SE356602

1,264,134. Testing telecommunication systems. MARCONI INSTRUMENTS Ltd. June 26, 1969 [Aug.14, 1968], No.38861/68. Heading G1U. A multi-channel telecommunication system is tested for cross-talk by applying to the system an input signal in the form of a white noise spectrum from which a variable narrow frequency band has been eliminated and detecting whether any signal in this band is received at the system output. The input signal generator comprises a source 1 providing white noise over a certain frequency range, from which a fixed narrow band is eliminated by filter 2. The resulting signal is mixed at 3 with a higher-frequency signal from oscillator 4, and part of the output of a mixer 3- e.g. half of the lower sideband - is selected by a band-pass filter 5 and mixed with a further signal of fixed frequency from oscillator 7 to provide the required system input signal. The frequency of the eliminated band in this signal may then be varied by varying the frequency of oscillator 4.