QRM Eliminator
I built this using a schematic of a X-Phase QRM eliminator I found online. It was a bit involved but with a custom made PCB not so difficult to build.
The basic principle is that you capture noise on a low quality antenna (diversity antenna) and blend it with the signal from your good antenna, with the opposite phase. The circuit lets you tweak the phase shift and magnitude using the three knobs. Using this device is a lot about finding the right settings for the exact frequency you want to receive, and fiddling with the diversity antenna.
It is surprisingly efective. You can also use it for listening to distant AM radio stations by suppressing local noise and signals.
