This would give some real-world testing on how the system would perform in widespread use.

Of course, this would require a major about-face by the FCC, which is not likely unless someone there grows or somehow acquires a backbone.

Some people question the need to do any type of digital broadcasting.  I am a realist, in one way, shape, or form, digital radio broadcasting will (or already is) take(ing) place.  It would make the most sense if the best system were used, which is not necessarily the first system proposed.  The big question is, will today’s terrestrial broadcasters be involved, or out of business?