It might be only a wire, but...

I decided to listen to 40m WSPR using my SDRPlay RSP1a receiver last night.  It's been a while since I visited that band.

The RSP1a is pretty sensitive, broadly on a par with my FT-450 transceiver.

My antenna for 40m is a half-sloper, fed against a tower at only 6m above ground (I am already 100m above the local area, on a low ridge and steep slopes).

I was pleased, despite this arrangement's simplicity, to be the only northern hemisphere station in 24 hours to hear LU3HO's 5W WSPR signal at 23:44UT (-27dB SNR).

Yet again, the message is simple: environment (position), environment (noise) and environment (ground).