height of the ordinate scale appropriate to the peak of the 

 calibration. Since also, the base of the ordinate scale is zero, 

 the ordinate scale will be completely defined, in terms of the 

 analysis parameters, once the filter bandwidth, is taken into account. 



It should be noted that the application of different filters to 

 the same random signal results in spectra of different apparent sizes 

 (Figure 4), yet the peak values of the calibration will be the same 

 (Figure 7). This results in the same scale far all the spectra in 

 Figure 4, but is not paradoxical so long as it is remembered that 

 the ordinates represent averaging over the filter bandwidth. That 

 is, a 10-cps filter analysis should result in a spectrum which has 

 twice the area of that resulting from a 5-cps filter analysis. 



It has become the practice in the SEADAC to eliminate the 

 confusion resulting from the averaging process by relating the 

 spectral density to a unit frequency band. This is accomplished by 

 dividing the ordinate scale by the "effective bandwidth" ( A f ) 

 defined as 



Af^ = f X k [6] 



where A is the area under the calibration curve (Figure 8) measured 

 in square units of the graph paper, L is the height of the calibration 

 curve measured in units of graph paper, and k is the ratio of any 

 convenient frequency band on the analysis frequency scale to its 

 length in units of graph paper. As an example, consider the area 



21 



