McDewey

interest. "White noise" is a signal that contains all the audio frequencies in equal amounts, but which manifests no recognizable pitches or tones This figure illustrates, in a very general and simplified way, how a test−tone transmission is set up and how test tones are generated and measured (demarc A to demarc B). The equipment is set up to test the circuit between the demarc at A and the demarc at B. You are going to measure 1004 Hz loss inherent in the circuit between A and B. The bridging clips at both demarcs are removed in order to isolate the segment of the circuit under test. At A, an oscillator is attached to transmit and receive leads (also called tip and ring leads). At B, a transmission measuring set (TIMS) is attached to transmit and receive leads. The oscillator at A is set to generate a pure test tone with a power of 1 mW at 1004 Hz. At demarc B, the TIMS is set to read power in the range of 1 mW. The power reading at B is 0.5 mW. Therefore, the power lost between A and B is: 1 mW  0.5 mW = 0.5 mW A more useful way to express the loss is in terms of the relative loss, or the ratio between power out (B) and power in (A): Relative loss = Power out (B)  Power in (A)