54 Chapter2
Making Measurements
Example 1: Resolving Closely Spaced Signals (with Resolution Bandwidth)
Figure 2-3 Bandwidth Shape Factor
Use a 100 kHz resolution bandwidth filter to resolve this third-order
intermodulation distortion product. The 100 kHz filter has a typical
shape factor of 12:1, a 60 dB bandwidth of 1.2 MHz, and a
half-bandwidth value of 600 kHz. This half-bandwidth is narrower than
the frequency separation, so the two input signals will be resolved. See
Figure 2-4.
However, using a 300 kHz filter, the 60 dB bandwidth is 3.6 MHz and
the half-bandwidth value is 1.8 MHz. Since this half-bandwidth is
wider than the frequency separation, the signals most likely would not
be resolved
• Change the resolution bandwidth to 300 kHz and notice that you can
no longer see that the distortion product is present. See Figure 2-5
on page 55.
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