Frequently Asked Questions

Although IBOC DAB will give over-the-air broadcasters a way to compete digitally with new listener-encroaching services, technically it's a whole new ballgame. This is why Harris is introducing end-to-end Extreme Digital radio solutions - to ease your transition to digital. These standard-setting, future-proof solutions include source, studio, STL and IBOC transmission products as well as systems experts who can help you determine your smoothest and most cost-effective migration path.

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1. Why is IBOC better than analog?
There are three reasons:

  1. IBOC's improved sound (AM=FM stereo; FM=CD) will enable over-the-air radio to compete with alternate delivery services.
  2. IBOC can actually increase the number of listeners because it eliminates FM multipath and virtually eliminates AM noise and fading.
  3. IBOC will establish the foundation for new revenue-producing data services.

2. How will IBOC transmission be implemented?
Radio stations will broadcast their current analog signal and their new IBOC signal over their existing channel.

AM stations will use the same transmitter for AM and IBOC. The IBOC exciter will be connected to the external RF input port and audio input port (like AM stereo is connected now). FM stations will have two main options:

  1. Separate amplification, using an analog FM transmitter and an IBOC digital transmitter, and then combining the output at high level.
  2. Common amplification, using a new solid-state FM+IBOC transmitter to amplify both signals.
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3. Will I be able to use my existing transmitter?
This depends on your existing transmitter, and you'll want to talk to the manufacturer. However, here are some very general guidelines.

  • AM: If you have a Harris DX or 3DX transmitter, you should be able to implement IBOC by adding an exciter and making very few or no modifications. Other solid-state transmitters may require modifications ranging from minor to major. And tube-type transmitters probably will not be upgradeable.

  • FM: If you'll be using separate amplification, you should be able to use your current FM transmitter for the analog signal. Keep in mind that your analog transmitter will require approximately 10% more average power for high-level combining. To implement IBOC, you'll purchase an IBOC transmitter and a high-level combiner when you are ready.
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4. Will I be able to convert my analog FM transmitter to IBOC operation?
Probably not. Although it may be technically feasible to convert some late-model, solid-state FM transmitters, once the transmitter is converted it no longer will be able to make its original rated power. (An IBOC-only transmitter used in separate amplification will be rated at about 1/10 the power of the FM transmitter as a result of combining losses.) As a result, unless you've purchased an FM transmitter with sufficient headroom, conversion will probably not be practical.

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5. How is the IBOC signal different from the FM signal?
The IBOC signal includes an amplitude component in the RF waveform that requires linear amplification. This means that during the transmission process, the IBOC transmitter must preserve the original signal's amplitude and phase adding nothing to it (i.e., distortions) and subtracting nothing from it, from input through amplification through output. Signal linearity is essential for two reasons: first, to maintain coverage, and second, to ensure compliance with the FCC's RF spectral mask to prevent interference.

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6. What does it take to ensure signal linearity?
To ensure linearity, IBOC transmitters employ some level of pre-correction or filtering to overcome distortion products created by non-linearities in the system. Well-implemented pre-correction offers four major advantages:

  1. it ensures the transmitted signal stays within the required RF spectral mask.
  2. It can lower the bit error rate, resulting in improved signal coverage.
  3. It can maximize power output. In other words, it will enable you to push your transmitter harder for more power per amplifier.
  4. Lower intermodulation distortion provided by effective pre-correction may actually eliminate the need for external bandpass filters or, if a filter is needed, result in a simpler and lower-cost filter.

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7. I need to replace an analog transmitter now but I'm not ready for IBOC. What should I do?

  • AM: Look for a transmitter that has been tested with an IBOC exciter and has a track record. You'll need a solid-state transmitter that has enough bandwidth to pass the IBOC signal without attenuation or corruption — ideally, 50kHz or more. You'll also need to ensure that input ports are available for the IBOC exciter.

  • FM: If you plan separate amplification (high-level combining), any existing analog transmitter will probably be acceptable provided you can get 10% more TPO from it to cover combiner losses. However, if your FM transmitter power is 7kW or less, buying a new common amplification transmitter may be your most cost-effective choice. With a common amplification transmitter, you can broadcast only the analog signal now and then upgrade to IBOC with the addition of an IBOC exciter later.

