Why do I always go wrong with my spectrum analyzer?

 

    1. Frequency scanning range:

 

    The upper and lower limits of the spectrum analyzer's scanning frequency are specified. By adjusting the scanning frequency range, you can make detailed observations of the frequencies of interest. The wider the scanning frequency range, the longer it takes to scan once, and the lower the measurement accuracy of each point on the spectrum. Therefore, if possible, try to use a smaller frequency range. When setting this parameter, you can determine it by setting the scanning start frequency and stop frequency, for example: startfrequency=1MHz,stopfrequency=11MHz. You can also determine it by setting the scanning center frequency and frequency range, for example: centerfrequency=6MHz,span=10MHz. The results of these two settings are the same.

 

    2. IF resolution bandwidth:

 

    The intermediate frequency bandwidth of the spectrum analyzer is specified. This indicator determines the selectivity and scanning time of the instrument. Adjusting the resolution bandwidth can achieve two purposes. One is to improve the selectivity of the instrument so that two signals with close frequencies can be distinguished. The other purpose is to improve the sensitivity of the instrument. Because any circuit has thermal noise, this noise will drown out weak signals and make the instrument unable to observe weak signals. The amplitude of the noise is proportional to the bandwidth of the instrument. The wider the bandwidth, the greater the noise. Therefore, reducing the resolution bandwidth of the instrument can reduce the noise of the instrument itself, thereby enhancing the detection ability of weak signals.

 

    The resolution bandwidth is generally expressed as a 3dB bandwidth. When the resolution bandwidth changes, the signal amplitude displayed on the screen may change. If the bandwidth of the measured signal is greater than the passband bandwidth, then when the bandwidth increases, the displayed amplitude will increase due to the increase in the total energy of the signal passing through the intermediate frequency amplifier. If the bandwidth of the measured signal is less than the passband bandwidth, such as for a signal with a single spectrum line, the amplitude of the displayed signal will not change regardless of how the resolution bandwidth changes. A signal whose signal bandwidth exceeds the intermediate frequency bandwidth is called a broadband signal, and a signal whose signal bandwidth is less than the intermediate frequency bandwidth is called a narrowband signal. The interference source can be effectively located based on whether the signal is a broadband signal or a narrowband signal.

 

    3. Scanning time:

 

    The time it takes for the signal received by the instrument to scan from the lowest end to the highest end of the scanning frequency range is called the scanning time. The scanning time matches the scanning frequency range. If the scanning time is too short, the measured signal amplitude is smaller than the actual signal amplitude.

 

    4. Video bandwidth:

 

    The function of video bandwidth is the same as that of intermediate frequency bandwidth, which can reduce the in-band noise of the instrument itself, thereby improving the instrument's ability to detect weak signals.