Added manual for Power spectral density spectrums chart

docs/wiki/guides/current/BBE-Power-Spectral-Density-charts.md

@@ -0,0 +1,64 @@
+# Blackbox Explorer Power spectral density charts
+
+The Blackbox Explorers spectrum analyser can show power spectral density (PSD) charts
+![image](/img/blackbox/psd_1.jpg)
+
+The power spectral density charts show the noises level in standard dBm/Hz units.
+For example: 
+- every 10dBm values difference mean the noise power relation as 10, 20dBm as 100, 30dBm as 1000
+- every 20dBm values difference mean the noise amplitude relation as 10, 40dBm as 100, 80dBm as 1000
+
+## The "Power spectral density" spectrum chart
+
+It shows the noises power spectral density by frequency.
+![image](/img/blackbox/psd_2.jpg)
+The vertical slider can change curves smooth. The less smooth curve has more frequency resolution.
+![image](/img/blackbox/psd_3.jpg)
+The mouse cursor shows current power values by pressing Shift key 
+![image](/img/blackbox/psd_4.jpg)
+
+## The power spectral density by RPM heat map diagram ("PSD vs RPM")
+
+It shows the noise power spectral density by frequency and RPM.
+![image](/img/blackbox/psd_5.jpg)
+It has the next settings by using the three number input fields in the right-up charts corner:
+- "Max dBm" - to set maximum power level what is showed as white color at the chart
+- "Min dBm" - to set minimum power level what is showed as black color at the chart
+- "Limit dBm" - the power values what are less this limit are showed as black
+
+The mouse cursor shows current power values by pressing Shift key 
+![image](/img/blackbox/psd_6.jpg)
+
+## The power spectral density by throttle heat map diagram  ("PSD vs Throttle")
+
+It shows the noises power spectral density by frequency and throttle.
+It looks like power spectral density by RPM. 
+But the power spectral density by RPM is more helpfull, when the RPM filter works.
+![image](/img/blackbox/psd_7.jpg)
+
+
+# <a name="spectrum_comparison">Blackbox Explorer: Power spectral density curves comparison</a>
+
+It possible to compare several spectrums by using of power spectral density spectrum chart.
+It possible to compare up to 6 spectrums.
+
+To compare PSD spectrums for one log file curves:
+- to show "Power spectral density" chart for curve
+- to select several curves by Ctrl + Mouse click at the curves legend
+- to analyse spectrums difference
+- to press "Clr" button to remove the all compared curves
+- to repeate Ctr + Mouse click at some curve to remove it from comparison
+![image](/img/blackbox/psd_8.jpg)
+
+To compare PSD spectrums for different log file curves:
+- to show "Power spectral density" for the first log file curve
+- to press "Exp" (Export) button. The spectrum data will exported to .CSV file
+- to export spectrums from some log files what you need for comparison 
+- to show "Power spectral density" to compare some curve with other
+- to press "Imp" (Import) button. To select several exported curves log files for comparison by using Open file dialog
+- the sepctrums will showed at one chart for analyses
+![image](/img/blackbox/psd_9.jpg)
+![image](/img/blackbox/psd_10.jpg)
+
+The legends width and position can set in User settings dialog box
+![image](/img/blackbox/psd_11.jpg)

docs/wiki/guides/current/Black-Box-logging-and-usage.md

@@ -42,6 +42,8 @@ Do click on all the buttons to learn what they do and '?' for the Keyboard Short
 #### Betaflight blackbox explorer Version 3.7
 
 [Blackbox Explorer MinMax control](/docs/wiki/guides/current/BBE-MinMax-control-manual)
+[Blackbox Explorer: Power spectral density spectrums charts](/docs/wiki/guides/current/BBE-Power-Spectral-Density-charts)
+[Blackbox Explorer: Power spectral density spectrums comparison](/docs/wiki/guides/current/BBE-Power-Spectral-Density-charts#spectrum_comparison)
 
 ### How to obtain data to evaluate noise frequency for setting the Notch filter.