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Abstract

In apparatus for performing frequency response analysis of a system under test to establish response coefficients at various frequencies, a look up Read Only Memory is sequentially addressed to give a driving signal. The signal received from a system under test is fed to the analogue input of a multiplying digital to analogue converter, the digital input being fed from a Read Only Memory, storing values of a reference waveform (e.g., sin wt), by which the received signal is multiplied. The integration period of the multiplying digital to analogue converter is selected such that unwanted multiplication products integrate out, leaving the response coefficient at the reference frequency. For speed, a second channel may be used to establish the orthogonal coefficient. Methods are proposed so that the arrangement operates with single or two quadrant multiplying digital to analogue converters and to select harmonic coefficients.

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