Does your 2011 project list include either adding IBOC for the first time, or otherwise taking advantage of the new rules with respect to the allowable IBOC power? If so this article is for you. In reality the solutions to either of those two problems are nearly identical – as usual it depends upon your transmitter site particulars.

Of course the very first thing to do is to determine just how much IBOC power you can now run. As of May 10 2010, most stations were allowed to run up to -14dBC without giving prior notice to the Commission. (After higher-power operations commence, the station has 10 days to send the FCC an informal letter informing them of the change.)

Details on the power upgrade.

It is quite possible that your station may be able to run more than the “blanket” increase – in other words, some power level between -14dBc and -10dBc. Bear in mind that the results of those calculations may show that your station can run more power in one group of sidebands than the other. You will need to file a request with the Commission prior to increasing IBOC power to beyond the -14dBc blanket power level; see FCC Public Notice DA 10-866 for the fine details.

Details of variance in power level in FCC order 99-325.

Once you’ve determined the amount of IBOC ERP that will be allowed, you will need to file an informal request of the Commission before doing so. It is also possible that -20dBc is the IBOC limit for your super-power station.

What super-power stations need to know.

Interference

Before you plan out and build your higher-power IBOC transmission system it is important to know that there is at least the potential for interference between your new digital facility and an existing analog facility. The FCC Order 99-325 not only spells out the details of the IBOC power increase, but also the means by which interference from digital transmissions to analog transmissions will be mitigated. It is possible that you will need to throttle back to the original -20dBc level (but no lower) to mitigate the interference. That being said, paragraph 14 of the order reads as follows: "Since the commencement of 1 percent FM IBOC Power operations in 2004, the Bureau has not received any well documented complaints of interference to analog FM stations from digital signals. Since May 2006, the Media Bureau issued a total of 15 experimental authorizations to permit operations at up to 10 percent FM IBOC Power, including authorizations for 10 grandfathered short-spaced stations with as many as four first-adjacent channel short spacings. Some of these short spacings are severe. These stations operated their FM digital facilities with different levels of increased FM digital ERP throughout the experimental period, with the preponderance of the time spent operating with the maximum permissible FM digital ERP of -10dBc. The Bureau did not receive any complaints of interference to analog FM stations from licensees of analog FM stations or the listening public as a result of the experimental operations."

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