picked too large, the power per division on the # axis as shown 
in equation (10.34) can have other values of power from other 
parts of the # axis aliased into (or added into) the true values 
for the particular band desired. 
Consider the sketch at the top of Plate LI. If only the four 
values labeled 1, 2, 3, and 4 are given, it is not possible to 
tell the difference between the dashed sine curve and the solid 
sine curve. In fact, since the numerical method of analysis assigns 
all of the power present to spectral values between zero and 
27/2 At, if the solid curve represents a spectral value greater 
than 27/2 At, it will be aliased by the method of analysis into 
a spectral value associated with the dashed curve on the plate. 
These features are explained in greater detail by the values shown 
in (10.38). The spectral frequency given by 2rh/2 Atm for h equal 
to zero, one, two....through m has aliases given by (27/2 At) + 
(2rh/2 Atm), (47/2 At) + (2rh/2 Atm), (67/2 At) + (2rh/2 Atm) 
and so forth. From the little table it is seen that the value 
of the aliased cosine terms is the same at the points t = 0, 
Ne 2At.....as the value of the true component at these points. 
The sketch Daaloe shows this effect in another way. The power 
associated with the first little black strip shows up in that 
range of the spectrum upon analysis, but if there is any power 
associated with the other little black strips, it will show up 
in the range where the true values occur. 
The important point is to pick At small enough so that 
there is no appreciable power in the power spectrum for spectral 
frequencies above 27/2At. Stated another way, components with 
- 278 - 
