Certain narrow frequency ranges of the HF bands are used by weak-signal experimenters using very slow-speed (QRSS) signaling, often decoded visually.  The most common of these is the 100Hz range from 10,140,000-10,140,100Hz in the 30m band.  This page shows a spectral image of the 30m QRSS band segment as received at W1BW in Concord, MA.

The occasional ~2-minute W-shaped motifs (the "flying W") are my transmissions, sent simultaneously with my WSPR transmissions 200Hz higher. This motif has been recognized as far away as western Austrailia (18km) using only milliwatts of output power.

Images are captured with a modified version of Scott Harden's (AJ4VD) QRSS_VD software running on linux.  Currently using an Icom-703+ transceiver with a 30m delta loop.

I2NDT maintains a compendium of similar grabbers around the world.

Archives of this grabber may be viewed for today and further back in time.