18 Chapter 1
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
Resolving Small Signals Hidden by Large Signals
When dealing with the resolution of signals that are close together and
not equal in amplitude, you must consider the shape of the IF filter of
the analyzer, as well as its 3 dB bandwidth. (See “Resolvin g Signals of
Equal Amplitude” on page 14 for more information.) The shape of a
filter is defined by the selectivity, which is the ratio of the 60dB
bandwidth to the 3 dB bandwidth. (Generally, the IF filters in this
analyzer have shape factors of 15:1 or less for resolution bandwidths
≥1kHz and 5:1 or less for resolution bandwidths ≤ 300 Hz). If a sma ll
signal is too close to a larger signal, the smal ler signal can be hidden by
the skirt of the larger signal. To v iew the smaller s ignal, you mu st select
a resolution bandwidth such that the separation between the two
signals (a) is greater than half the filter width of the larger signal (k)
measured at the amplitude level of the smaller signal. See Figure1-8.
Figure 1-8 Resolution Bandwidth Requirements for Resolving Sm a ll
Signals