Editing Spectrum analyzer (section)

==== Minimum signal detection time ====
This is related to the sampling rate of the analyser and the [[Fast Fourier transform|FFT]] rate.  It is also important for the realtime spectrum analyzer to give good level accuracy.

Example: for an analyser with {{nowrap|40 MHz}} of realtime [[Bandwidth (signal processing)|bandwidth]] (the maximum RF span that can be processed in realtime) approximately {{nowrap|50 Msample/second}} (complex) are needed.  If the spectrum analyzer produces {{nowrap|250 000 FFT/s}} an FFT calculation is produced every {{nowrap|4 μs.}}  For a {{nowrap|1024 point}} FFT a full spectrum is produced {{nowrap|1024 x (1/50 x 10<sup>6</sup>),}} approximately every {{nowrap|20 μs.}}  This also gives us our overlap rate of 80% (20 μs − 4 μs) / 20 μs = 80%.

[[Image:Comparison of Max Hold Spectrum Analyzer trace and Persistence Trace.png|thumb|left|400px|Comparison between Swept Max Hold and Realtime Persistence displays]]

===== Persistence =====
Realtime spectrum analyzers are able to produce much more information for users to examine the frequency spectrum in more detail. A normal swept spectrum analyzer would produce max peak, min peak displays for example but a realtime spectrum analyzer is able to plot all calculated FFT's over a given period of time with the added colour-coding which represents how often a signal appears. For example, this image shows the difference between how a spectrum is displayed in a normal swept spectrum view and using a "Persistence" view on a realtime spectrum analyzer.

[[Image:Bluetooth signal behind wireless lan signal.png|thumb|right|350px|Bluetooth signal hidden behind wireless LAN signal]]

===== Hidden signals =====
Realtime spectrum analyzers are able to see signals hidden behind other signals. This is possible because no information is missed and the display to the user is the output of FFT calculations. An example of this can be seen on the right.