Spectrum Analyzer Introduction
Just like an oscilloscope is used to measure and view an electronic signal versus time, a spectrum analyzer is used to measure and view an electronic signal versus frequency.
The main specification points for a spectrum analyzer are its frequency range, the measurement resolution in this frequency range and the signal signal levels that can be displayed.
The three important signal levels are:
- Maximum level that can be input to the spectrum analyzer without damaging the spectrum analyzer.
- Spur free maximum level is the maximum input signal to stay below for a clean, spur free display.
- Noise level is the lowest discernable signal level and this depends on the resolution bandwidth. A lower bandwidth gives a lower noise level.
The maximum input signal level for the tinySA is 10dBm. Signals below -30dBm should not generate spurs in low input mode and the noise level with an Resolution Bandwidth RBW of 10kHz is about -105dBm.
More expensive spectrum analyzers can digitize a broad frequency range at once and,using FFT, calculate the signal over a broad frequency range. Spectrum analyzers like the tinySA use a resolution filter that is used to isolate the input power in a small frequency range. This resolution filter is swept across the desired frequency range. As the oscillator that does the sweeping and the power detector that measures the signal power require some settling time the scanning speed of the tinySA is limited. The narrower the filter the more time is needed to settle. The fastest scanning speed occurs with an RBW or 300kHz or wider and is about 2 scans per second. But with increase of the frequency span and decrease of the RBW the scanning speed decreases quickly.
A scan from 0 MHz to 350 MHz with an RBW of 10 kHz takes about 2 minutes.