Apr 1, 2003 12:00 PM
Thoughts on DRM and HD Radio
We have entered the era of digital radio broadcasting, and engineers will face many daunting but interesting challenges as HD Radio is rolled out, especially on the medium-wave side. There are several obvious issues, which include antenna bandwidth, nighttime operation and the somewhat less obvious issue of protecting the digital signals that are not systematically protected on the adjacent channels.
The timing is right to consider if there are other methods that would give broadcasters additional tools for their conversion to digital.
AM or medium-wave broadcasting has always been an extremely important and powerful broadcast medium. It is a universal technology available worldwide. Surely that point was a big factor for USA Digital Radio when, on Jan. 24, 2000, the company agreed to work with the Digital Radio Mondiale (DRM) consortium to develop a universal, world standard for digital radio. Because no production-line receivers for digital radio exist at this time, it is difficult to determine the true compatibility of these two systems. Both are part of the ITU digital broadcast specification BS 1514-1. HD Radio is referred to as �double sideband IBOC.� Technically, the two systems utilize OFDM modulation techniques with some form of QUAM modulation. Until recently, both used AAC audio coding; Ibiquity now uses the PAC algorithm. Other than the requirement to license two audio coding algorithms, building a universal receiver for use anywhere in the world should not be an issue.
The point is that there is no good reason why American broadcasters should not have the ability to use either of the two digital methods described in the single ITU 1514-1 specification. This would not be a �marketplace decision� as it was with AM stereo, primarily because there has already been effort put into making the two systems part of one standard. DRM is has already been authorized by the FCC for use (at least experimental) on the short-wave bands.
DRM is the International standard for digital radio below 30MHz according IEC specification 62272-1. It is non-proprietary and license-free. DRM offers scalable bandwidth, varying degrees of ruggedness vs. quality and is optimized to deal with sky-wave transmission. DRM also permits multiple programs (up to four) as opposed to HD Radio, which offers a single channel. DRM can support synchronous transmission so that a network of low-power boosters could replace large transmitter sites. There are DRM synchronous systems now in operation.
Ignoring the additional features of DRM, why muddy the waters now? Some good reasons are that a DRM approach could easily solve the night operation issue and be more compatible to narrow-band antennas. DRM can operate in a bandwidth as small as 4.5kHz or be expanded to carry more data and programs to a full 20kHz wide channel. This possibility plus the ability to choose one of two different levels of QUAM and from one of three audio compression schemes make it possible to optimize the signal from a very FM-like stereo signal to one optimized for speech and possibly very poor propagation or for multiple programs. This is not a one-time choice, but something that could be changed according to day part. Similar to the HD Radio approach, DRM can fall back to analog, but unlike HD Radio it sends a flag that can use any AM or FM frequency as analog backup. An alternate frequency flag can send receivers to another digital channel as well.
Because of the scalability of the DRM technology it can fit into our crowded broadcast spectrum and remain relatively protected as well. The best way for a station to accomplish this would be to convert the analog operation from dual sideband (DSB) operation to vestigial sideband (VSB) operation. One sideband would carry a full-bandwidth 10kHz analog signal while the other sideband would carry a 2kHz analog signal, leaving 8kHz for the digital signal. This would fit entirely within the existing NRSC channel. More bandwidth would be possible if overlap into the second-adjacent channel was allowed, as is the case with HD Radio operation. In many cases, a wide-band day mode and narrow-band night mode could be used. Not only would this solve night operation issues but also it would be accomplished in almost one-quarter of the bandwidth that we are now contemplating.
If the FCC were to slightly broaden its initial ruling and permit digital broadcasting in accordance with ITU BS 1514-1, broadcasters would have another valuable tool for the transition to digital, at least on the medium-wave band. Those who feel they can best benefit from HD Radio can also continue to perfect that component of the specification. It is very important that as we move forward that the medium-wave band remains a universal medium worldwide.
New York, NY
Dear John Battison:
I enjoyed your [RF Engineering, January 2003] article. It brought back memories of my early ham radio days. Back in 1947, I bought a two-meter transceiver kit from Allied Radio. This transceiver used a 6N4 tube as a super reg. receiver and used the same tube as a modulated oscillator/power amp on two meters. The audio section relied on a 7C5.
Because I lived on a farm in Northeastern Montana, and I was afraid of causing interference to another station � even though our closest neighbor was 2.5 miles away � I built a lecher wire system to measure my transmitter frequency. I later replaced the lecher with a Murdo Silver absorbtion frequency meter.
The lecher system is almost a forgotten art. Your article reminded me that there are many practices that at one time were common knowledge, but have faded from current memory. For example, I recently had an experience where I needed to install an inverse feedback ladder in our vintage 10kW AM broadcast transmitter. I had to dig through several resources until I found a reference that I could apply.
