What Use Is An F-call?

What use is an F-call? Over the past month or so I've had some limited HF capability at my QTH in the form of a wire loop that runs around the ceiling in my office. It's not pretty and it doesn't really work that well. Across most bands, most of the time, I find an S8 or S9+ noise floor which makes hearing other stations a challenge. I've been at a loss to determine what's going on. I was discussing my plight with some amateurs over lunch one day and someone hit on the idea that I might see if I could determine the source of the noise by way of elimination. So, with that in mind, I plugged my radio into my battery pack, as if I was portable, and then went to the meter box and turned off the house power. Back to the radio and at first I thought the battery had run out, but no, the radio was fine, the battery was at 12.5V and everything was working. One thing was missing, the noise. I used my now quiet radio to have a look across the bands and found all manner of activity. I settled on a CW signal, turned u