Measurement of 8-VSB DTV transmitter emissions

This paper describes the theory and procedures necessary to understand and measure the emissions of an 8-VSB DTV transmitter. It starts with the FCC's requirements, then moves to the nature of the 8-VSB signal. The noise bandwidth of the signal is calculated and it is demonstrated how to relate this bandwidth to the FCC's requirement that the out of channel emissions be measured in a 500 kHz bandwidth. This discussion justifies the measurement procedure provided, showing how a spectrum analyzer or other specialty 8-VSB measurement equipment may be used to determine compliance with the FCCs out of channel emissions requirements. Methods of achieving measurements to the FCCs -110 dB specification are discussed. Effects of several factors that may affect measurement accuracy including measurement bandwidth, intermodulation, noise floor, logarithmic amplifier error, detector error and mismatch errors are discussed. An appendix gives an easy method for approximating the power of the 8-VSB signal by adding 12 dB to the pilot signal amplitude. The appendix also derives the relationship between the amplitude of the pilot signal and the bandwidth-dependent amplitude of the head of the 8-VSB signal.