Boonton 1121A, Instruction Manual

Page: 70 / 181

Section 5 Maintenance
5-8
5-35. Low-Pass Filter Accuracy.
The filter accuracy test
is made by setting an amplitude ratio reference at a
frequency of 1 kHz and adjusting the frequency at the
same reference level for a display of -3.01 dB or 70.7%.
The frequency is then measured and checked against the
specified limits.
5-36. Depress the LCL/INIT key to initialize the instru-
ment. Connect the output of the Test Oscillator to the
input of the Audio Analyzer and terminate the Analyzer
input with 600 ohms. Set the Test Oscillator to a fre-
quency of 1 kHz +/- 10 Hz and a level of 2 volts +/- 50 mV.
Enable the Analyzer level ratio mode and depress the dB
key. Perform the following procedure for each
low-pass filter listed in Table 5-12.
a. Enable the specified low-pass filter.
b. Adjust the Test Oscillator frequency toward
the corner frequency of the selected filter for a display
indication of -3.01 dB +/- 0.05 dB.
c. Check the frequency against the specified limits
and record the result, pass or fail, in Table 5-12.
5-37. Residual Distortion and Noise. In this test the
Source is connected to the Analyzer and the combination
of distortion and noise is measured at various frequencies
and levels. In this manner the Source and Analyzer are
measured simultaneously. If either the Source or
Analyzer is out of specification, a known to be good
source or analyzer may be substituted to determine which
part of the instrument is at fault.
5-38.
Depress the LCL/INIT key to initialize the instru-
ment and enter special function 75 (50 ohm output).
Connect the Source HI and LOW outputs using the
balanced cable and adapters to the Analyzer HI and LOW
inputs and connect the 50 ohm load across the binding
post adapters at the Analyzer input. Enable the input
floating mode and depress the DIST and DB keys. Set the
Source to the levels and frequencies listed in Table 5-13,
enable low-pass filter specified in the BW column and
record the results, pass or fail.
5-39. Residual Signal-to-Noise Ratio.
In this test the
Source is connected to the Analyzer and the residual
signal-to-noise is measured at various frequencies and
levels. Due to the synchronous nature of the measure-
ment only the Source and Analyzer of the same instru-
ment may be used together.
5-40. Depress the LCL/INIT key to initialize the instru-
ment and enter special function 75 (50 ohm output).
Connect the source HI and LOW outputs using the bal-
anced cable and adapters to the Analyzer HI and LOW
inputs and connect the 50 ohm load across the binding
post adapters at the Analyzer input. Enable the input
floating mode and depress the S/N key. Set the Source to
the levels and frequencies listed in Tble 5-14, enable the
low-pass filter specified in the BW column and record the
results, pass or fail.
5-41. Common Mode Rejection Ratio. Depress the
LCL/INIT key to initialize the instrument and enter special
function 75 (50 ohm output). Enable the input floating
mode and depress the Analyzer LEVEL key and dB key.
Perform the following procedure.
a. Connect the Source HI output to the Analyzer HI
input using the BNC cable.
b. Set the Source level to 2.500 volts at a frequency
of 1 kHz.
c. Enable the Analyzer ratio mode to set the common
mode signal reference.
d. Enter special function 12 to hold the 1.5 volt input
range.
e. Connect the Source HI output to both Analyzer HI
and LOW inputs using BNC cables and a Tee adapter.
f. Set the Source to the test frequencies and levels
listed in Table 5-15 and record the results, pass or fail.
5-42. Optional Filter Accuracy.
The filter accuracy tests
are made by setting an amplitude ratio reference at a
reference frequency and measuring the relative
amplitude at other specified test frequencies. The results
are then compared to the specification limits.
5-43. Optional Filter Test Connections.
The test
connection setup is identical for all the optional filter
performance tests. Depress the LCL/INIT key to
initialize the instrument and enable the Analyzer input
floating mode. Connect the Source HI and LOW outputs
to the Analyzer HI and LOW inputs using the balanced
cable and adapters. Enter special function 75 (50 ohm
source impedance) and terminate the Analyzer input with
50 ohms.