Specifications

28 Chapter 3
Measuring a Low−Level Signal
Decreasing the Resolution Bandwidth
Measuring a Low
−
Level Signal
Decreasing the Resolution Bandwidth
Resolution bandwidth settings affect the level of internal noise without
affecting the level of continuous wave (CW) signals. Decreasing the
RBW by a decade reduces the noise floor by 10 dB.
Step 1. Refer to the first procedure “Reducing Input Attenuation” on page 26 of
this chapter and follow steps 1, 2 and 3.
Step 2. Decrease the resolution bandwidth:
Press
BW/Avg, ↓.
The low-level signal appears more clearly because the noise level is
reduced (see Figure 3-3).
Figure 3-3 Decreasing Resolution Bandwidth
A “#” mark appears next to the Res BW annotation in the lower left
corner of the screen, indicating that the resolution bandwidth is
uncoupled.
RBW Selections You can use the step keys to change the RBW in a 1
−3−10 sequence.
For ESA, RBWs below 1 kHz are digital and have a selectivity ratio of
5:1 while RBWs at 1 kHz and higher have a 15:1 selectivity ratio. The
ESA’s maximum RBW is 5 MHz and the minimum is 1 Hz (optional).
All PSA RBWs are digital and have a selectivity ratio of 4.1:1. For PSA,
choosing the next lower RBW for better sensitivity increases the sweep
time by about 10:1 for swept measurements, and about 3:1 for FFT
measurements (within the limits of RBW). Using the knob or keypad,
you can select RBWs from 1 Hz to 3 MHz in approximately 10%
increments, plus 4, 5, 6 and 8 MHz. This enables you to make the trade
off between sweep time and sensitivity with finer resolution.