A year with a yagi

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Next to the Dwingeloo Telescope, a yagi antenna continuously observes the skies in the 2m-band. It is pointed toward South, to catch meteor reflections of terrestrial narrow-band signals around 140 MHz. Amateur meteor observers use these reflections to count the activity of meteor showers.

For the last year, we archived some of the waterfall plots from this antenna. They are reduced in size that everything except the background noise is invisible. But the background noise also shows some interesting features. The plots are arranged by date (horizontal) and UTC time (vertical). What we can learn from these plots:

• Some days, the system was switched off (black patches).
• The system was restarted a few times, and the overall sensitivity was changed.
• In some periods, there was increased radio interference. This could be due to activities on the test field related to the Dwingeloo Test Station, but there may also be other explanations.

The most interesting feature however, is the diagonal band. An increased brightness seen around 18h in September 2021 appears about four minutes earlier every day. Indeed, this is radio emission from the Galactic plane, which crosses the field of view of the antenna.

It may have been with a plot like this that Karl Jansky discovered radio astronomy. If only we had made this plot in 1930...