IEEE 743-1984 pdf free.IEEE Standard Methods and Equipment for Measuring the Transmission Characteristics of Analog Voice Frequency Circuits.
IEEE 7433. measurement of signal power at an accesspoint of nominal impedance in a circuit. ‘Theimpedance may range from 135 to 1650 with 600 2 and 900 most commonly used.The expected signal levels at the access pointsusually range from -40 dBm to +10 dBm.
The frequency range of interest for normalspeech and voiceband data services may ex-tend from below 60 Hz to above 4 kHz. Forprogram circuits, the frequency range of inter-est may extend from 20 Hz to 20 kHz. Wide-band data circuits further extend this range(see 4.3.1 for measurement standards).
Noise and Signal-to-Noise Ratio. Measurements are made with the channel terminatedin its nominal impedance. A holding tone of1004 Hz (see 4.3.1.4) is usually transmitted,then notched out before the noise is mea-sured.The holding tone activates the channelso that harmonic distortion，quantizing noise,phase jitter，and amplitude jitter become partof the noise measurement. if no holding toneis transmitted,the result is a backgroundnoise measurement. If a holding tone is transmitted,the result is a noise-with-tone measure-ment or notched noise measurement. Noise-with-tone measurements give a measure of thenoise encountered by a continuous data signalor the noise a listener would hear during aspeech burst.Signal-to-noise ratio is a compari-son of the received power of the holding toneto the noise-with-tone (see 4.3.2 for measure-ment standards).Noise measurements are madeusing one of several frequency weighting net-works/filters.These include:
(1)C-Message. A filter frequency weightingwhich weights the noise according to its per-ceived annoyance to a typical listener，ofstandard telephone service.
(2)C-Notch. C-Message weighting with theaddition of a narrow stop-band or notchfilter centered at 1010 Hz.This measurementis used to make a dynamic evaluation of theeffects of noise on voice-grade services.
(3) 3 kHz Flat. When used on voice frequencycircuits，this filter permits the investigation ofthe presence of low-frequency noise (powerinduction, etc). It is a 3 kHz low-pass filter ofButterworth shape rolling off at 12 dB peroctave.
(4) Program. This filter is used for weightedmeasurements of noise on program circuitswith bandwidths up to approximately 8 kHz.(5) 15 kHz Flat. This filter is used when mak-ing unweighted measurements of noise on pro-gram circuits. It is a 15 kHz low-pass filter ofButterworth shape rolling off at 12 dB per oc-tave. It is not ordinarily used on voice messagecircuits.IEEE 743 pdf download.