Digital Radio Mondiale (DRM)
Digital broadcasting on shortwave and medium wave, sending near-FM-quality audio.
DRM sounds like a flat, steady rush of hiss, about 10 kHz wide, with sharp edges and no voice or tones in it, like loud static that never changes.
What does it sound like?
A flat, steady block of hiss about 10 kHz wide, with no voice.
Who uses it?
International and national broadcasters in some countries.
Where and when can I hear it?
Shortwave broadcast bands, 3-26 MHz.
How to recognize it
DRM (Digital Radio Mondiale) spreads its data across many closely spaced carriers at once, a technique called OFDM. Played through an ordinary AM or shortwave radio, all those carriers add up to something that sounds just like noise. What gives it away is its shape: a flat-topped block of even hiss with steep sides, sitting exactly where a broadcast station would be, and switching on and off on the hour or half hour like a program schedule.
On shortwave the block is usually 10 kHz wide, sometimes 5 kHz. A narrow receiver filter shows only part of it, which makes it sound like plain static.
Easily confused with:
- Ordinary noise or interference: usually uneven, drifting or pulsing rather than a clean rectangle.
- Over-the-horizon radar: also wide, but pulsed or sweeping with a rhythm.
- HF data systems such as STANAG modems: narrower (about 3 kHz) and in utility bands rather than broadcast bands.
Where and when to hear it
DRM appears in the shortwave broadcast bands (such as 25, 31 and 41 meters) and on some medium wave stations. Broadcasters that have used it include All India Radio, which built the largest national network, Radio New Zealand Pacific, China National Radio and several European international broadcasters. Schedules change each broadcast season, so check a current listing before searching.
A version called DRM+ is designed for the VHF bands, and trials have run in several countries.
On a waterfall display, a DRM station is easy to spot once you know the shape: a bright, perfectly even rectangle, with a few slightly stronger lines inside it (reference carriers used by receivers to lock on). Signal strength matters more than with AM: a DRM signal either decodes cleanly or drops out entirely, with little in between.
A little history
The DRM Consortium was founded in 1998 by broadcasters and manufacturers who wanted to give the bands below 30 MHz, where AM had been used for a century, digital sound quality and data services. The International Telecommunication Union endorsed DRM for broadcasting below 30 MHz in 2001, and ETSI published the system specification the same year.
Besides audio, DRM can carry station information, text news through a service called Journaline, and emergency warnings. Its main obstacle has been the scarcity of affordable receivers outside a few markets.
Common questions
Is it legal to listen to DRM broadcasts?
Yes. DRM is public broadcasting meant for anyone to receive; you just need a receiver or software that supports it.
Why does DRM sound like static?
The audio is sent as compressed digital data spread across many carriers. An analog radio cannot decode it, so it plays the combined carriers as an even hiss.
What do I need to hear DRM?
A dedicated DRM receiver, or a software-defined radio with free decoding software such as Dream. The receiver must pass the full 10 kHz width of the signal.
Is DRM the same as DAB or HD Radio?
No. DAB and HD Radio are digital systems for other bands; DRM was designed for shortwave, medium wave and long wave (and, as DRM+, for VHF).