DRM/analog AM hybrid system being tested in Mexico City

[JasonW]

Hello All,

Although I do not wish to divulge my source at the moment, I have learned that an IBOC-type hybrid DRM (Digital Radio Mondiale)/analog system is currently being tested in Mexico City on the Medium Wave (AM) band.

They are broadcasting a 50 kW analog AM signal and a DRM signal that is 13 dB down from the analog signal from the same transmitter. They think that they can avoid the night-time skywave interference and adjacent channel interference problems of AM IBOC.

If the results are encouraging (and the party conducting the tests believes that they will be), they will next test this hydrid DRM/analog AM system in the US. This should be interesting. -- Jason

 

[Ai4i]

<a target="_blank" href=http://www.drm.org/>DRM</a> is the internationaly accepted standard for digital radio below thirty megahertz.
Might have been a good idea to check it out before all the HD stuff was sold!
I collect free paperweights!<P ID="signature">______________
Proud 2 B a pioneering satellite radio subs¢riber
Ai4i is always on the trailing edge of technology
______________</P>

 

[w9wi]

> They are broadcasting a 50 kW analog AM signal and a DRM
> signal that is 13 dB down from the analog signal from the
> same transmitter. They think that they can avoid the
> night-time skywave interference and adjacent channel
> interference problems of AM IBOC.

That's certainly an interesting experiment. A quick look at the DRM spectrum suggests it might indeed be a marked improvement over IBOC with regard to adjacent-channel interference.

However, I'm having a hard time seeing how the DRM won't trash the station's own analog signal! Looks to me like besides the broadband digital hash, there are three substantial pilot carriers that would beat with the analog carrier to create loud heterodyne tones in analog receivers.

I'd love to hear the results.

While the system may get a test in the U.S., I find it awfully hard to believe any on-channel system besides IBOC will ever receive serious consideration for commercial use in this country. Seems to me the choice-of-system decision has already been made.

 

[JasonW]

Continental Electronics is conducting these DRM/analog AM hybrid tests. They are one of the four companies (along with Nautel, Harris, and BE) that produce IBOC transmitters. Continental is very aware of IBOC's interference problems, which is why they're doing these DRM + analog tests. They'll publish the test results in a couple of months.

I agree that making digital and analog peacefully co-exist within the same channel allotment seems like a difficult proposition at best.

Maybe a "migration" strategy, similar to what was done when the AM extended band was opened up, would be better. In markets with open channels, let stations broadcast digital-only signals on new channels as well as analog on their existing channels. Since digital signals have a much better signal-to-noise ratio than analog signals, the digital-only transmissions could be much lower power to avoid interference. If and when the market penetration of digital radio receivers became high enough, they could turn off their analog signals and free up those channels for more digital stations. -- Jason

> > They are broadcasting a 50 kW analog AM signal and a DRM
> > signal that is 13 dB down from the analog signal from the
> > same transmitter. They think that they can avoid the
> > night-time skywave interference and adjacent channel
> > interference problems of AM IBOC.
>
> That's certainly an interesting experiment. A quick look at
> the DRM spectrum suggests it might indeed be a marked
> improvement over IBOC with regard to adjacent-channel
> interference.
>
> However, I'm having a hard time seeing how the DRM won't
> trash the station's own analog signal! Looks to me like
> besides the broadband digital hash, there are three
> substantial pilot carriers that would beat with the analog
> carrier to create loud heterodyne tones in analog receivers.
>
>
> I'd love to hear the results.
>
> While the system may get a test in the U.S., I find it
> awfully hard to believe any on-channel system besides IBOC
> will ever receive serious consideration for commercial use
> in this country. Seems to me the choice-of-system decision
> has already been made.
>

 

[dbdigital]

> DRM is the internationaly accepted standard for digital
> radio below thirty megahertz.
> Might have been a good idea to check it out before all the
> HD stuff was sold!
> I collect free paperweights!
>

I believe the FCC has already approved DRM for U.S. shortwave broadcasters.

Of course, they have little choice since the entire world has adopted it for SW.

