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Clear Channel Radio Reduces AM Audio Bandwidth; Littlejohn to Propose Change to NRSC for All AMs

Clear Channel Radio Reduces AM Audio Bandwidth; Littlejohn to Propose Change to NRSC for All AMs

Jeff Littlejohn wants his company to do its part to clean up the AM analog band.
In order to accomplish that, Radio World Online has learned, Clear Channel Radio’s senior VP of engineering has made it a policy for the company’s AM stations to reduce their bandwidth to match the bandwidth of available receivers to 5 kHz for AM talk stations and 6 kHz for AM music stations.
Littlejohn also is co-chairman of the AM Subcommittee of the NRSC. In that role, at a meeting of the standards group at next week’s NAB Radio Show, he plans to propose that all AM licensees follow suit.
After two years of studies, Littlejohn says he has concluded that it serves no purpose for AMs to continue broadcasting 10 kHz audio on the AM band when the average receiver has an audio response of less than 4.5 kHz.
In a memo to Clear Channel regional engineers outlining the new operating procedure, Littlejohn cites the benefits of the change: increased modulation efficiency and reduced interference to first-adjacent frequencies.
Also, “AM modulation that falls outside of a receiver’s usable bandwidth ends up increasing the noise floor within the audible bandwidth,” states Littlejohn in the memo.
Though consumers won’t be able to tell the difference on the average car radio, Littlejohn told RW Online, increasing the modulation efficiency will improve the audio.
“Getting rid of the high frequencies allows you to turn up the modulation, (which) will make it louder but not more distorted,” said Littlejohn.
As far as reducing the bandwidth reducing interference to neighboring stations, he gave an example. WHP 580 kHz in Harrisburg interferes with WTNT 570 in Washington.
Listeners to WTNT can “start hearing chatter from WHP because WHP is transmitting in 10 kHz bandwidth. If it were lower, you wouldn’t hear that, you would hear WTNT better,” he said.
For all AM stations operating with modern audio processors, the Orban 9200, Omnia 4.5, Omnia 3, Omnia 3 CC, Clear Channel will reduce its audio bandwidth: 5.0 kHz audio bandwidth for all non-music intensive AMs; 6.0 kHz audio bandwidth for AMs with a music intensive format.
Why the difference? Music station listeners may have more wideband radios, such as the GE SuperRadio (in Wide Band mode) so going with a 6 kHz audio bandwidth “kind of negates degradation to those stations,” said Littlejohn.
Those who might object to such a change would be listeners who own antique radios, he said. He notes that although he owns some, he acknowledges he doesn’t spend the majority of his radio listening time using the antiques.
Feedback he’s received on the change from chief engineers of other radio group owners has been positive, he said.
“Several echoed that they had done this for awhile. They realized they could be louder without degradation,” he said.
Littlejohn said the change would occur at Clear Channel quickly. Half a dozen stations had switch to the new audio bandwidth as of Wednesday and more were expected to make the change Thursday. Some of his engineers acknowledged they had made the change on their own initiative in advance of the directive, he said.
“They were thinking ahead of everybody else,” he said in praise.
As far as the proposal to the NRSC, Littlejohn said the group would likely want to do its own studies in order to support what the body decides about changing the industry standard.