Now THIS is a test pattern. It's the 1800 UTC daily sign-on of NMG, the US Coast Guard in New Orleans, LA. NMG broadcasts a full range of tropical weather products from the NOAA US Tropical Prediction center in four large blocks starting at 0000, 0600, 1200, and 1800 UTC.
A checkered pattern like this can really show what's happening to a fax transmission. There's a little multipath on this one, but mostly we see ionospheric fading, and how different paths fade at different times.
All fax signals are tuned 1.9 kHz lower than their listed frequencies.