Operating instructions

LOCAL OPERATION
3-67
Dist’n
Selects distortion percentage 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. 3-10 a, b, & c, Distortion level and
signal to noise level measurements, on page 3-36.
The monitor software calculates the distortion level according to the formula:-
Distortion
= 100
2
1
V
V
%
=
+
++
100
()
()
%
N
D
SND
The distortion bar chart ranges available are 0 to 10% and 0 to 30%. The distortion percentage
level is displayed as a digital readout above the bar chart. The AF test menu is recalled
automatically after pressing this key.
*Oscilloscope*
The oscilloscope facility can be used from within the AF test mode to examine the signal present
at the AF input socket. The sensitivity of the Y axis is adjustable from 10 mV/division to
20 V/division in a 1,2,5 sequence.
The input to the oscilloscope is taken directly from the AF input, and not through any of the AF
filters. Therefore measurements obtained on the AF voltmeter will show the effects of filtering,
whereas those made using the oscilloscope will not.
A section on the use of the oscilloscope facility starts on page 3-89.