National Instruments Toolkit - page 23

© National Instruments Corporation 23 NI Spectral Measurements Toolkit User Guide
Figure9 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. Table1 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
thespectrum
Can distinguish between the two tones in
thespectrum