Update documentation according to new DC and IQ correction implementation

plugins/samplesource/airspyhf/readme.md

@@ -47,15 +47,13 @@ Baseband I/Q sample rate in kS/s. This is the device to host sample rate (3) div
 
 <h3>2: Lo ppm correction</h3>
 
-This is the correction factor in ppm applied to the local oscillator. The Airspy HF LO has 1 kHz increments so anything in between is obtained by mixing the signal with a Hz precision NCO. This is actually done in the AirspyHF library.
+This is the correction factor in ppm applied to the local oscillator. The Airspy HF LO has 1 kHz increments so anything in between is obtained by mixing the signal with a software NCO. This is actually done in the AirspyHF library.
-
-On HF band the LO correction is not necessary because the LO is largely precise enough for the frequencies involved. You can disable the NCO in AirspyHF library by setting the value to zero. Since the LO control in SDRangel has a 1 kHz step the NCO correction will always be zero. In AirspyHF library (my fork) the NCO is not active (no extra complex multiplication) if the correction is zero. On HF band it is recommended not to use the LO correction (set it or leave it at 0). 
 
 You can reset the ppm value anytime by pressing on button (3)
 
 <h3>3: Reset LO ppm correction</h3>
 
-THis resets the LO ppm correction (zero the value). By doing so the LO trimming NCO in AirspyHF libray is disabled.
+This resets the LO ppm correction (zero the value).
 
 <h3>4: Band select</h3>
 
@@ -66,7 +64,7 @@ Use this combo box to select the HF or VHF range. This will set the limits of th
 
 <h3>5: Device to hast sample rate</h3>
 
-This is the device to host sample rate in samples per second (S/s).
+This is the device to host sample rate in kilo samples per second (kS/s).
 
 Although the combo box is there to present a choice of sample rates at present the AirspyHF+ deals only with 768 kS/s. However the support library has provision to get a list of sample rates from the device incase of future developments.
 

plugins/samplesource/bladerfinput/readme.md

@@ -43,7 +43,7 @@ Baseband I/Q sample rate in kS/s. This is the device sample rate (4) divided by
 These buttons control the local DSP auto correction options:
 
   - **DC**: auto remove DC component
-  - **IQ**: auto make I/Q balance
+  - **IQ**: auto make I/Q balance. The DC correction must be enabled for this to be effective.
   
 <h3>3: XB-200 add-on control</h3>
 

plugins/samplesource/hackrfinput/readme.md

@@ -51,7 +51,7 @@ Use this slider to adjust LO correction in ppm. It can be varied from -10.0 to 1
 These buttons control the local DSP auto correction options:
 
   - **DC**: auto remove DC component
-  - **IQ**: auto make I/Q balance
+  - **IQ**: auto make I/Q balance. The DC correction must be enabled for this to be effective.
 
 <h3>3A: Link Tx frequency</h3>
 

plugins/samplesource/limesdrinput/readme.md

@@ -93,7 +93,7 @@ Enables or disables the auto remove DC component
 
 <h4>2.5: I/Q balance auto correction</h4>
 
-Enables or disables the auto I/Q balance correction
+Enables or disables the auto I/Q balance correction. The DC correction must be enabled for this to be effective.
 
 <h4>2.6: External clock control</h4>
 

plugins/samplesource/plutosdrinput/readme.md

@@ -68,7 +68,7 @@ Use this slider to adjust LO correction in ppm. It can be varied from -20.0 to 2
 These buttons control the software DSP auto correction options:
 
   - **DC**: (6) auto remove DC component
-  - **IQ**: (7) auto make I/Q balance
+  - **IQ**: (7) auto make I/Q balance. The DC correction must be enabled for this to be effective.
 
 ☞ AD9363 has a good hardware DC and I/Q compensation so there should not be a use for this software auto-correction.
   

plugins/samplesource/rtlsdr/readme.md

@@ -47,7 +47,7 @@ This is the correction to be applied to the local oscillator in ppm.
 These buttons control the local DSP auto correction options:
 
   - **DC**: auto remove DC component
-  - **IQ**: auto make I/Q balance
+  - **IQ**: auto make I/Q balance. The DC correction must be enabled for this to be effective.
   
 <h3>4: Baseband center frequency position relative the center frequency</h3>
 

plugins/samplesource/sdrplay/readme.md

@@ -26,7 +26,7 @@ This is the correction in tenths of ppm steps. This is hardly useful with SDRpla
 
 <h3>3. DC and IQ imbalance correction</h3>
 
-These controls are also common with many source plugins. IQ imbalance is hardly useful but SDRplay is affected by DC bias when used at zero IF.
+These controls are also common with many source plugins. IQ imbalance is hardly useful but SDRplay is affected by DC bias when used at zero IF. Note that the DC correction must be enabled for the I/Q correction to be effective.
 
 <h3>4. Band selection</h3>
 

plugins/samplesource/testsource/readme.md

@@ -41,7 +41,7 @@ Baseband I/Q sample rate in kS/s. This is the device to host sample rate (3) div
 These buttons control the local DSP auto correction options:
 
   - **DC**: auto remove DC component
-  - **IQ**: auto make I/Q balance
+  - **IQ**: auto make I/Q balance. The DC correction must be enabled for this to be effective.
 
 <h3>3: Carrier shift from center frequency</h3>