[opendtv] DRM digital radio and IBOC

  • From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 02 Dec 2006 18:20:06 -0500

Sort of off topic, for a DTV list, I've been doing a little research in DRM (Digital Radio Mondiale) and IBOC. Trying to figure out how this digital radio market will play out.


DRM was originally intended for frequencies below 30 MHz. i.e. for the LW, MW, and SW bands. It potentially could coexist with Eureka 147, the Euro DAB scheme, which operates in the L band (above the UHF band), is an older spec, but offers a higher bit rate and better audio quality.

One of the reasons why DRM chose these low freqs is that their use was declining due to poor audio quality, and yet no one out there is clamoring for these long wave bands. So why not try to revive them?

In March of 2005, the DRM spec expanded to cover frequencies up to 120 MHz, meaning it now potentially includes the FM band.

Then along comes the US proprietary Ibiquity IBOC scheme, the US as usual going its separate way, which overlaps with DRM in the MW and FM bands, and offers a simpler transition strategy. I found two countries interested in testing out IBOC: Australia and Switzerland. But I didn't find anything very up to date yet, on the results of their tests. Supposedly in Switzerland they are testing out IBOC in SFNs. (I am assuming here that the SFN would not be for hybrid mode!)

As far as I can tell, DRM differs from IBOC primarily in that it occupies exactly the same channel space as the previous analog service. Meaning, there are modes for 4.5 or 5 KHz (SW channels), 9 or 10 KHz (LW and MW channels), as well as 20 KHz for better quality audio. But there's no really good provision for the supposed simultaneous transmission of digital and analog, in a hybrid mode, like IBOC. Whereas IBOC in the FM band doubles the channel to 400 KHz, and in the MW band it initially triples the channel to 30 KHz, in hybrid mode, then backs off to 10 or 20 KHz in all-digital mode. IBOC in the FM band stays at 400 KHz even after analog is shut off.

There is a suggested kludge for using DRM in a hybrid mode. Transmit the analog in VSB, and use the unused spectrum of the channel for the digital data. The thinking being that analog DSB radios will more or less work with this VSB signal, while the digital radios will get some small amount of room for maybe 20 Kb/s of data. Would be interesting to hear the noise created by this digital hash in the analog radios. And of course, no way will this work with an FM station, since the FM spectrum is not symmetric.

By contrast, IBOC uses the guard bands for the digital signal, when in hybrid mode. So how different is this, really?

Interesting thing is, Sangean is also playing in the DRM market. They are selling a portable DRM/analog radio.

http://www.sangean.nl/English/?opt1=News&opt2=DRM_RADIO&opt5=70

A few others are listed here, in their main web site:

http://www.drm.org/receiversequip/receiversequip.php

most of which appear to be USB receivers or computer cards. I didn't find any standard stereo components for DRM.

It looks to me like the digital radio landscape is very similar to DTV, but all happening with far less fanfare. I guess it should be possible to build all-standards digital radios too.

Bert

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