Aeroflex 2944B - Distortion Measurement

LOCAL OPERATION
3-65
Distortion measurement
The distortion measuring facilities of the monitor are available within the AF TEST mode.
Pressing the [Audio Meter] key, to change the soft keys as shown in fold out diagram (6
-3), then
pressing the [Dist/S-N]soft key, accesses the distortion measurement menu shown in fold out
diagram (6-3-2).
Pressing each of the soft keys will have the following effect:
Off
Disables any active distortion measuring function.
Hint. By disabling this function, the time taken to measure the remainder of the measurement functions is
shortened thereby reducing the update time.
S/N
Selects signal to noise ratio as the measurement method. The AF generator is disabled and
enabled alternately by the monitor software and the total output level from the circuit under test is
measured by the AF voltmeter at each state. See Fig. 3-7 a, & d Distortion level and signal to
noise level measurements, on page 3-36.
Calculations are performed by the software to calculate the signal to noise ratio using the formula:
S/N
= 20
1
2
log
V
V
dB
=
++
20 log
()S
N
D
N
dB
The distortion bar chart ranges available are 0 to 30 dB and 0 to 100 dB. The signal to noise ratio
is displayed as a digital read-out above the bar chart. The AF test menu is recalled automatically
after pressing this key.
SINAD
Selects SINAD as the measurement method. The AF generator is set to 1 kHz and the 1 kHz
distortion notch filter is switched alternatively in and out of circuit, with the signal level being
measured by the AF voltmeter in each state. See Fig. 3-7 a, b, & c, Distortion level and signal to
noise level measurements, on page 3-36.
The monitor software calculates the SINAD level according to the formula:
SINAD
= 20
1
2
log
V
V
dB
=
++
+
20 log
()
()
S
N
D
ND
dB
The distortion bar chart ranges available are 0 to 18 dB and 0 to 50 dB. The SINAD level is
displayed as a digital readout above the bar chart. The AF test menu is recalled automatically after
pressing this key.