A precise, automated test system for video tape noise evaluation

An automated test system for tape noise evaluation in colour-under type video systems is described. The system, which is currently used for VHS media testing, allows thorough high-precision electromagnetic performance evaluation by non-technical personnel. An analysis of luminance and chrominance output and noise characteristics for a sample is completed in less than four minutes. A high-precision capability is included to perform digital trace averaging over a number of spectral measurements. The high-precision mode of operation allows measurement of luminance and chrominance output with a standard deviation of 0.2 dB and luminance and chrominance noise with a standard deviation of 0.5 dB. Digital storage of spectrum traces enables compensation for system noise to be made over a broad spectral range instead of a single frequency, and a numerical integration of the noise power in the signal channel is easily accomplished. Results presented show how the high precision of the measurement technique may be used to determine the rate of head accommodation to a particular tape.