A method of measuring noise levels on short-wave radiotelegraph circuits

This method is essentially a means for continuously measuring the percentage of elapsed time during which the noise level exceeds a certain predetermined voltage level. The predetermined voltage level may be made any level at which data are desired. The device consists of a biased tube circuit such that when input signal exceeds a certain level, the output tube passes a normal value of plate current through a ballistic meter of slow period. If the input continuously exceeds the threshold level, the ballistic meter reads “100 per cent.” The data obtained are particularly useful in connection with the engineering of short-wave radiotelegraph circuits, since these are usually operated through vacuum tube relay devices at the receiving end, set to register normal output whenever¹ the signal “marks” at any level above a controllable threshold value.