General Description
R&S
®
CMW-KM645
10
User Manual 1173.9740.02 ─ 04
A 50
μ
s time constant is used for FM broadcasting in Europe, North American FM
stations use a 75
μ
s time constant.
●
An A-weighting filter defined in IEC 60651. The A-weighting filter deemphasizes
the very low and very high frequency components of the sound in a manner similar
to the frequency response of the human ear and correlates well with subjective
reactions to noise. Thus, noise levels stated in terms of dBA reflect the response of
the human ear by filtering out some of the noise in the low- and high-frequency
ranges that the ear does not detect well. The A-weighted scale commonly is used
in local ordinances and standards.
●
A lowpass filter and a highpass filter with selectable cutoff frequencies. You can
use the highpass filter to eliminate a possible DC component in the audio signal
that may cause measurement inaccuracies.
●
A variable bandpass filter with configurable center frequency and bandwidth.
Each of the left and right channels from the FM stereo decoder (see
) is mea-
sured as shown below.
Fig. 3-2: Filters in the audio receive path
3.4 Limit Settings and Conformance Requirements
Conformance requirements for tests on FM signals are specified in the various stand-
ards; the following sections give an overview.
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Limit Settings and Conformance Requirements
深圳德标仪器
135-1095-0799
