ITU-R S.481-2 FRENCH-1986 Measurement of noise in actual traffic for systems in the fixed-satellite service for telephony using frequency-division multiplex
The CCIR considering: (a) that measurements by means of a generator producing white noise (Recommendation 482) are only possible when the radio-frequency channel is not carrying traffic; (6) that systems carrying multi-channel telephony cannot be withdrawn from service for measurement at will; (c) that protection channels, similar to those used in terrestrial radio-relay systems, are not available for maintenance purposes; (d) that maintenance measurements of the total noise (thermal and intermodulation noise) are useful for determining the quality of a system and must be made while the system is carrying traffic; (e) that it is convenient to place the channels used for this kind of measurement outside the total bandwidth of the multiplex signal; (f) that, when these measuring channels are located outside the total multiplex signal band, they should be positioned as near the limits of the total signal band as possible, to measure the intermodulation products due to the non-linearity of the system; (g) that, on the other hand, to facilitate and to minimize the cost of filter construction, the measuring channels should not be positioned too near these limits; (h) that measurements in channels about 10% above the upper limit of the totai multiplex signal band are generally sensitive to changes of thermal and intermodulation noise in the radio-frequency and intermediate-frequency circuits of the equipment; (j) that it is usually necessary to use band-stop filters at the input of the system to minimize noise on the incoming circuit in the bands occupied by the measuring channels, and that it will be necessary to specify the minimum performance of these filters, both in the stopband of these filters and at the edges of the total multiplex signal band.
ITU-R S.481-2 FRENCH-1986 history
1986ITU-R S.481-2 FRENCH-1986 Measurement of noise in actual traffic for systems in the fixed-satellite service for telephony using frequency-division multiplex