Band-pass filters have been used extensively in noise analysis work to obtain power spectra. The approach may be extended for use in frequency response measurements. This may be desirable in some cases where it is possible to use existing equipment or where the filtering inherent in Fourier analysis is inadequate to remove the effect of troublesome background noise. The basic setup consists of two band-pass filters, a multiplier, and an inte­grator. The arrangement is shown in Fig. 4.3. The theoretical development for this method may be found in the work of Kerlin and Ball (4).

Signal 1.

K>—0>

Signal 2_

Fig. 4.3. Band-pass filter analysis circuit.

The frequency analysis requires the use of this setup for the three different pairs of signals shown in Table 4.1. The frequency response is obtained as follows:

Re{G(jco)} = B/A (4.2.1)

Im{ G(co)} = — a>C/A (4.2.2)

This may be repeated for a number of settings for the band-pass filter center frequency to to obtain the complete system frequency response.