20.7.4.6 Weighted noise power in pWOp

The total weighted intermodulation noise power can be determined from Equation 20.23, where x = all products, (A+B), (A-B), etc.

20.7.4.7 Determination of unlinearity noise using spectral densities

The problem with Bennett's method is the difficulty of dealing with shaped frequency spectra (pre-emphasis at the output of Line re­peaters for instance.)

A method using spectral densities (Bell, 1971) overcomes this difficulty and can be extended to include the shape of the H^ and H across the band.

From Equation 20.10 the ratio of the total second order distortion voltage to the fundamental signal at the output of the amplifier or system is given by Equation 20.24, where v is the system input signal (assumed Gaussian).

The terms in Equation 20.24 can be expressed as a power in volts squared where S (f) and S (f) are the power spectral densities in volts squared per Hertz. S (f) is the figure for the multichannel input signal voltage, v., and S₂(f) for the input signal voltage squared, v?. This is shown in Equation 20.25.

If v is assumed Gaussian then Equation 20.26 may be obtained, ignoring d.c. terms and where represents the convolution integral.

The second order noise power NP₂ in watts is therefore given by Equation 20.27, where Pch is the traffic load per channel in watts.

Likewise the third order noise power NP in watts is given by Equation 20.28, where the mean square voltage is given by Equation 20.29 and Pch is the traffic load per channel in watts.

The convolution is best performed numerically on a per system basis.

1 Learn the words & word combinations:

Prophometric weighting	Псофометрическое взвешивание
Weighting factor	Весовой коэффициент
Gaussian noise	Нормальный шум
Boltzmann constant	Постоянная Больцмана
Circuit element	Элемент цепи
Transmission band	Полоса пропускания
Activity factor	Коэффициент активности
Traffic volume	Интенсивность движения
Trunk network	Сеть магистральных линий связи
Transfer characteristic	Переходная характеристика
Multichannel load (multiplexed)	Информационная нагрузка многоканальной системы
Correction factor	Поправочный коэффициент Коэффициент исправления
Convolution integral	Интеграл свертки
Traffic load	Информационная нагрузка (трафик)
Wire point	Место присоединения, монтажная точка

2 Read & translation the text (orally) 20.7:

3 Find Russian equivalents:

noise contributions	the topical entity
the virtual outgoing switch point	the degree of annoyance a channel of interest
random movement of electrons	a traffic load channel
single channel load figure	loud & soft talker factor
shaped frequency spectra	full channel width

4 Find English equivalents:

шум	тепловой
определить (оценить) с точки зрения передачи	подходить допускается
цифра силы шума	первоначальный
точное значение	средний
сопутствует возникновению	снижение
реорганизованный	действительны
весовой коэффициент