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8. Will I need a new antenna?
Again, you will need to evaluate your specific situation. General guidelines follow.

  • AM: Non-directional stations with an ACU that has been designed using modern computer-aided modeling should be okay. However, if the ACU is old or was hacked in by methods of days gone by, a sweep to examine bandwidth is recommended. AM IBOC occupies 30kHz bandwidth, so the antenna system should perform beyond this absolute minimum. Broadbanding circuits, symmetry-enhancing circuits and phase shifters may improve the performance of any AM antenna system relatively inexpensively. These same circuits may be used at the common point of directional arrays as well. Also, in directional AMs, a sweep of the common point will give you an idea of your symmetry and bandwidth. This is important because IBOC requires a symmetrical load.

  • FM: Since most FM antennas have at least 400kHz bandwidth, it should be possible to use existing antennas. However, it may be a good idea to check the antenna's specification to ensure you have sufficient bandwidth.

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9. What do I need to consider beyond transmission equipment?
You'll need a second audio processor especially designed for IBOC audio and both the analog and the IBOC audio processors will have to be located at the transmitter site. Audio will be delayed in both signals, so you won't be able to monitor the IBOC signal off air. For this reason, you might want to install an off-the-board audio processor that allows the DJ to hear a processed audio signal rather than the signal straight from the console.

Beyond audio processing, you should examine your air chain for weak points. Some questions to ask: Is my STL digital? Is my main audio processor digital or analog? Is my audio console digital? Am I using any other source audio compression algorithms in my air chain? What about my automation system? Is my system compatible with the PAC source compression algorithm that IBOC uses? And, what IBOC monitoring and test equipment will I have to purchase?

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10. I'm feeling overwhelmed by all I need to learn about IBOC. Who can help?
Harris would like to be your IBOC information source. We have worked with the teams who have brought you IBOC from its earliest Project Acorn days. We have the knowledge and the people to help you make a smooth transition at every point in your air chain. We have digital automation and studio experts, digital STL and transport experts, and RF transmission experts who share their knowledge with our highly trained sales staff.

We also understand that there is no single approach to IBOC that will work for every situation. You'll want to determine the best options for your operation both technically and economically. When you are ready to get started, please give us a call.

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1. When will broadcasters hear the new AM HD-Radio codec on air?

The new HDC codec has been released. Harris began shipping Dexstar units with HDC in September, and will distribute software code to HDC customers this month (October 2003).

2. When can customers expect to see HD radios for sale?

A limited run of consumer aftermarket receivers will be available after November 1, 2003. Widespread retail distribution of HDC capable receivers should begin after the January 2004 CES show.

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3. Where can customers find more information about NeuStar?

Harris introduced the NeuStar digital audio conditioner at NAB 2003, where it was honored in the "Pick Hit" competition. Updated information on the NeuStar can be found on the Harris HD radio website.

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4. What are the audio sample rate problems with STL, 32kHz vs. 44.1 kHz?

Sticking with 44.1 is ideal because that is the sampling rate of the IBOC system. However, the use of 32 kHz sampling on the STL will likely be imperceptible. The upper frequency limit to a 32 kHz system is 15 kHz, while it is 20 kHz for a 44.1 system. Ask yourself if this difference will be audible to your listener, using a codec that masks inaudible information anyway. The input to the IBOC system has a rate converter that can easily handle the 32 kHz.

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5. Will IBOC in the future be able to provide mobile video services such as in the Eureka 147 standard?

With the present generation of low bit rate video codecs, it is certainly feasible that one could implement limited frame rate video in the extended hybrid and the proposed all-digital HD Radio modes. The actual implementation of this type application would need to be driven by market demand as are any of the advanced application services (AAS).

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6. What is the time line anticipated for 5.1 in FM and is there a timeline for receiver firmware?

Kenwood has stated they plan to implement 5.1 for FM HD Radio in their calendar 2005 model radios.

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7. Where can 3rd party developers get the most recent SDK for developing applications for Program Associated Data?

