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The Engineer's Notebook is a shared blog for entries that don't fit into a specific CR4 blog. Topics may range from grammar to physics and could be research or or an individual's thoughts - like you'd jot down in a well-used notebook.

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AM Broadcasting: A Rebirth?

Posted January 17, 2014 10:53 AM by Hannes

Picture this: you're an 8 year old on a Friday night in 1933, cross-legged on the floor next to your hulking, overheating Zenith console, impatiently waiting for Buck Rogers to come on the air. Fast forward to 1947, when as a young man the highlight of your week is tuning in to "watch" Jack Benny on your dial. A decade later, you're at your homebrew HF set in the basement of your suburban American home, anxiously trying to make contact with Philippine hams and dreaming about receiving that QSL card in the mail.

These very-20th-century moments depict the glory days of radio broadcasting, which has steadily declined since the advent of television, computers, and the World Wide Web. What's worse, analog enthusiasts are experiencing unbearable interference from these modern devices, making many AM or shortwave stations unlistenable. In the late-20th and early-21st centuries, however, digital broadcasting seems to have infused some life into this dying medium. In particular, Digital Radio Mondiale (DRM), a developing set of digital broadcasting technologies, has shown major promise and has been speedily adopted as a new standard since its inception.

Digital Radio Mondiale (mondiale is French/Italian for "worldwide") is also the name of the consortium which designed and is implementing the platform. Members include major international radio organizations such as Radio France Internationale, BBC World Service, Deutsche Welle, Voice of America, and Transradio (formerly Telefunken). The group's aim is to use digital audio broadcasting to efficiently improve AM transmissions without requiring a massive changeover of equipment and increased expenditures.

DRM's efforts appear to have been successful. The consortium realized that computer processing power is much cheaper and more freely available than bandwidth, so that the DRM system relies on using processing power to compress signals in order to make more efficient use of bandwidth. DRM standards give broadcasters the limited choice of three MPEG-4 codecs to encode source material for a maximum bit rate of almost 35 kbit/s on a 10 kHz channel. (For comparison, American HD Radio is capable of 20 kbit/s on the same channel width.) This results in a long-distance signal with audio quality comparable to local FM stations.

It's worth noting here that while AM broadcasting may seem hopelessly outmoded in many Western nations, it still occupies a significant hold on local and international media in less-developed countries. AM remains a go-to choice for reaching widely-dispersed populations due to the increased reach of longwave, medium wave, and shortwave transmissions. International broadcasting uses these same frequencies to export tourist information, propaganda, and patriotic rigmarole to foreign lands. Compared to modern telecommunications, shortwave requires minimal infrastructure: a couple transceivers, an antenna, a power source, and favorable atmospheric conditions are all you need to reach someone on the other side of the world. Some sources (albeit shortwave broadcasting stations) estimate that the number of active shortwave receivers tops 1.5 billion worldwide.

DRM's techniques are nothing new: Digital Audio Broadcasting (DAB) technology has been using compressed broadcasting in local European broadcasting for years, albeit with lower audio quality and little interoperability. Boons of DRM include the fact that the standard has been designed to make use of older equipment in existing stations; for example, no specialized antenna is needed to transmit the compressed signal. In addition to audio, DRM can simulcast multiple signals, including audio metadata, analog signals, and other data. Simulcasting digital and audio signals, which is impossible on most other digital broadcasting methods, is especially useful to conserve bandwidth because digital as well as analog receivers are able to pick up the same program on the same bandwidth without wasted space.

While DRM is pretty good about touting the benefits of their new technology, there have been drawbacks. Early DRM-compatible receivers (like the one at left) all required computers to operate, and while many European companies are now manufacturing dedicated DRM receivers, they remain relatively expensive (200 € and up). Very recently, there have been a string of commercially manufactured radios which provide DRM-compatible output ports. Considering the availability of open-source DRM software, this looks to be a much cheaper option.

The original DRM standard has been enthusiastically adopted by several international and regional standards bodies, including the IEC and ITU, and the U.S. Federal Communications Commission adopted it as a digitally modulated emissions standard in late 2013. DRM's development continues to march on, and the group is busy testing DRM+, which applies similar principles to local FM broadcasting. Community Media Forum Europe recently advised the EC to adopt DRM+ as a replacement for Digital Audio Broadcasting (DAB) standards for local broadcasting in Europe.

This writer hopes that DRM-compatible equipment continues to drop in price as a prerequisite for more widespread adoption. While the Internet continues to shrink the scale of global communications, I still think it might be cool to switch on the radio and hear FM-quality underground Chinese broadcasts or soft rock from India.

Image credits: Neatorama | National Association of Broadcasters


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Re: AM Broadcasting: A Rebirth?

01/18/2014 6:25 AM

DRM has been around for a long time but it seems to be an excellent technology with no market. DRM uses different techniques to DAB because DRM is designed to handle the fading and mulitpath interference that is so charcteristic of SW (shortwave) broadcasting. It works well although it cannot deliver CD quality under all fading conditions as some proponents claim.
I used to work for a SW broadcaster, we were involved with the DRM consultations and for a time broadcast some programmes on DRM as well as the regular analogue channels. Unfortunately there was no audience for the DRM (apart from other provessionals monitoring DRM broadcasts) so we stopped.

Today's SW audience is primarily rural and in the developing world. They are often poor so are very price sensitive. An entry level DRM receiver is 15x the price of an entry level analogue receiver, this is unafforable so there is no audience for DRM. Without an audience broadcasters won't use it. Without an audience the manufacturers will not invest in the mass production needed to drive the costs down.
It needs a very big player to break this vicious circle. It had been hoped the Chinese government might adopt DRM for internal broadcasts which would have jump started the market (if they had adopted an open standard and not some locked down variant). This now seems unlikely to happen.
In the meantime the market for cellphones has exploded in the developing world. These are much cheaper and more versatile devices, almost all have FM receivers built in and increasingly have access to internet based media. FM stations are proliferating as well. Although there is nothing to beat SW for broadcasting into a closed country or to remote areas, to all intents and purposes the cellphone has killed the prospects for DRM.

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