Measurement of Weak Signal by Spectrum Analyzer

Scheme Overview

The so-called weak signal is relative to the current state of the spectrum analyzer shows the size of the noise floor. If a signal is measured below the noise floor, the measurement sensitivity of the spectrometer must be increased, I .e., the noise floor of the spectrometer must be reduced.

Application Scenarios

If the input signal is-110dBm, the current state of the spectrometer is shown in Figure 1 below: RBW = 50kHz, input attenuator = 10dBm, input preamplifier is not turned on, and reference level is 0dBm; The displayed noise floor is as high as-75dBm, and the spectrometer cannot measure the input signal below-75dBm. So how to set the spectrum analyzer to observe and measure the small signal of-110dBm? There are 4 parameter settings to reduce the display noise level and improve the measurement sensitivity of the instrument.

If the input signal is less than-110dBm, which is the noise floor shown in Figure 1 below, the spectrometer cannot observe the input signal. If you want to observe the-110dBm signal at this time, how to set the spectrum analyzer? There are 4 parameter settings to reduce the display noise level.

spectrum analyzer

Figure 1 PAS080 spectrum analyzer currently considering noise level up to-75dBm

1. Increase the resolution bandwidth RBW. For every 10-fold reduction in the RBW value, the spectrometer shows a 10dB reduction in the noise floor.
2. Set the reference level to-50dBm.
3. Reduce the spectrometer input attenuator. For every 10dB decrease in the value of the input attenuator, the noise floor of the instrument also decreases by 10dB.
4. Turn on the spectrometer input preamplifier

Set through the above 4 steps. The status parameters of the instrument are shown in Fig. 2, RBW = 1kHz, input attenuator = 0dBm, input preamplifier on, reference level-50dBm, low noise of the spectrum analyzer is about-125dBm, that is, the measurement sensitivity of the instrument is greatly improved compared with the sensitivity shown in the above figure. When the input-110dBm signal, the spectrum analyzer can easily observe and measure this signal, as shown in Figure 2.

The measurement is completed, as shown in Figure 2

spectrum analyzer

Figure 2 After increasing the sensitivity, the small signal is displayed

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