Seventeen members of The Detroit Section met at WKBD-TV on December 12th for a presentation dealing with Bandwidth Enhancement in 8VSB Transmission by David Neff of ADC Broadcast Systems Division.
A brief overview of some of the types of Non-DTV Broadcast signals adjacent to DTV channels 2, 4-6, 7, 13, 14, 36-38 and 51 such as Land Mobile, Non-Commercial FM and Radio Telescope Operations were identified as potential sources of interference.
The concept of Bandwidth Enhancement Technology involves the creation of a type of guard band by reducing the 8VSB signal by up to 200kHz at the edges. By allowing sharper filters to be used, edge attenuation can be reduced by 30 to 60 dB protecting adjacent services.
In the NTSC world, out of band products can be greatly reduced by the use of band pass and notch filtering. Not so with 8VSB. There is necessary information that lies outside of the pilot and Nyquist points of the spectrum that, if lopped off, would confuse an 8VSB demodulator. One solution is to move this Spectral Tail Energy to an area just inside the band. By replacing the removed energy from outside with equivalent energy at mirrored frequencies inside, the resultant signal can be demodulated as though it were identical to the original 8VSB signal.
The design process for arriving at compatible narrow band 8VSB was then described and resultant effects were shown at both the lower and upper channel edges. A more conventional technique of Brute Force Spectral Truncation was also described and compared to BET. We were shown that with the more conventional technique, reliance on transmitter and receiver equalization using large and expensive filters were required to correct the I channel. With BET, the correction is already built in, requiring only conventional filtering, rendering the narrow band I channel identical to standard 8VSB. Receivers from Panasonic, Sony, Philips, Thomson and Zenith have been tested.
The Detroit Section wishes to thank David Neff of ADC and our host, WKBD-TV for their seasonal hospitality and extends wishes for a Happy New Year to all our friends at SMPTE.