HP 4934A User Manual

Message Circuit Noise
Principles
The measurement uses no test signal and quantifies background noise with a
choice of band limiting filters (C-Message, 3 kHz Flat, 15 kHz Flat, Program
and 50 kBit).
C-Message: This filter weights noise in the same way it would be heard by a
telephone user. However, it is also used to evaluate the effects of noise on
voice-grade data circuits because its response is relatively flat over the fre¬
quency range for data transmission.
3 kHz Flat: This filter attenuates much less at low frequencies (60 Hz to 500
Hz) than the C-Message filter. By performing a 3 kHz measurement after a
C-Message measurement, the effect of low frequency noise (60 Hz commer¬
cial power, 20 Hz ringing, etc.) can be determined.
RESPONSE OF C-MESSAQE FILTER
RESPONSE OF 3KHz FLAT FILTER
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FREQUENCY lH?l
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FREQUENCY iHzt
15 kHz Flat: This filter is used when measuring noise on program channels
used in the broadcasting industry. Like the 3 kHz Flat filter, it passes low fre¬
quency noise.
Program: This filter is used when measuring noise on program channels
used in the broadcasting industry to communicate between the studio and
transmitter site.
50 kBit: This is a weighted filter used to measure noise on wideband data
circuits.
2-10 Making Measurements

HP 4934A Specifications

General

Brand	HP
Model	4934A
Category	Measuring Instruments
Language	English