Noise source for transfer function testing

A method of measuring transfer functions of a system under test, the method comprising the steps of:

• a. generating and applying a periodic-random stimulus of period T to the system under test;
• b. measuring the spectrum of the stimulus during a period of T seconds after the stimulus becomes periodic within the desired accuracy;
• c. measuring the spectrum of the response of the system under test after the system response becomes periodic within the desired accuracy during a subsequent period of T seconds starting at a known point relative to the starting point at which the measurement of step b is started;
• d. computing a first estimate of the transfer function of the system under test from the two measured spectrums;
• e. repeating steps a through d to obtain an additional estimate of the transfer function of the system under test using a periodic-random stimulus that is uncorrelated with previous stimuli;
• f. averaging together each additional estimate and the average of the previously obtained estimates of the transfer function of the system under test;
• and
• g. repeating steps e and f a sufficient number of times to obtain an average estimate of the transfer function of the system under test within a selected accuracy.

A method of measuring transfer functions of a system under test, the method comprising the steps of:

• a. generating a finite record length random stimulus;
• b. repeatedly applying the finite record length random stimulus to the system under test;
• c. measuring the spectrums of the stimulus and response of the system under test during identical periods of T seconds in length after the response to the system under test becomes periodic within the desired accuracy;
• d. computing a first estimate of the transfer function of the system under test from the two measured spectrums;
• e. repeating steps a through d to obtain an additional estimate of the transfer function of the system under test using a finite record length random stimulus that is uncorrelated with previous stimuli;
• f. averaging together each additional estimate and the average of the previously obtained estimates of the transfer function of the system under test;
• and
• g. repeating steps e and f a sufficient number of times to obtain an average estimate of the transfer function of the system under test within selected accuracy.

An apparatus for generating a group of periodic random stimuli for application to a system under test, the apparatus comprising:

• random stimulus generator means for generating a finite record length random stimulus of T seconds in length and applying said stimulus to the system under test;
• stimulus storing means responsive to the finite record length random stimulus;
• and
• stimulus repeating means responsive to the stimulus storing means for repeatedly applying the stored finite record length random stimulus of T seconds in length to the system under test a first selected number of times;
• said random stimulus generator means being retriggered a second selected number of times to generate, store and repeat a series of finite record length random stimuli each of T seconds in length and uncorrelated with all other stimuli upon the completion of the repetition of the preceding stimulus.