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 solidstate FM+IBOC transmitter to amplify both signals.
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 with some manufactures you should be able to implement IBOC by adding an exciter and
making very few or no modifications. Other solidstate transmitters may require modifications
ranging from minor to major. And tubetype 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 highlevel combining. To implement IBOC, you'll
purchase an IBOC transmitter and a highlevel combiner when you are ready.
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 latemodel, solidstate FM
transmitters, once the transmitter is converted it no longer will be able to make its original rated
power. (An IBOConly 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.
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
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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.
6. What does it take to ensure signal linearity?
To ensure linearity, IBOC transmitters employ some level of precorrection or filtering to overcome
distortion products created by nonlinearities in the system. Wellimplemented precorrection 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 precorrection may actually eliminate
the need for external bandpass filters or, if a filter is needed, result in a simpler and lower
cost filter.
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 solidstate 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 (highlevel 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 costeffective 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.
8. Will I need a new antenna?
Again, you will need to evaluate your specific situation. General guidelines follow.

AM: Nondirectional 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, symmetryenhancing 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
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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.
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 offtheboard 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?
10. I'm feeling overwhelmed by all I need to learn about IBOC. Who can help?
Broadcast Depot 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.