The digital radio future is here, and broadcasters need to be ready

October 1, 2002

The title is the basic premise of the recently completed Extreme Digital Road show, a joint informational and sales seminar co-presented in six major U.S. cities by Harris, Ibiquity Digital and Impulse Radio. I attended the presentation in Chicago. Present at the all-day sessions was a good representation of the engineering talent in the Chicago area and some management.

The day began with an informational, but mostly sales-oriented, presentation by Harris representatives on the history and current state of the art for the proposed IBOC digital standard. Emphasis was placed on the company's heavy commitment to the development of a system that will give the standard broadcaster the ability to compete with the parallel emerging technologies of satellite delivered digital radio. Another recurring theme was that this technology is not another high-tech means with no end, in the way that AM stereo and RBDS became. Presentations then followed by Ibiquity on the projected rollout of IBOC, and by Impulse radio on some exciting uses for the data bandwidth that is imbedded in the IBOC standard.

How do you convince broadcasters to spend, on average, a quarter of a million dollars per station on infrastructure changes for a digital standard that is not yet a standard, or a requirement?

It’s digital so it has to sound better, right?
Yes and no. A couple of clips were played to compare the digital reception and analog reception in a mobile environment. The digital signal at the sample points was free from the effects of multipath in the FM test, and in the AM test had superior audio fidelity compared to the 3.5kHz bandwidth of a typical auto receiver. There is no doubt that the digital signal makes the delivery of the product more robust. But what does the heavy digital compression (96kb/s) do to the product itself? Let’s just say that you wouldn’t want an audiophile to do a direct A-to-B comparison. This might be a real issue for some formats like classical, jazz or new age. On the other side of the coin, the popularity of the MP3 format, and the even lower bit-rate of the satellite delivered services, doesn’t seem to have been perceived by the bulk of the consumers as anything other than CD quality audio. Subjective listening tests have proven that most people cannot hear what the test equipment tells us is missing from the original source material.

Where are the receivers?
It’s the chicken and the egg relationship. The goal of the seminars is to get enough broadcasters in these six major U.S. markets to invest in the transmission side to provide 50 percent market saturation. Simultaneous rollout of the receivers at major retail outlets is expected to seed the market and develop consumer interest. Projected growth beyond the initial rollout is rapid.

What is the benefit to me as a broadcaster?
This is not the business of radio as usual. The digital IBOC signal contains not just the audio of the main product, but a significant data stream. Impulse Radio has developed a standards-based system to allow the broadcaster to use that data to sell more advertising product, something that will get the interest of station management. There is great potential to this aspect, and more information can be found at This technology gives the broadcaster the ability to market directly to the listener in a high-tech format he is already using on his cell phone, PDAs and on the Internet. The key is non-traditional revenue.

Another incentive to motivate the cost conscious broadcaster is the early-adopters incentive program. There is a license fee associated with the IBOC technology. That fee is based on a multiple of the annual FCC regulatory fee, and will average about $20,000. For a higher multiple, a 10-year payment option is available that will average about $3,7000/year. Royalty on the wireless data portion of the signal is waived until 2005. As an incentive, fees will be waived for life if a commitment is made to purchase the IBOC system before Dec. 31, 2002.

In the question and answer session that followed the morning presentations, several questions were raised.

What is projected target date for completion of AM nighttime studies? Due to the onset of winter propagation models, at least six months out.

What is the data rate for the ancillary data channels? From 115b/s–400b/s. The main channel is 96kb/s.

Will XM and other satellite-delivered systems be integrated into the final product? No, not at this time, but the receivers will be marketed as XM ready. The technical reason for this is that XM requires a different receiver front end. IBOC is seen as the base radio, and XM is seen as an accessory, much the same as a CD changer.

