Why
does the spectrum analyzer block diagram on page 216 use a bandpass filter?
Why
not use a lowpass filter as you did in the example on page 217?
Using
surface acoustic wave (SAW) filters it's possible to design very good
bandpass filters. However,
using SAW filters at low frequencies results in
very large
structures with poor filtering characteristics. The physcial
dimensions of the filters
just become impractical.