The contact for this would be Jeff Detweiler, iBiquity Digital Corp., detweiler@ibiquity.com, 908-580-7024.

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8. What can be done about the interference that HD radio causes to adjacent AM channels?

There are four classifications of potential interference: ground wave to ground wave, ground wave to sky wave, sky wave to ground wave, and sky wave to sky wave. A sampling of voiced concerns about potential interference (i.e. letters to Radio World, NAB sessions on the subject, and Internet list servers) shows that many are concerned with maintaining the ability to hear stations at a location other than the primary service area. It is likely (but by no means guaranteed) that the FCC will be most concerned with the potential for interference in the station's PRIMARY (ground wave) service area, and less so with new interference in the secondary and intermittent service areas.

In this regard, existing protection ratios required for first and second adjacent ground wave signal should afford adequate protection in the primary service area. That would leave only sky wave to ground wave as an issue requiring some in- depth examination. Hopefully when the iBiquity study is released, it will shed some light on all four of these interference scenarios. Ultimately, the broadcasters will need to decide whether the benefits offered by IBOC do or do not outweigh the occasional loss of service in their secondary and intermittent service areas.

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9. How would you recommend that an LPFM station incorporate IBOC inexpensively?

As with any potential investment, the LPFM operator needs to monitor the technology's benefits over the next several years within the context of his business plan and revenue potential. As the technology and the applications mature, lower-cost, integrated solutions engineered for low power applications will become available.

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10. Will IBOC be interconnected with a satellite system for coast-to-coast access to a local radio station?

Not to be confused with Digital Audio Radio Service (DARS), HD Radio is a terrestrial digital broadcast system. While many stations receive content from a single distribution source (i.e. network feeds or global network simulcast) few have tried to offer contiguous service from coast to coast. HD Radio preserves the coverage of existing stations and the concept of localism that is essential element of AM/FM broadcasting.

At this time there are no active plans to interconnect satellite and terrestrial HD Radio broadcast systems. However, there are currently a couple of stations simulcasting their programming on Sirius. This trend will likely continue for large market stations and implementing HD Radio will offer an opportunity to efficiently transport a station's programming to a satellite provider like Sirius due to the low bandwidth requirement of the HD Radio audio stream.

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11. In an all digital system, how does Harris propose we insert EAS signals and where?

The HD Radio system all digital specification calls for EAS type functionality in the advanced application services. In the HD Radio hybrid mode, the EAS tone/audio source would need to be inserted ahead of the first conversion to an AES audio stream. When the system converts to an All-Digital mode there will need to be a small segment of the data bandwidth reserved for EAS or some equivalent emergency alert system. This should not be a problem even for AM given the small amount of data required to transmit the emergency codes, warning signals and text. There should also be opportunities to implement other systems such as Amber Alert, traffic codes, weather alerts, etc. This type of data would be injected into a data port of the HD Radio exciter or a data port on some other data management hardware. The exciter or other hardware will then multiplex all data sources (including program audio) together and then modulated onto the RF carriers.
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12. How will digital transmissions affect internet webstreaming? What additional equipment will be required for smooth transitioning and quality transmission?

These are really two different systems and one is not affected or limited by the other. At this time it is not possible to use the HD Radio codec for streaming audio therefore two different codecs would be required. The most important thing to do, as you move forward with equipment purchases, is to move toward transporting and working with linear digital audio within the studio plant and within any STL transport system. The idea is to avoid subjecting the audio to any data bit reduction (digital compression) schemes as the IBOC codec and any streaming audio codec will be doing that and you do not want to cascade compression algorithms as this will quickly degrade audio quality.

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13. Will a spectrum analyzer be required for proper monitoring of the HD plant? As this is a high ticket item, and since the mask of the transmitter output is set by its design, is this REALLY a necessary item?

A spectrum analyzer is required for setup of an AM IBOC system. It is not a requirement for ongoing monitoring; however, in order to ensure compliance with the FCC's RF mask on at least an annual basis, access to one is recommended. It should be pointed out that if a station uses the manufacturer's installation services, they should provide the necessary test equipment to install and initially test the system, relieving the station of the need to own one.