But it's too bad the FCC won't approve DRM for AM as it could, possibly, have been a less expensive alternative to IBOC for small market broadcasters wanting to go digital. Even the DRM website suggests that the two systems could co-exist within a receiver for not that much more money.

db

 

[w9wi]

> Maybe a "migration" strategy, similar to what was done when
> the AM extended band was opened up, would be better. In
> markets with open channels, let stations broadcast
> digital-only signals on new channels as well as analog on
> their existing channels. Since digital signals have a much
> better signal-to-noise ratio than analog signals, the
> digital-only transmissions could be much lower power to
> avoid interference. If and when the market penetration of
> digital radio receivers became high enough, they could turn
> off their analog signals and free up those channels for more
> digital stations. -- Jason

Well, really there are no open channels on the AM band at night... Whether you protect a station's skywave coverage or not, the mere fact that it's broadcasting at night risks skywave interference to other stations, potentially within their groundwave protected contour.

Certainly, assigning a second channel for digital operation is the best idea. Television was lucky to have a large pile of "taboo" channels left over from the early days of UHF when tuners were, to put it politely, crap. That made it possible to assign everyone a second channel within the existing TV band, minimizing interference while avoiding the need to tread on other services' turf.

Radio isn't so lucky. Even on FM, in much of the country there is no place within the existing broadcast bands where second channels can be assigned. Arguably there are other places in the spectrum where digital radio could be put - certainly three of the channels being surrendered by TV would do the trick - but there hasn't been much industry interest in doing it that way.

 

[JasonW]

Continental seems confident that they can get the FCC's approval to at least test the hybrid DRM + analog AM on Medium Wave in the US.

Also, since iBiquity doesn't manufacture IBOC transmitters itself (BE, Continental, Harris, and Nautel do), if these transmitter manufacturers come to prefer the DRM/analog AM hybird system (if it works as hoped in the Mexico City tests) over IBOC, they may be in the driver's seat on this issue.

I couldn't blame them. DRM's codecs are open source, so radio stations would find DRM much less expensive to implement than the proprietary IBOC system, which would likely result in more DRM transmitter sales than IBOC transmitter sales. -- Jason

> I believe the FCC has already approved DRM for U.S.
> shortwave broadcasters.
>
> Of course, they have little choice since the entire world
> has adopted it for SW.
>
> But it's too bad the FCC won't approve DRM for AM as it
> could, possibly, have been a less expensive alternative to
> IBOC for small market broadcasters wanting to go digital.
> Even the DRM website suggests that the two systems could
> co-exist within a receiver for not that much more money.
>
> db
>

 

[JasonW]

I know what you mean--here in Fairbanks we have an unusual situation, just a handful of AM and FM stations and no AM skywave from elsewhere (except under unusual ionospheric conditions) because we're so far away from Anchorage. However, many larger communities don't enjoy that situation.

What services use the frequencies between 1700 kHz and 1800 kHz? If some channels in that slice of spectrum could be re-allocated for digital-only AM, that could be the place for interested stations to have their second channels. -- Jason

> > Maybe a "migration" strategy, similar to what was done
> when
> > the AM extended band was opened up, would be better. In
> > markets with open channels, let stations broadcast
> > digital-only signals on new channels as well as analog on
> > their existing channels. Since digital signals have a
> much
> > better signal-to-noise ratio than analog signals, the
> > digital-only transmissions could be much lower power to
> > avoid interference. If and when the market penetration of
>
> > digital radio receivers became high enough, they could
> turn
> > off their analog signals and free up those channels for
> more
> > digital stations. -- Jason
>
> Well, really there are no open channels on the AM band at
> night... Whether you protect a station's skywave coverage
> or not, the mere fact that it's broadcasting at night risks
> skywave interference to other stations, potentially within
> their groundwave protected contour.
>
> Certainly, assigning a second channel for digital operation
> is the best idea. Television was lucky to have a large pile
> of "taboo" channels left over from the early days of UHF
> when tuners were, to put it politely, crap. That made it
> possible to assign everyone a second channel within the
> existing TV band, minimizing interference while avoiding the
> need to tread on other services' turf.
>
> Radio isn't so lucky. Even on FM, in much of the country
> there is no place within the existing broadcast bands where
> second channels can be assigned. Arguably there are other
> places in the spectrum where digital radio could be put -
> certainly three of the channels being surrendered by TV
> would do the trick - but there hasn't been much industry
> interest in doing it that way.
>

 

[Ai4i]

I am confused.
DRM is described as open source (or is that DAB?), which I think means freely available to anyone who wants to incorporate it.
But it says <a target="_blank" href=http://www.drmrx.org/>here</a> that it is, "...built around fully licensed proprietary DRM encoding technology", which I think is like HD Radio.<P ID="signature">______________
Proud 2 B a pioneering satellite radio subs¢riber
Ai4i is always on the trailing edge of technology
______________</P>

 

[JasonW]

> I am confused.
> DRM is described as open source (or is that DAB?), which I
> think means freely available to anyone who wants to
> incorporate it.
> But it says here that it is, "...built around fully licensed
> proprietary DRM encoding technology", which I think is like
> HD Radio.

