Then test the key indicators of digital signal, such as power, MER, BER, etc. When it is necessary to analyze the cause of the fault, we can make a rough judgment with the help of frequency spectrum and constellation diagram. For high-end problems, professional spectrometers are still needed for testing.
The famous manufacturers of field strength instruments in China are Deli in Tianjin, JUSD abroad and Shengli in the United States.