What are the possibilities of cross promotion and sharing resources to maximize data channel usage in a group-owned cluster of stations? This prompted a lengthy discussion of the possibilities of putting dual tuners in IBOC receivers so that a cluster could use the data channels in a soft key configuration to tune the second channel to data of another cluster station. This would allow one station to use their entire allocated data channel for weather, another for traffic, another for emergency services and yet another for direct marketing. The main tuner would stay on the audio of the desired station.

What type of audio processing is recommended for IBOC? Due to the heavy digital compression already in the transmission standard, it is recommended that less aggressive processing be used on the digital channel.

The afternoon session dealt with the technical side of IBOC. Impulse Radio presented the details of their interactive data stream standard, and Harris presented their product line and reviewed the three different ways a station can implement the technical facilities.

For the AM side, any of the modern digital transmitters should be able to pass the IBOC signal. Being that this was a Harris show, the focus was naturally on Harris transmitters, including the DX and DX Destiny series, as well as the soon-to-be-released DAX series of 5kW and under transmitters. An IBOC exciter is required, and that is used in a manner similar to AM stereo where the digital signal phase modulates the carrier, and the analog passes thru the regular audio stages. It should be noted that IBOC will not work on a plate-modulated transmitter or on progressive series modulation (PSM) designs. Single-phase 75kHz PDM transmitters will work with difficulty.

For FM, the IBOC transmitter must be capable of linear power amplification. This does not mean that a new transmitter is required in all cases. The Harris Z series of FM transmitter can be re-biased to operate in Class A or AB, and depending on the power level, the existing transmitter can pass the analog and the IBOC signals. There are two methods of transmitting the IBOC FM signal: combined amplification and separate amplification. Which to use depends on the station's power, available floor space and budget. In the combined amplification method, a single transmitter (or combined transmitters for high power) passes the analog and digital. In the separate amplification method, an external high power combiner is used to combine the existing analog transmitter and a new IBOC transmitter into a common transmission line and antenna. Due to the losses in the combiner, the analog transmitter must operate at 110 percent of the analog only power level, and the digital transmitter looses 90 percent of its power in the combiner and must be sized accordingly. The additional transmitter and combiner require floor space, and both systems will generate additional heat load for the HVAC and possibly require larger service from the power company.

A third method for FM discussed briefly, uses separate amplification and a separate transmission line and antennas. For this to work successfully it is necessary to have sufficient bay-to-bay isolation in the antenna, and it is best if the actual digital and analog elements are interleaved and matched. This is so the radiated signal maintains a consistent phase and amplitude relationship after leaving the antenna.

The question and answer session following the technical discussion was surprisingly brief. Here are some of the questions that were asked.

Has the system been tested successfully through a multistation combiner? Yes, using two different methods. Recently in Seattle, IBOC transmitters were injected into the existing Cougar Mountain combiner using circulators in place of the reject loads on each stations combiner module. The wideband port was then used to feed a separate transmission line and digital antenna.

Can a single IBOC exciter be used to drive two AM transmitters, for example a main and an aux? Yes, if both main and aux can pass the digital component. As an example, the Harris Dexstar IBOC exciter supports eight group delay setups that should accommodate the multitransmitter and multipattern configuration.

Is the data text display on the IBOC receivers capable of multiple languages? Not yet. It is currently the English subset of ASCII only. The European subset with accent letters is in the works.

What is the audio latency of the system? Six to seven seconds.

Overall, I was glad I attended the day’s sessions. Yes, it was clearly a sales pitch for IBOC, but the information gleaned was useful. Comments from other engineers afterward were mostly positive. There is still a real concern of the AM nighttime restrictions, and most were disappointed that the early-adopter incentive was of no value because budgets for 2003 are already done.

I fear that unless the FCC mandates the IBOC standard, or significant incentives are given to the broadcasters to invest in the technology, adoption will be much slower than anticipated. It will probably become reality because there is too much invested in the project thus far, but when is the question.

Wright is a senior studio engineer for Clear Channel Communications' Chicago Radio Group.