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03.25.2003
Originally featured on BroadcastEngineering.com
Can NTSC data insertion hurt BTSC services?



PRO channel allows television stations to provide IFB to ENG truck via a subcarrier on the transmitted NTSC signal.

Modulation Sciences, has taken issue with Dotcast's November 2001 application for approval data insertion pursuant to Section 73.682 and December filings of additional field test reports with the FCC.

MSI objects to the use of the aural baseband as a component of its data injection system and requested that the commission suspend authorization to utilize the Dotcast system until it is proven that the system does not cause interference to operations of BTSC stereo, BTSC SAP and/or BTSC PRO channel components of the NTSC television signal.

MSI supplies the television broadcast industry with equipment used to create the Broadcast Television Systems Committee (“BTSC”) aural signal. That equipment includes television stereo generators and precision decoders, second audio program (“SAP”) generators and professional receivers, and Professional (“PRO”) channel generators and professional receivers. Additionally, they manufacture a precision visual and aural television demodulator.

Dotcast offers data distribution partnerships that can enable broadcasters to carve out additional possible revenue streams. By joining the Dotcast network, broadcasters commit part of their analog and digital spectrum move data from source providers to end users. In each local broadcast facility, Dotcast installs distribution servers with proprietary technology that make possible insertion of data into the unused analog or digital over-the-air broadcast signal. In return, broadcasters share in the revenue Dotcast earns from companies using the Dotcast Digital Network.

All television stations in the U.S. that broadcast in the MTS mode utilize the BTSC system. The FCC’s rules severely limit aural subcarrier transmissions at 15,734 Hz except for stations utilizing the BTSC system. The aural signal of the transmitted television signal tends to be very noisy, especially above 15 kHz. To mitigate the problem and increase the S/N companding, in which 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 the process is reversed. MSI reminded the commision that the goal of this process is to prevent excessive noise and to eliminate the effects of interfering signals, such as those created by the aural portion of the Dotcast dNTSC system by treating the dNTSC-generated interfering signals as simply additional noise.

But MSI in its statement to the FCC said that it is concerned that if the companding process is exposed to enough “noise” that a “cliff” threshold effect might occur in which those systems will suddenly cease providing any noise reduction at all and most consumer television receivers will automatically switch to monaural reception. This effect results in greater limitations on the coverage distance of BTSC stereo transmissions. The same reduction in service area occurs with respect to SAP transmissions. MSI also pointed out that the Commission’s Office of Engineering and Technology issued OET Bulletin No. 60, “Multichannel Television Sound Transmission and Audio Processing Requirements For The BTSC System," Revision A, February, 1986 (“OET-60”). OET-60 states that all measurements of stereo and SAP signals be made with all companding removed. MSI said that the Dotcast tests did not follow that requirement.

MSI is also concerned about similar effects on the BTSC PRO channel, which is used by many stations' ENG activities as IFB for the shot in the field. MSI said that it is essential that the commission and its television licensees know the extent to which Dotcast’s dNTSC system will adversely affect PRO channel operations.

For more information visit www.modsci.com and www.dotcast.com.

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