Resolving Signals of Equal Amplitude Using the Resolution Bandwidth Function
In responding to a
The resolution bandwidth (RES BW) function selects an IF tilter setting for a measurement. Resolution bandwidth is defined as the 3 dB bandwidth of the lilter. The 3 dB bandwidth tells us how close together equal amplitude signals can be and still be distinguished from each other.
Generally, to resolve two signals of equal amplitude, the resolution bandwidth must be less than or equal to the frequency separation of the two signals. If the bandwidth is equal to the separation a dip of approximately 3 dB is seen between the peaks of the two equal signals, and it is clear that more than one signal is present. See Figure
In order to keep the spectrum analyzer calibrated, sweep time is automatically set to a value that is inversely proportional to the square of the resolution bandwidth. So, if the resolution bandwidth is reduced by a factor of 10, the sweep time is increased by a factor of 100 when sweep time and bandwidth settings are coupled. (Sweep time is proportional to l/BW’.) For fastest measurement times, use the widest resolution bandwidth that still permits discrimination of all desired signals. The spectrum analyzer allows you to select from 1 kHz to 3 MHz resolution bandwidth in a 1, 3, 10 sequence, plus 5 MHz, for maximum measurement flexibility.
