National Instruments NI Spectral Measurements Toolkit - Manual (Page 23)

© National Instruments Corporation 23 NI Spectral Measurements Toolkit User Guide
Figure 9 shows the spectrum of a multitone signal calculated using
two RBW values. The multitone signal consists of two tones, at frequencies
1.0 MHz and 1.1 MHz, separated by 100 kHz. Table 1 shows the trade-offs
of using two different RBWs.
Note An RBW of 103.5 kHz is not sufficient to distinguish between two tones that
are 100 kHz apart.
Figure 9. RBW Example
Table 1. Larger versus Smaller RBW
Larger RBW (103.5 kHz) Smaller RBW (9.94 kHz)
Smaller FFT size, requiring less computation
time Larger FFT size, requiring more computation
time
Cannot distinguish between the two tones in
the spectrum Can distinguish between the two tones in
the spectrum