John, I would love to see an article written by you about setting up feedback ladders. I went through my library at home and found only two books that gave information on feedback ladders for inverse feedback systems. One was my college text book called Principles Of Radio by Henry and Richardson from 1947. The other book, also from 1947, is called The Eleventh Radio Handbook.
It seems to me that information on the feedback ladder's design is about as far gone as the use of KC for kilocycle and MC for megacycles. John, are we really that old?
Dale Heidner, W7NAV
KGVW and KCMM
I was reading an article about the waiver signed by Artemus Records and the RIAA. We launched an Internet radio station playing independent country music artists and only play those that we have waivers from. Radionashville.us is new and offering air-play for the artists who can't receive radio play anymore and unknown artist's who need a chance to be heard. It has been a lot of work and no profit.
We are getting waivers from every artist or label that we play on this site. It is the only way we can stay in business. As of now, we have a few waivers from larger labels and many from small independent labels. I hope that some day the major labels will be calling us instead of us calling them.
It only makes sense that record labels would want their artist's music to be played and have as much exposure as possible. Even though we are a new Internet radio station, we expect thousands of listeners a week. We also offer an online store to sell the product of the artists who can't get shelf space anymore. I feel that this is the future of the music business. Also, we are going to make CDs available for download for a minimal fee.
If more labels would look at every site as being a potential store, then album sales would increase and the industry would not be having so many problems. Also, the major distribution companies will need to drop-ship individual CDs and set up a policy for doing this with Internet stores.
Harry Martin's coverage of the latest SESAC rip-off [FCC Update, February 2003] was well written as usual, and it brings out yet another case of legalized plunder to the detriment of broadcasters.
SESAC, in my opinion, suffers from a major inferiority complex, derived from its unwanted repertoire of music that most stations would gladly never play if they could, but strangely, SESAC would never supply a list of its material to stations, so that stations could avoid the expense of the SESAC license.
Now, under �super-gouge� court rulings, SESAC becomes the latest case of bandits without pistols wherein broadcasters are left with no options other than taking the SESAC license. What's wrong with this picture?
To me it's wholly un-American and extremely questionable as to the merits of our illustrious legal system; the same system that brought you the O.J. Simpson debacle.
William S. Cook
Beware of digital media
It is unfortunate that television and radio stations have not yet banded together to demand their share of the proceeds of the billions of promotional value that broadcasters have given to Hollywood over the many years. I am glad to see and read someone speak out against the greed and avarice of the performers and producers.
When are broadcasters going to unite and take a stand? Or do we think that problems are just going to go away, or perhaps someone else is going to take care of them for us?
For instance, consider the horrible Internet royalties and burdensome reporting requirements that the composers, authors, publishers, performers and record companies have skillfully thrust upon every radio station desiring to better serve their listeners on the Internet.
In our case at WCPE, the Internet royalty rates are 255 times higher per-capita than those for our public radio audience. I have been fighting for our Internet listeners for two years now, trying to seek fair and reasonable royalty terms. I've gotten to know a number of the players face-to-face, and I assure you, there are big problems hiding ahead.
Both commercial and non-commercial broadcasters are still dozing off at the wheel when it comes to the consequences of the Digital Millennium Copyright Act (DMCA) and the fees and provisions that the recording industry and their friends skillfully and quietly lobbied to create this law.
Broadcasters may think that they are clear for the most part, but I venture to say that if broadcasters don't fight this monster now at the �Internet� level, there will be real trouble.
After digital AM and FM broadcasting takes hold and the audience expects a digital signal from their favorite local station, one small modification to the DMCA (likely to be hidden and attached to some benign bill) will open Pandora's box. The record industry � angry for all these years about not being able to collect the performance royalties that they feel �cheated out of� from broadcasters � will have their day and their way.
Take a good look at the DMCA and the statutory license requirements and notice that only a few words prevent these harsh terms from being thrust upon terrestrial digital broadcasting.
The special interest groups that lobbied for the DMCA will have their efforts rewarded when radio stations have to pay an �ephemeral royalty fee� for the RAM copy of performances in the buffer of our digital STL receivers � not to mention our digital transmitters and every single digital receiver tuned to them.
After all, it is called the Digital Millennium Copyright Act, and we are talking about the future of digital broadcasting.
Back in the sixties, many broadcasters donated their little 3,000W FM stations to their local college; they didn't see a future in FM broadcasting. Let's not repeat that same mistake by ignoring the DMCA and the future of Internet broadcasting.
Deborah S. Proctor
Wake Forest, NC
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