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14. When more AM stations with HD come on the air and first adjacent stations to them receive interference in their fringe listening areas and then complain to the FCC, how likely is it that the FCC will "force" the HD station to cut back on their digital carrier levels or even completely shut off HD?

It's likely that the FCC is primarily going to be concerned with protecting the station's PRIMARY service area, as opposed to it's secondary or intermittent service area (what you refer to as "fringe"). Stations impacted in the PRIMARY service area are those likely to be afforded protection by FCC requirements that interferers reduce their digital carrier levels. Depending on the class of service, this is at the 2 mV contour, less for Class A stations. If broadcasters as a group believe that secondary and intermittent service areas cannot be compromised, then they are essentially saying that they do not believe the benefits offered by IBOC operation outweigh the loss of service in those areas. Broadcasters need to provide some hard data to the standard setting group (NRSC) as to the percentage of listeners or revenue in their PRIMARY vs. secondary or intermittent service areas. Then they need to weigh that against future growth potential with a digital signal.

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15. Where can I find the ePal block diagrams?

You can download a PDF version of these block diagrams from the Harris HD Radio website. Download the ePAL application note.
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16. Any guess as to when FCC will rule on separate or interleaved antenna would be approved or rejected?

The FCC is likely to seriously consider the recommendations of the NAB if they find that their study is based on sound field data. Since there are really no adopted FCC standards yet for any IBOC operation (it's all STA), the formal adoption is likely to come when the full rules are adopted, likely in 2004.

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17. About a third of my (FM) station`s listenership is via an on-channel Booster station. What are the HD Radio issues with synchronous on-channel Boosters?

Single Frequency Network (SFN) is possible with iBiquity's HD radio technology. However, SFN will likely require additional design and test work by iBiquity and Harris in a next generation platform to make possible consistent frame alignment upon system restart. Although untested at this date, we know of no fundamental reasons why an SFN couldn't be deployed once the proper design and field testing is implemented.

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18. Can a single exciter feed more than one AM transmitter such as a BU TRX?

Presumably this question means not feeding them simultaneously, but rather the ability to "hot switch" the exciter from one tx to another. In theory, there is no technical reason why this special implementation couldn't be done; soon-to-be released software code for the exciter will support loading multiple configurations, even remotely. The issue is that each transmitter has its own phase/magnitude group delay which must be loaded at the time the transmitters are switched. However, before manufacturers can provide guidance on the tactical way to implement this, some prototyping and field testing will be required. We expect this to become an important issue if and when nighttime AM IBOC is authorized, because dual day/night transmitters are common.

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19. Where can I get more information about the HDV audio coding?

Information on HDV can be found at several web sites related to HDTV HD recording. The HDV format specifies the data recording of MPEG2 inter-frame compressed high-definition video signals at either 19 Mbps or 25 Mbps. HDV is proposal of basic specifications for a format which realizes recording and playback of high-definition video on a DV cassette tape. The HDV format includes 720p (progressive) and 1080i (interlace) specifications and is not related to audio coding.

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20. Is there an active serial port on the IBOC exciter available for inputting Program Associated Data?

Yes, the Harris Dexstar exciter has two USB ports, two RS232 ports, and one Ethernet port. The iBiquity application continuously scans these ports looking for the PAD data and will lock to a valid signal.

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21. Will FM SCA's (67 & 91 kHz) be protected with the addition of the HD Radio carrier? Will it be possible to continue the SCA signal when the analog carrier is eliminated?

Both the 67 kHz and 92 kHz FM SCAs are protected and can continue to operate when the system is operating in the primary carrier mode (digital carriers start at about +/- 129kHz). There is a slight (2 dB) degradation in the signal to noise ratio of the 92 kHz subcarrier. However, this has proven not to be a problem and several stations running 92 kHz subcarriers and IBOC have not had interference problems with their 67 or 92 kHz SCA channels. It will not be possible to transmit the analog subcarriers in all- digital mode. When HD Radio goes all digital, the functionality of the SCAs will have also been converted to all digital, by that time.

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