Pioneer 10 signal
Once again we are using the signal from Pioneer 10 as an end-to-end test of our system. At a distance of more than 10,000,000,000 km, its 8 Watt transmitter produces a signal that has many of the characteristics of a signal from another planetary system. It is a coherent narrowband signal with a modest frequency drift rate (caused by the Earth's rotation). It is ideal for test purposes since it is relatively strong and easily seen on the "waterfall" plot as shown below.
This plot shows the power in 924 channels over time. Each horizontal row of dots gives a snapshot of the amount of power in each of the channels at a specific time. The larger the dot, the more power in that channel. Every 0.7 seconds a new row of dots is added. Over about two minutes the picture shown above builds up. If a particular channel always had a signal in it, we would see a vertical line since that channel would always have a more power than the other channels, and so would tend to have larger than average dots. The signal from Pioneer 10 drifts in frequency and so moves from channel to channel over time. It can be seen as a line beginning at the lower right edge of the plot.