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ATSC Digital Terrestrial TV Modulator

The ATSC Terrestrial TV standard is based on an 8-VSB modulation with pilot insertion. The sequence of 8 level symbols with levels ±1, ±3, ±5 and ±7 is the input to the 8-VSB modulator. The symbol rate is 10.762 Msb/s. The modulator has to modulate these symbols using VSB modulation and form the VSB spectrum that fits within a terrestrial 6 MHz channel.

8-VSB Signal Spectrum

Fig.1 8-VSB signal spectrum


To form this spectrum, the 8-VSB modulator has to process symbols by real and imaginary VSB filters and create a complex 8-VSB spectrum. The real VSB filter is a bypass filter that is just a delay block. The pilot insertion happens by adding a constant value to the input filter. For ATSC the standard pilot value is 1.25. The rolloff of the spectrum and respectively of the imaginary filter has to be 0.115.

8-VSB Modulator

Fig.2 8-VSB Modulator


After modulation to the intermediate frequency fIF the signal is then shifted to radio frequency (RF).

8-VSB Real and Imaginary filter frequency responses

Fig.3 8-VSB Real and Imaginary filter frequency responses

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VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713