Voiceband data transmission measurements.

CFR · 2024-01-01 · US · Title 7

(a) The data transmission measurements listed in this section shall be used to determine the acceptability of trunk and nonloaded subscriber loop circuits for data modem transmission. (b) (2) S/CNN is the logarithmic ratio expressed in dB of a 1,004 Hz holding tone signal compared to the C-message weighted noise level. S/CNN is one of the most important transmission parameters affecting the performance of data transmission because proper modem operation requires low noise relative to received power level. Since modulated carriers are used in data communication systems, noise measurements need to be performed with power on the connection to activate equipment having signal-level-dependent noise sources. For 4 kHz channels, a 1,004 Hz holding tone is used to activate the signal-dependent equipment on the channel or connection. (3) (4) (5) (6) (7) (c) (2) S/IMD is a measure of the distortion produced by extraneous frequency cross products, known as intermodulation products, when a multi-tone tone signal is applied to a system. (3) Intermodulation distortion (IMD) is caused by system nonlinearities acting upon the harmonic frequencies produced from an input of multiple tones. The products resulting from IMD can be more damaging than noise in terms of producing data transmission errors. (4) IMD is measured as a signal to distortion ratio and is expressed as the logarithmic ratio in dB of the composite power of four resulting test frequencies to the total power of specific higher o

official document · source cfr-2024 · id 7:§ 1755.405