On August 11, 2009 at about 0315 UTC I had the first instance of receiving more than one frequency at a time. Others, particularly in the US south east, are reporting this regularly so I suspect I just do not have as good a path to the origin as others might.

The two freqs I could get at this particular time were 7431.2 and 10031.2 kHz. Each frequency consisted of multiple tones about 19.5 Hz apart.

In watching them I noted it seemed that when one was "drifting" down so was the other, possibly in sync. To confirm if they were in sync or not I sampled both signals in one spectral display. They were in sync.

This image is the two freqs fed into Argo. The 10031.2 freq has an intentional +2 Hz offset that I added to separate the two traces. The top trace in each "pair" is the 10031.2 freq, the bottom trace in each "pair" is the 7431.2 kHz freq.

The total sample time of this window is 5 minutes and 40 seconds. During that time the signals experienced a total peak-to-peak deviation of about 56 Hz. For example the trace pointed to with the red arrow peaked at 1249 Hz and bottomed out at 1193 Hz.

As can be seen the two signals mirrored each other essentially perfectly.