Pure Signal is the name given to the theory and implementation of the clean transmission logic developed by the OpenHPSDR team and implemented in PowerSDR as used with the ANAN radios. You often see some truly rotten signals on the air, an example is shown below. As a good operator you do not want a signal like this!
Note: at present the pure signal correction is not applied, only the diagnostic information is shown.
The same concept is used in the SDR Console although the implementation is developed from the ground up using the data returned by the radio when in transmit mode. Looking at the images below, in receive mode only the modulation signal is show but in transmit mode both the drive and output (as measured at the antenna) are shown.
When both the drive applied to the Digital-to-analog converter (DAC) and the output as measured at the antenna are known it is possible to modify the drive so that the output is as clean as possible.
Drive and Output (Transmit)
The information required to actually perform the pure signal correction is the drive vs output amplitude and phase. In the two images below we see that the amplitude gain is not linear - there is more gain at lower levels. It is this information which is used in the feedback loop to adjust the drive gain at different levels.