Part 2 of our new occasional series around ‘Fundamental measurement techniques’ takes a look at the basics of spectrum analysis and two types of analyser.
Here we are looking at frequency domain measurements with an analyser which in its most basic form sweeps a filter across a frequency range so providing a graphical display of the spectral content. The spectrum analyser provides a measure of the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals.
The display of a spectrum analyser has frequency on the horizontal axis and amplitude displayed on the vertical axis.
When choosing a spectrum analyser the following specifications are important when making a selection:
To be fully confident in your measurement remember to adjust the measurement procedure for your specific application; test for internal distortion and take sideband noise into account.
Tuned Analysers measure the spectra of electrical signals; dominant frequency; power; distortion; harmonics; bandwidth and other spectral components of a signal in the frequency domain. These parameters are useful in the characterisation of electronic devices, such as wireless transmitters.
Vector signal analysers (VSAs) are also available. VSAs combine sweep methodology with high speed ADCs and other DSP technologies to offer fast, high-resolution spectrum measurements, demodulation, and advanced time-domain analysis. Their primary use is in-channel measurements, such as error vector magnitude and so characterising complex signals such as burst, transient, or modulated signals used in communications, video, broadcast, sonar, and ultrasound imaging applications. VSAs measure the magnitude and phase of the input signal at a single frequency.