• Switch on the power supply.
• Set up a signal generator to have a sinusoidal output of 1 volt peak-to-peak
and a frequency of approximately 455kHz, then connect it to the input socket
of the Detuned Resonant Circuit (tp35).
• Use your double-beamed oscilloscope to monitor the output from the
transformer’s secondary winding tp39, together with the input signal to the
detector at tp35. Use tp35 to trigger the oscilloscope.
• Vary the frequency output of the signal generator either side of the present
position and note that the amplitude of the signal at tp39 follows the
frequency response shown in Figure 98.
• Monitor the detector’s output signal at tp4O together with the input signal to
the detector at tp35. Again use tp35 to trigger the oscilloscope.
• Vary the frequency of the signal generator’s output around 455kHz and see
that the DC voltage level also follows the response curve in Figure 98.
8.4a Enter the maximum DC voltage level measured at tp4O (in volts).
• If you have access to a frequency meter, record the DC voltage at tp4O for
incoming frequencies from 2OkFlz below to 20kHz above the resonance
frequency of the tuned circuit.
• Plot the DC voltage at tp4O against frequency and check that the response is
similar to that shown in Figure 98.
• Carefully adjust the signal generator to provide the carrier frequency of
455kHz. By making very small adjustments whilst monitoring the DC
voltage at tp4O, check that this frequency occurs approximately halfway up
the left-hand slope of the response. If it does not, it may be that T4 needs
adjusting. To do this, follow the instructions given in Appendix 1
‘Adjustment of Tuned Circuits’.
• Disconnect the signal generator.