Making Basic Measurements Using Spectrum Analyzer Mode

Measuring low-level Signals Using Attenuation, Video Bandwidth, and Video Averaging

Example: The video-filter control is useful for noise measurements and observation of low-level signals close to the noise floor. The video filter is a post-detection low-pass filter that smooths the displayed trace. When signal responses near the noise level of the spectrum analyzer are visually masked by the noise, the video filter can be narrowed to smooth this noise and improve the visibility of the signal. (Reducing video bandwidths requires slower sweep times to keep the spectrum analyzer calibrated.)

Using the video bandwidth function, measure the amplitude of a low-level signal.

1.As in the first example, connect an antenna to the spectrum analyzer input. Set the spectrum analyzer to view a low-level signal.

2.Narrow the video bandwidth by pressing m, VID BW AUTO MAN , and the step-down key ((7J-J). This clarifies the signal by smoothing the noise, which allows better measurement of the signal amplitude.

A “#” mark appears next to the VBW annotation at the bottom of the screen, indicating that the video bandwidth is not coupled to the resolution bandwidth.

Instrument preset conditions couple the video bandwidth to the resolution bandwidth so that the video bandwidth is equal to or narrower than

the resolution bandwidth. If the bandwidths are uncoupled when video bandwidth is the active function, pressing VID BW AUTO MAN (so that AUTO is underlined) recouples the bandwidths. See Figure 4-18.

4-26