The plugin will be built only if the [RTLSDR host library](https://github.com/f4exb/librtlsdr) is installed in your system. If you build it from source and install it in a custom location say: `/opt/install/librtlsdr` you will have to add `-DRTLSDR_DIR=/opt/install/librtlsdr` to the cmake command line.
If you want to benefit from the direct sampling you will have to compile and install this library else the RTLSDR library is also provided by many Linux distributions. The SDRangel binary releases are compiled with the direct sampling option.
- Magenta (or pink) square icon: an error occurred. In the case the device was accidentally disconnected you may click on the icon, plug back in and start again.
In device sample rate input mode (7) this is the baseband I/Q sample rate in kS/s. This is the device sample rate (8) divided by the decimation factor (9).
In baseband sample rate input mode (7) this is the device I/Q sample rate in kS/s. This is the baseband sample rate (8) multiplied by the decimation factor (9)
Activates or de-activates the antenna bias tee. Works with v3 dongles only it will be simply ignored by others. It actually activates or de-activates GPIO pin 0 that commands bias tee on v3 dongles.
- if decimation n is 4 or lower: Fc = SR/2^(log2(n)-1). The device center frequency is on the side of the baseband. You need a RF filter bandwidth at least twice the baseband.
- if decimation n is 8 or higher: Fc = SR/n. The device center frequency is half the baseband away from the side of the baseband. You need a RF filter bandwidth at least 3 times the baseband.
This button opens a dialog to set the transverter mode frequency translation options. The details about this dialog can be found [here](../../../sdrgui/gui/transverterdialog.md)
Use this toggle button to switch the sample rate input next (8) between device sample rate and baseband sample rate input. The button shows the current mode:
- **SR**: device sample rate input mode. The baseband sample rate (1.4) is the device sample rate (8) divided by the decimation factor (9).
- **BB**: baseband sample rate input mode. The device sample rate (1.4) is the baseband sample rate (8) multiplied by the decimation factor (9).
<h3>8: Sample rate</h3>
This is the device sample rate or baseband sample rate in samples per second (S/s). The control (7) is used to switch between the two input modes.
The limits are adjusted automatically. In baseband input mode the limits are driven by the decimation factor (9). You may need to increase this decimation factor to be able to reach lower values.
Use the wheels to adjust the sample rate. Left click on a digit sets the cursor position at this digit. Right click on a digit sets all digits on the right to zero. This effectively floors value at the digit position. Wheels are moved with the mousewheel while pointing at the wheel or by selecting the wheel with the left mouse click and using the keyboard arrows. Pressing shift simultaneously moves digit by 5 and pressing control moves it by 2.
The I/Q stream from the RTLSDR ADC is downsampled by a power of two before being sent to the passband. Possible values are increasing powers of two: 1 (no decimation), 2, 4, 8, 16, 32, 64.
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 easily corrected digitally via control (3).
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.
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
