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6-26. Switchable Lowpass Filters Test
This test checks the circuits in the signal path shown in Figure 6-18. In particular, the Switch-
able Lowpass Filter in each channel is tested. A signal is input to the 0-40MHz Input from an
-hp- 3325A opt 001; the output of Channel B is measured with a scope and an -hp- 3455A
Voltmeter. The -hp- 3325A opt 001 is then connected to the Noise Input of the -hp- 35601 A;
the output of Channel A is measured with the scope and voltmeter. All three modes of the
filters are tested: 100kHz, 1kHz, and 10Hz. The user is asked to confirm the shape of each
filter and the program checks for proper levels with the voltmeter. The results are printed.
Initializing the Test
With the Low Frequency Menu displayed, press SFK K5 to initialize the test. After initializa
tion, follow the instructions displayed on the computer.
What if the Test Fails?
Assuming the previous tests have passed, the most likely cause of failure is one of the
Switchable Lowpass Filters. "SWITCH" can be used to check the operation of the control
lines for the filters. Refer to Service Group One for schematics, component locators, and
circuit descriptions.
Example Wave Shapes
Channel A 100 kHz Low Pass Filter Shape
Channel A 1 kHz Low Pass Filter Shape
Sweep lOmS/div
ChA .2mV/div
ChB 5V/div
-hp-3325A: .1 S, 0 to 200 kHz Sweep Marker Amplitude
approximately -5dB
Sweep lOmS/div
ChA .2mV/div
ChB 5V/div
-hp-3325A: .1 S, 0 to 2 kHz Sweep Marker Amplitude
approximately -2dB
Channel A 10 kHz Low Pass Filter Shape
Channel B 100 kHz Low Pass Filter Shape
Sweep .lS/div
ChA .2mV/div
ChB 5V/div
-hp-3325A: 1 S, 0 to 20 Hz Sweep Marker Amplitude
approximately -3dB
Sweep lOmS/div
ChA .2mV/div
Ch B 5V/div
-hp-3325A: .1 S, 0 to 200 kHz Sweep Marker Amplitude
approximately -25dB
6-40
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