Real-time spectrum analyzers address this shortcoming by being able to measure the spectrum with a narrower RBW filter, faster than basic sweeping spectrum analyzers. Figure 1 shows an example of what a LTE signal looks like OTA. In this case the span is set to 40 MHz, which results in a default RBW of 300 kHz. Note that determining the emission in the center of the display is quite difficult. If there was a narrow-band (< 300 kHz) interferer it would be almost impossible to see it with this setup.
Figure 2 shows the same setup using a 1 kHz RBW filter. In this case, it’s clear that the LTE channel and the effective sweep time has only increased to 40 ms. This is one of the first benefits of using a real-time spectrum analyzer (RTSA) to measure interference on the radio channel. Once expensive and desk-bound, a new class of affordable, battery-powered, USB-based real-time spectrum analyzers are now becoming available on the market, making RTSA a practical choice for interference-hunting applications.