This YouTube video by Tim Stoddard is a compelling demonstration of how diversity tuning of an SDRplay RSPduo can dramatically reduce the effects of local interference:
There are 2 very practical applications for diversity software. The first is MRC (Maximum Ratio Combination) Diversity which, in order to be effective, needs two antennas presenting the same signal with some degree of diversity. Examples of diversity are:
Spatial Diversity: Using two antennas that are physically separated from one another. Depending upon the expected incidence of the incoming signal, sometimes a space on the order of a wavelength is sufficient. Other times much larger distances are needed – this can be challenging for HF frequencies and below.
Pattern Diversity: Using co-located antennas with different radiation patterns. This type of diversity makes use of directional antennas that are usually physically separated by some (often short) distance. Collectively they are capable of discriminating a large portion of angle space and can provide a higher gain versus a single omnidirectional radiator.
Polarization Diversity: Combining a pair of antennas with orthogonal polarisations. Reflected signals can undergo polarization changes depending on the medium through which they are traveling. A polarization difference of 90° will result in an attenuation factor of up to 34 dB in signal strength. By pairing two complementary polarizations, this scheme can immunize a system from polarization mismatches that would otherwise cause signal fade.
The key thing it to experiment and once you provide some degree of diversity as described above. The “APPLY AUTO” button in SDRuno will select the optimum combination of amplitude and phase to give you an enhanced signal versus either one of the individual signals.
The second application is for local noise cancellation. Here you are using manual control of the phase and amplitude to subtract the unwanted interference from the wanted signal. This is becoming extremely relevant as the sources of electrical interference from power supplies, LED lighting etc proliferate. This is what is demonstrated by Tim Stoddard’s video above. There’s also an SDRplay video explaining more about this if you click here: https://youtu.be/x1DRgprcC6g