To add a note regarding quiet conditions,

As I said in an earlier post, the warning type signals which I myself monitor (several types) have been at a very low level lately. They have now disappeared completely. This sometimes happens for a few days after a major earthquake occurs. I have been watching the geomagnetic storm intensity tables lately and they also appear to have been at relatively low levels. That leads me to suspect that those storms could be a source of energy for many of these signals.