RTLSDR: offset tuning documentation

plugins/samplesource/rtlsdr/readme.md

@@ -109,11 +109,15 @@ The I/Q stream from the RTLSDR ADC is downsampled by a power of two before being
 
 Use this checkbox to activate the special RTLSDR direct sampling. This can be used to tune to HF frequencies.
 
-<h3>9: RF bandwidth</h3>
+<h3>9: Offset tuning</h3>
+
+This controls the offset tuning. Some RF frontends like the obsolete E4000 implement this feature and it can seriously reduce the central DC peak without digital correction. This does not work for the R820T and R820T2 that are very popular on which it will produce no effect. However these RF frontends exhibit a central DC peak much smaller than on the E4000 and can be easly corrected digitally via control (3).
+
+<h3>10: RF bandwidth</h3>
 
 This controls the tuner filter bandwidth and can be varied from 350 kHz to 8 MHz. In practice depending on the value this appears to be larger and the filter center is slightly offset above the center frequency. This can still be very useful to eliminate or attenuate large signals outside the device to host I/Q stream passband.
 
-<h3>10: RF gain and AGC</h2>
+<h3>11: RF gain and AGC</h2>
 
 The slider sets RF gain in dB. The values are defined in the RTLSDR device and generally are: 0.0, 0.9, 1.4, 2.7, 3.7, 7.7, 8.7, 12.5, 14.4, 15.7, 16.6, 19.7, 20.7, 22.9, 25.4, 28.0, 29.7, 32.8, 33.8, 36.4, 37.2, 38.6, 40.2, 42.1, 43.4, 43.9, 44.5, 48.0, 49.6
 

plugins/samplesource/rtlsdr/rtlsdrplugin.cpp

@@ -14,7 +14,7 @@
 
 const PluginDescriptor RTLSDRPlugin::m_pluginDescriptor = {
 	QString("RTL-SDR Input"),
-	QString("4.0.6"),
+	QString("4.3.1"),
 	QString("(c) Edouard Griffiths, F4EXB"),
 	QString("https://github.com/f4exb/sdrangel"),
 	true,