Abstract
IN investigations of the visibility of random noise in television pictures1,2, it has been found that for narrow-band noise which is just visible the required noise power increases by about 20 db. as the centre frequency is raised from 0.15 to 2 Mc./s. For frequencies between 2 and 3 Mc./s., the noise power remains nearly constant1, or shows a small fall2. It has been suggested1 that this may be because of the generation of intermodulation products of low-frequency noise, due to the non-linearity of the voltage/brightness characteristic of the television tube. These low-frequency products should be much easier to see than the original high-frequency noise. It follows that the non-linearity should also affect visibility of noise if a sinusoidal signal, together with noise, is applied to the tube control-grid. In this case, sum and difference frequencies of the signal and noise should be produced. An experiment which appears to demonstrate the expected intermodulation effect has been carried out.
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References
Post Office Radio Report No. 2289 (1955).
Maurice, R. D. A., Gilbert, M., Newell, G. F., and Spencer, J. G., B.B.C. Engineering Division Monograph No. 3 (1955).
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FATEHCHAND, R. Visibility of Noise on Television Pictures. Nature 181, 1797 (1958). https://doi.org/10.1038/1811797a0
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DOI: https://doi.org/10.1038/1811797a0
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