Dotcast technology may hurt PRO channel operations

Modulation Sciences is opposing a submission to the FCC that could cause interference to several broadcast operations.

MSI opposes a recent submission by Dotcast, a broadband media delivery and management services company. Dotcast submitted an “Application for Approval of System for Insertion of Non-Video Data Pursuant to Section 73.682,” last November. Dotcast's letter and reports were filed December 27, 2002.

MSI has filed a request with the FCC asking the Commission to suspend the use of systems designed to insert digital data into standard NTSC broadcasts. MSI said Dotcast's dNTSC system might cause signal interference to operations of BTSC stereo, BTSC SAP and/or BTSC Pro channel components of the NTSC television signal. MSI wants the FCC to suspend the use of the dNTSC system until further testing can be complete.

Modulation Sciences' Model MSI-3300 television audio processor AES/EBU/Analog (TOP) and SAP receiver. The company warns that a new system may cause signal interference to operations of BTSC stereo, BTSC SAP and/or BTSC Pro channel components of the NTSC television signal.

A review of Dotcast’s submissions, according to MSI, discloses no indication that any aural tests were performed with companding removed, as required by OET-60. As a result, it is impossible to determine whether Dotcast’s system complies with the technical standards set out in Section C of OET-60. Such compliance can be gauged only through OET-60-compliant testing, i.e., testing with companding removed.

MSI is concerned with Dotcast’s use of the aural baseband as a component of its data injection system. MSI said all television stations in the United States, which broadcasts in the MTS mode, use the BTSC system. The Commission’s rule's severely limit aural subcarrier transmissions at 15,734 Hz (+2 Hz) except for stations utilizing the BTSC system, according to MSI.

MSI also noted several technical reasons as to why the delay should be implemented:

  • Aural signal of television stations tends to be very noisy, especially above 15 kHz
  • The standard method of addressing this problem and reducing the impact of noise on a desired signal (i.e., improving the signal-to-noise ratio) is “compandoring” or “encoding”
  • Before transmission the “difference” channel carrying the aural stereo information is greatly compressed in its amplitude range and increased in level
  • At the receive point of the transmission a reverse process takes place, restoring the signal to its original form

Companding is effective at removing not only noise, the company said, but also interfering signals, such as those created by the aural portion of the Dotcast dNTSC system.

In regards to the PRO channel, MSI said Dotcast does not address the possible impact which operation of the dNTSC system might have on that channel.

The PRO channel, according to MSI, is vital to many stations as an essential element of their electronic newsgathering (“ENG”) activities. About 300 stations, mostly in major markets, use the PRO channel to permit communication between production personnel and on-air personnel reporting from remote locations.

According to MSI, there are no suitable substitutes for use of PRO channel, especially in the ENG context. Land mobile channels are too scarce and its signal reach is too limited, to accommodate the extensive sharing which would be necessary to cover a major news event. Other alternatives are similarly limited and subject to congestion and non-availability, especially in times of crisis when ENG coverage would be necessary.

MSI said the Commission and its television licensees will need to know the extent to which Dotcast’s dNTSC system will adversely affect PRO channel operations.

At this time, MSI said the Commission lacks sufficient information about the dNTSC system’s effect on stereo, SAP and PRO operations to permit the continued authorization of the dNTSC system. Until testing in conformity with the standards set out in OET-60 has been completed and its results fully considered, the Commission should suspend its previously granted authority to use the dNTSC system.

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