The output of the filter goes two ways: to potentiometer P2 for level control and output buffering and to P3, a resistive trimmer that controls the level at pin 3 of the input jumper-selector JP1. This branch allows the looping of a portion of the output signal to the input, for purposes that shall be studied in the subsequent Worksheets.
- At this moment, operation as a filter is required so place jumper JP between pins 1 and 2 and ignore P3.
- Turn P2 fully clockwise maximum output level). Connect a dual-channel oscilloscope with Y1 to display the input signal and Y2 the output. Apply the signal from a low-frequency sine wave generator to the input. Select a signal that has amplitude of 100mvpp and a frequency of 500Hz approx.
- Adjust P1 (frequency control) mid-way. Do not re-adjust P1 during the subsequent measurements.
- Perform an initial rough exploration of the frequency range 50oHz to 30KHz to determine the position of the peak frequency and maximum allowable range of input signal before saturation occurs. Maintain P2 fully clockwise (maximum output level).
- Explore in steps of convenient amplitude the frequency range 500Hz to 30KHz, at constant generator input level. Measure and record at each measuring point the following parameters:
- Frequency
- Input p-p amplitude (sine wave)
- Output p-p amplitude
- Phase shift of the output sine wave over the input one.
The phase shift is only measurable close to the peak, i e. where the output signal is of clearly detectable