What exactly is the diversity receiver feature in the STD-502-R and STD-503?

There are 2 independent receivers in the STD-502-R/STD-503, each with an antenna spaced a small distance apart from the other. As the diversity extends all the way down to receiver part, we say it has 'diversity receiver'. As the module moves between nulls and peaks due to constructive/destructive interference, the module can select the receiver that outputs valid signal.