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The input attenuator uses a commutating capacitor to cancel the input capacitance of the FET buffer (see DC-10 MHz amp schematic). The commutating capacitors are absolutely necessary to cancel the effect of the input capacitance to the DC-10MHz amplifier. The theory of the commutating capacitors will not be discussed here. The input resistance is 1M ohm at all range settings. All resistances should be chosen to provide 1M ohms at any scale sensitivity. However the ratio of the resistances should also be chosen to provide the scale sensitivities shown below.
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