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AM5(e) Classic Instruction Manual
6.3.1 Units of Noise Measurement: For noise measurements, the voltage of the
received signal is measured with an RMS detector on an AM5 Classic. For an
AM5e Classic both RMS detection and Quasi-Peak (Q PEAK) detection is
available. Q PEAK detection (and appropriate filtering) is selected with the
FILTER key.
The voltage is first converted to dBm. The RX impedance selected determines the
voltage to dBm conversion.
In an AM5e Classic the dBm measurements are displayed in the left display. For
example, if the noise level were -40 dBm, the display would appear as follows:
SEND
MEAS
DISPLAY
In an AM5 Classic, the reading is further converted to dBrn (decibels relative
noise). The dBrn measurement is designed to present a 0 reading for an
optimally quiet line (-90 dBm) and is determined by the formula dBrn = dBm +
90. A –40 dBm noise level would read 50 dBrn on an AM5 Classic as below:
SEND
MEAS
DISPLAY
A comparison of dBm and dBrn units of measurement is shown in Figure 3-3
and below:
Relative zero reference for dB readings can be
established at any point. Example below.
0
-90
-80
-70
0
+10
+20
-90 dBm for zero reference point of d B r n noise measurements.
November 19, 1997
(18-0047)
-60
-50
-40
-30
+30
+40
+50
+60
Page 6-3
MEASURE FUNCTIONS
dB
dBm
mSEC
HOLD TONE
dB
dBm
dBrn
mSEC
HOLD TONE
Intensity of 1 milliwatt of power
+50 dB
-20
-10
0
+70
+80
+90 +100 dBrn
KHz
SEC
MIN
CNT
KHz
SEC
MIN
CNT
+10
dBm
2/26/93
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