Hmm...I wonder if it's the DRM hardware that they're referring to, with the DRM software being open source like Linux? -- Jason

 

[w9wi]

> I know what you mean--here in Fairbanks we have an unusual
> situation, just a handful of AM and FM stations and no AM
> skywave from elsewhere (except under unusual ionospheric
> conditions) because we're so far away from Anchorage.

Yeah, Fairbanks is probably the best possible market for IBOC<grin>!

> What services use the frequencies between 1700 kHz and 1800
> kHz? If some channels in that slice of spectrum could be
> re-allocated for digital-only AM, that could be the place
> for interested stations to have their second channels. --

I don't know, but I do frequently hear digital signals in that range.

It doesn't seem to me there are enough channels there to accomodate a digital channel for everyone. (it is of course very dependent on just how many stations choose to implement digital; no matter what system is used, I can't imagine *every* AM station - or even 75% - going digital)

When I think of a second channel for digital radio, I think of UHF. (as used in most other countries) If the decision were to be made to allot second channels at UHF for digital, there is a superior technology ready and in use.

But again, it seems the digital radio decision has been made for the U.S., and I would be very surprised to see it changed anytime soon.

 

[JasonW]

> It doesn't seem to me there are enough channels there to
> accomodate a digital channel for everyone. (it is of course
> very dependent on just how many stations choose to implement
> digital; no matter what system is used, I can't imagine
> *every* AM station - or even 75% - going digital)

Agreed. Also, even the DRM folks are having problems getting affordable receivers produced. From the standpoint of power consumption alone, I just can't see a ubiquitous and affordable IBOC or HD equivalent of an analog AM pocket radio being practical for a long time, if ever. Even my Sangean DT-200V PLL-tuned analog pocket radio with a digital frequency display goes through AA batteries like a dog goes through Scooby Snacks. My analog "needle 'n dial" tuned pocket radios will play for 3 - 4 hours a day for months at a time before they need new batteries.

> When I think of a second channel for digital radio, I think
> of UHF. (as used in most other countries) If the decision
> were to be made to allot second channels at UHF for digital,
> there is a superior technology ready and in use.

I'm not that familiar with UHF TV channel allocations, but I see that newer TV sets only seem to have UHF channels 14 - 69 while older sets have 14 - 83. If channels 70 - 83 could be used for digital radio, there would be plenty of bandwidth since even an FM signal is "skinny" compared to the bandwidth occupied by a UHF TV signal. Digital-only IBOC could be used on UHF and would work very well there. -- Jason

 

[dbdigital]

> I am confused.
> DRM is described as open source (or is that DAB?), which I
> think means freely available to anyone who wants to
> incorporate it.
> But it says here that it is, "...built around fully licensed
> proprietary DRM encoding technology", which I think is like
> HD Radio.
>

As I understand it, licensing DRM simply involves a manufacturer joining the DRM Consortium for a modest fee (I think it's $5000.00). After that, the technology is fully available for them to use.

There are no fees to the broadcaster. Full details of the licensing agreement for manufacturers is on the DRM website.

db

 

[w9wi]

> Agreed. Also, even the DRM folks are having problems
> getting affordable receivers produced.

I think that's the biggest thorn in the side of HD Radio. It's difficult to see an effective "entrance strategy" that'll get competitively-priced receivers into the public's hands and provide enough reliable HD service to convince them to buy.

> I'm not that familiar with UHF TV channel allocations, but I
> see that newer TV sets only seem to have UHF channels 14 -
> 69 while older sets have 14 - 83. If channels 70 - 83 could
> be used for digital radio, there would be plenty of
> bandwidth since even an FM signal is "skinny" compared to
> the bandwidth occupied by a UHF TV signal. Digital-only
> IBOC could be used on UHF and would work very well there.

Channels 70-83 were reassigned years ago. They're used largely for cell phones and public-service two-way radio, among other things. It's too late to claim that spectrum for audio broadcasting.

However, channels 52-69 are going away in three years. Two of these channels have already been set aside for public-safety use, and much of the rest is already being apportioned. Ironically, at least one channel is apparently to be used for... digital audio broadcasting. On a subscription basis.

Three of these channels would accomodate 90% of existing FM stations in existing *analog* mode. They'd support far more programs in any digital mode, either the Ibiquity standard or Eureka.

