G3ZIL's blog

The gap of about 9 s between the ends of WSPR transmissions and the start of the next enables noise level estimates within the 1400-1600Hz audio band that can be used with a passive software-controlled switched delay-line, attenuator and combiner system to provide very useful noise cancellation.

An outline of the approach together with examples of the noise cancellation achieved at G3ZIL on 40m using a pair of inverted V dipoles with their apexes at just 5m is provided in the following pdf.