Proponents Push for FM HD Asymmetric Power

NAB FASTROAD says iBiquity Lab tests on asymmetric operation characterize improvement in digital SNR.
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NAB FASTROAD says iBiquity Lab tests on asymmetric operation characterize improvement in digital SNR.

Public comments filed at the FCC overwhelmingly support the notion of routinely allowing FM stations transmitting an HD Radio signal to raise their power levels unevenly. Right now, those stations need a waiver from FCC rules to operate with asymmetric, rather than symmetric, digital sideband power levels.

The digital power increase authorized last year allowed all FMs to raise their digital power by 6 dB (from –20 dBc to –14 dBc), with some broadcasters able to increase digital power by 10 dB (to –10 dBc) depending upon distance separations from first-adjacent stations. Proponents believe more FMs could do so if allowed to raise their digital power unevenly to protect neighboring stations from possible interference.

Comments to Docket 99-325 were due Monday. Seven filings representing a total of 10 broadcast groups, as well as the NAB, were filed.

A joint filing represented Beasley, CBS Radio, Emmis, Entercom, Greater Media, Journal, Lincoln Financial and Radio One as well as manufacturers Continental, Harris and Nautel. In it they wrote “implementation of this creative and flexible approach will allow more FM broadcasters to increase HD Radio power to the maximum permissible levels,” helping the continued rollout of HD.

In a separate comment, Crawford Broadcasting DOE Cris Alexander cited two examples where interference ended when digital power levels were changed from symmetric to asymmetric operation, amounting “to a more efficient use of spectrum” he told the FCC. Alexander is also a RW contributor.

Not all the comments favored the proposal. Jonathan Hardis, a member of the NRSC who works for NIST but wrote as an individual, opposes allowing stations to raise their digital power levels asymmetrically. The record does not support the request, and the commission should instead develop a “complete technical standard” for IBOC, he states.

NAB included a report describing lab testing of the concept conducted by iBiquity Digital and funded by both the technology developer and NAB FASTROAD. NAB said in its comments the test results in “HD Radio Asymmetric Sideband Laboratory Test Report," characterizes improvement in digital signal-to-noise ratio that can be realized with the use of asymmetric IBOC transmission power.

— Leslie Stimson