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03.02.2006
Originally featured on BroadcastEngineering.com
FCC rules for DTS should not allow additional interference, says MSTV

The Association for Maximum Service Television filed comments Feb. 9 with the FCC asking it to avoid establishing rules for Distributed Transmission Systems, DTS, that would allow broadcasters to arbitrarily expand their coverage area or cause additional interference to neighboring stations.

In the petition, MSTV endorsed DTS because of its ability to bring broadcast service to viewers in hilly and underserved areas where there are gaps in coverage; however, it cautioned the commission that these benefits “must be carefully weighed against the risk of DTS in causing harmful interference.”

The MSTV filing favored the commission’s proposal to license DTS on a primary basis. Otherwise, broadcasters and viewers who would benefit from DTS might not because broadcasters would have a regulatory disincentive to set up distributed transmission, which would have to accept interference as a service licensed on a secondary basis.

However, regardless of being licensed as a primary service, DTS service should not be allowed to cause additional harmful interference, the association said.

MSTV also urged the commission to license DTS operations on a linked group basis covered by one construction permit rather than licensing each DTS transmitter separately. The association also recommended that stations be allowed to add DTS transmitters using a minor change application.

The association favored a commission proposal to require one DTS transmitter to cover the station’s community of license, but urged the commission to give the Media Bureau the flexibility to grant waivers to such a rule if an alternative arrangement would provide equal or better coverage of the principal community.

Any rules to establish DTS service should not increase interference to viewer reception by raising the spectral noise floor, MSTV said. Therefore, commission rules should not allow aggregate interference from all of the transmitters in a DTS system to exceed applicable limits for a single transmitter in a conventional broadcast system.

Additionally, the method used to calculate interference from a single transmitter isn’t capable of measuring interference in a DTS system, according to MSTV. OET-69 was not designed for this purpose. It relies on certain assumptions about transmitter placement relative to their channel relationship within a geographic area. OET-69 “did not include a technique to compute interference based on the placement and operation of transmitters anywhere within the service area of adjacent channel DTV stations, or consider the aggregate effect of multiple DTS transmitters in the same area,” the MSTV filing said.

The association proposed a couple of modifications to OET-69 to make it suitable for determining interference from DTS systems. First, a “variable protection ratios (D/U)” component should be included in computing interference. Second, the MSTV proposed a way to account for multiple DTS transmitters in a given “market by aggregating their signal for interference computation.”

For more information, visit www.mstv.org.

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