Many thanks to SWLing Post contributor, Markku (VA3MK), who notes that Swiss manufacturer Stampfl has introduced the MWS-1 Standing Wave Barrier.
Stampfl notes (translated from German):
A standing wave barrier can improve reception. The standing wave barrier interrupts the ground loop and suppresses the interference caused by the cable shield.
This is designed only to work with receivers (not transmitters) between 0.15 – 30 MHz.
I suppose this might be a form of an RF choke, although I’m sure someone else might know better.
Thank you for the tip, Markku!