There is a broadband noise source somewhere in the Spencer area that is always there, sometimes in a ‘steady state’ mode and sometimes pulsing at one second intervals, where the center frequency shifts slightly down band and becomes more intense for about 1/2 second at one second intervals. I’ve recorded the sound at 3864 KHz (and saved screenshots from a panadapter) for both the steady state mode and pulsing mode.
Note that the audio spectrum has multiple tones, at 100Hz intervals. Scroll down for several images of the AM audio shown at different zoom levels. Similar noise is even more intense at 3477KHz (and probably exists at other frequencies too).
Steady state noise (not pulsing), 3864 AM:
Noise when pulsing, 3864 AM:
Panadatper screen shots (click any image to view at full size) :
Steady state waterfall and audio spectrum in AM mode, 3864 KHz:
Pulsing waterfall and audio spectrum in AM mode, 3864 KHz:
Similar noise and audio spectrum in AM mode, 3477 KHz:
Audio waveform at different levels of zoom:
Approximately 3 seconds full width
Approximately 0.8 seconds full width
Approximately 0.2 seconds full width