Measurements of the Subjective Effects of Interference in Television Reception

A measurement program was conducted in which almost 200 observers made about 38,000 rating observations on color and monochrome stationary television pictures impaired by various known amounts of interference. Separate tests were made for the following types of interference: upper adjacent channel, lower adjacent channel, random noise, co-channel with each of six carrierfrequency separations, and simultaneous random noise and cochannel. Six rating grades were used as follows: 1) Excellent, 2) Fine, 3) Passable, 4) Marginal, 5) Inferior, and 6) Unusable. The observations were handled on a statistical cumulative frequency basis and plotted on probability paper. Commercial monochrome and color receivers were used, and the tests were made with laboratory signal-generating equipment on the lower VHF television channels. As representative results, a picture impaired by upper-adjacentchannel intereference (with 6-mc channels) was rated by 50 per cent of the observers as Passable or better for -27-db ratio of signal to interference. For the lower adjacent case a similar value was found, this result being explained as due to better traps in the medium-high-grade receivers of the test than in many receivers in use by the public. For random-noise interference the requirement for Passable or better rating by 50 per cent of the observers was +27 db on the basis of RMS sync amplitude to RMS noise over the 6-mc channel.