October 5, 2009
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Increasing FM IBOC Digital Power – the Manufacturer’s Perspective

One of the highlights of the engineering program at this year’s NAB Radio Show (Philadelphia, September 23-25, 2009, www.nabradioshow.com) was a session entitled “The IBOC Power Issue – You Have Questions, We Have Answers!” This two-hour long panel discussion, moderated by Milford Smith, vice president of Engineering for Greater Media (and chairman of the National Radio Systems Committee, NRSC), included presentations from iBiquity, NPR Labs, the four principal U.S. HD Radio transmitter manufacturers (BE, Continental, Harris and Nautel) and the FCC. While the iBiquity and NPR Labs' presentations focused on performance and compatibility issues, and the FCC’s comments focused on regulatory policy, the manufacturers talked about some interesting market and equipment issues that are summarized here.

Tim Bealor, vice president, RF Products for Broadcast Electronics (BE) and Mike Troje, sales manager Continental Electronics, were the first two manufacturers’ representatives to speak and they focused on how the possibility of higher power FM in-band/on-channel (IBOC) digital sideband operation is impacting the marketplace. Their separate presentations arrived at similar conclusions, namely, that the uncertainty about whether a power increase will be authorized (and if so, how much) is making it difficult for broadcasters to move forward with new HD Radio installations.

Mr. Bealor noted that to-date only about 20 percent of radio broadcasters overall have implemented HD Radio technology and characterized those who have yet to convert as belonging to one of the following groups:

  • Mid-market groups
  • Smaller stations of major groups
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  • Small-market groups
  • Smaller groups in major markets
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  • Smaller public stations
  • Translators
    		•
  • Boosters
  • Individual stations
    		•
  • Small ownership stations
    •      		 









    He said that broadcasters not yet ready to build digital facilities are looking for cost effective analog solutions now, that can be converted to -20 dB HD Radio operation (i.e., the currently authorized power level), then be upgraded to -10 dB or -14 dB HD Radio power levels (i.e., the increased power levels being contemplated) at some point in the future.

    Mr. Troje provided some additional HD Radio transition statistics, showing that about 17 percent of non-commercial and 21 percent of commercial broadcasters have already made the transition to HD Radio facilities. He highlighted three specific needs of broadcasters who have not yet made the transition:

  • Action from the FCC on allowable higher level FM IBOC power levels – he believes these broadcasters “...need to see an ‘end game’ before they can be expected to get on-board;”
    		•
  • A realizable business model for small to medium markets;
    		•
  • More automotive and portable receivers.
    		•

    The final two manufacturer presentations were from Geoffrey Mendenhall, vice president - Ttransmission Research and Technology, Harris Corporation, and Gary Liebisch, regional sales manager, Nautel, Inc. These two presentations focused more on the technical challenges surrounding the increase in FM IBOC sideband power level. Among other things, Mr. Mendenhall summarized the linearity challenges faced by manufacturers in building transmission equipment to operate at the higher IBOC sideband power levels:

  • Due to the higher peak-to-average AM component of the increased IBOC carrier injection, a common amplification transmitter must be further de-rated from class ”C” saturated FM operation;
    		•
  • The more the amplitude of the IBOC carriers is increased, the more common amplification transmitters must be de-rated;
    		•
  • For HD-only, separate amplification without the linearizing effect of the constant envelope analog FM signal, the maximum available total power output (TPO) must be further reduced to improve intermodulation distortion (IMD) suppression;
    		•
  • At -10 dBc (10 percent) injection, the RF IMD products need to be suppressed an additional 10 dB at the same time the power output is increased by 10 dB. This represents a 20 dB linearity improvement from that needed at -20 dBc (1 percent) to maintain the original RF mask compliance.
    		•

    In the Nautel presentation, Mr. Liebisch explained that Nautel has typically used a “rule of thumb” value of 40 percent to estimate the output power available from a Nautel transmitter at the proposed -10 dBc power level so that, for example, Nautel would “de-rate” a 40 kW transmitter to 16 kW for the higher IBOC power level using this rule. Mr. Liebisch said that recent testing has confirmed the 40 percent value for transmit frequencies in the non-commercial educational (NCE) portion of the FM band (88 to 92 MHz) but interestingly, in the commercial portion of the band (92 to 108 MHz), the available power is consistently higher (see graph at right). Consequently, for the 40 kW example at -10 dBc, 20 kW was the available power for the commercial band while only 16 kW (corresponding to the 40 percent rule) was available for the NCE band. Mr. Liebisch indicated that Nautel is working to improve the NCE performance and anticipates that it will get closer to that being experienced in the commercial band.

    2010 NAB Show Call for Speakers
    Call for Technical Papers – NAB Broadcast Engineering Conference

    The 2010 NAB Show will host the 64th Broadcast Engineering Conference. This world-class conference addresses the most recent developments in broadcast technology and focuses on the opportunities and challenges that face broadcast engineering professionals. Each year hundreds of broadcast professionals from around the world attend the conference. They include practicing broadcast engineers and technicians, engineering consultants, contract engineers, broadcast equipment manufacturers, distributors, R&D engineers plus anyone specifically interested in the latest broadcast technologies.

    Do you have something to share?
    If you feel qualified to speak at the NAB Broadcast Engineering Conference, we invite you to submit a technical paper proposal. Not all acceptable submissions can be included in the conference, due to the large number of submissions that are received and the limited number of available time slots.

    The deadline for submitting your proposal is October 23, 2009. If you have any questions, contact John Marino, VP Science and Technology at 202 429 5346.

    PLAN TO ATTEND!
    The IEEE Broadcast Technology Society
    59th ANNUAL BROADCAST SYMPOSIUM
    14 -16 October 2009
    The Westin Alexandria
    Alexandria, VA, USA
    www.ieee.org/bts/symposium

     

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