 

[JasonW]

> > Agreed. Also, even the DRM folks are having problems
> > getting affordable receivers produced.
>
> I think that's the biggest thorn in the side of HD Radio.
> It's difficult to see an effective "entrance strategy"
> that'll get competitively-priced receivers into the public's
> hands and provide enough reliable HD service to convince
> them to buy.

Yes--digital vs. analog radio isn't like the difference between color television and black-and-white television, where color was an obvious and long-anticipated improvement. My local AM and FM stations sound superb, especially on my high-quality receivers (Sangean DT-200V and Lennox "Sports Radio"). The audio processing on the stations' ends is so good (except for a few slightly "muddy" USA Radio Network feeds on KFAR 660) that I doubt that IBOC would sound better enough for the difference to be very noticeable.

> Channels 70-83 were reassigned years ago. They're used
> largely for cell phones and public-service two-way radio,
> among other things. It's too late to claim that spectrum
> for audio broadcasting.
>
> However, channels 52-69 are going away in three years. Two
> of these channels have already been set aside for
> public-safety use, and much of the rest is already being
> apportioned. Ironically, at least one channel is apparently
> to be used for... digital audio broadcasting. On a
> subscription basis.
>
> Three of these channels would accomodate 90% of existing FM
> stations in existing *analog* mode. They'd support far more
> programs in any digital mode, either the Ibiquity standard
> or Eureka.

With that being the case, it sounds like it still might not be too late to snag two or three UHF channels for non-subscription, free digital radio. Maybe the DRM Consortium could put together a successful bid for the channels. -- Jason

 

[w9wi]

> Yes--digital vs. analog radio isn't like the difference
> between color television and black-and-white television,
> where color was an obvious and long-anticipated improvement.

Well, too, remember that it took a LONG time for color TV to become the norm. The first color set came out in 1954 but as late as the mid-1970s it was not unusual to find a home that had only B&W TVs, and well into the 1980s many homes had a number of B&W "second sets". If a similar uptake period were to occur for HD radio, we won't see the analog shut down until about 2030.

(of course, a TV is considerably more expensive than a radio, one might expect uptake of HD radio to be less inhibited by price if they can get the price *ratio* down to what it was for TV. On the other hand, most households have a lot more radios to replace than they have TVs.)

> My local AM and FM stations sound superb, especially on my
> high-quality receivers (Sangean DT-200V and Lennox "Sports
> Radio"). The audio processing on the stations' ends is so
> good (except for a few slightly "muddy" USA Radio Network
> feeds on KFAR 660) that I doubt that IBOC would sound better
> enough for the difference to be very noticeable.

At least on my set, I find it hard (impossible!) to find any difference in audio quality between analog and HD on FM. On AM, HD sounds *different* but I wouldn't say *better*. It sounds like a frequency-response difference which could be receiver-induced. (since I only have one AM HD station to work with) The AM HD does appear to have some audible compression artifacts. (I wouldn't consider them annoying but they are noticable) The analog signal must be VERY strong (and thus free of interference/noise) before HD works.

> With that being the case, it sounds like it still might not
> be too late to snag two or three UHF channels for
> non-subscription, free digital radio. Maybe the DRM
> Consortium could put together a successful bid for the
> channels. -- Jason

I don't think the DRM Consortium has anywhere near enough money.

Any such decision would have to be one of the government agreeing to assign the spectrum to broadcasting without significant charge. I don't think the industry can afford to buy it at auction. (this is of course another reason why it won't happen)

If this spectrum *were*, for some reason, to become available, I don't think DRM would be the way to go. While I understand it has been tested at VHF, it's really designed to work in the restricted bandwidth of the HF and medium-wave/long-wave spectrums. When *extreme* conservation of bandwidth is not necessary, Eureka becomes a better choice. (among many reasons, because Eureka equipment is already widely available)

 

[mikl73]

> > I am confused.
> > DRM is described as open source (or is that DAB?), which I
>
> > think means freely available to anyone who wants to
> > incorporate it.
> > But it says here that it is, "...built around fully
> licensed
> > proprietary DRM encoding technology", which I think is
> like
> > HD Radio.
>
> Hmm...I wonder if it's the DRM hardware that they're
> referring to, with the DRM software being open source like
> Linux? -- Jason
>

you beat me i was about to say just that....

think of iboc as windows/microshaft...big fees and licensing
DRM is the Linux open source community.... much cheaper to get on the playground