GB1082566A - Method of, and circuitry for, the measurement of intermodulation noises - Google Patents

Abstract

1,082,566. Measuring intermodulation noise. TAVKOZLESI KUTATO INTEZET. April 22, 1965, No.17134/65. Heading G1U. In an arrangement for measuring intermodulation noise occurring in a system to be tested, such as a microwave system designed for the transmission of multichannel telephone signals, a noise voltage having a frequency spectrum which contains substantial drops in level at a number of frequencies is applied to the input of the circuit to be tested, and the noise voltages occurring at these frequencies at the output of the system are detected and displayed simultaneously. The noise generator, Fig. 5(a), contains a thermal noise source N and high and low pass filters L, H to define the bandwidth of the noise. The noise band may be supplied to the output of the generator either directly (with the switch Sw in the position 1) or via a series of band stop filters S1-Sw which remove the noise signal at their particular tuned frequencies. The noise spectrum from the generator is passed via the system under test to the input of the noise receiver (Fig. 5(b)) where after passing an attenuator A the signals are passed via a branch network DN to the parallel receivers Rl-Rn each having a frequency corresponding to that of one of the filters S1-Sw and all having the same gain. The output voltage of each receiver is displayed on the indicators I1-In. To use the arrangement, the full frequency spectrum is first transmitted, with switch Sw in the position 1, the attenuator A is set to give high attenuation and the reading on any indicator is noted. The filters S1-Sn are then inserted into the generator circuit, and the attenuator adjusted to give the same reading on a particular instrument. The noise ratio at the frequency represented by this indicator may then be read from the attenuator scale, while the readings on the other indicators will enable the corresponding noise ratios to be determined.