Daily image
Bouncing radio signals off the planet Venus
© Cees Bassa, Thomas Telkamp, Tammo Jan Dijkema on behalf of CAMRAS
On that date Venus was closest to Earth - still 42 million kilometers away - but close enough to try an unique experiment with the Dwingeloo Telescope; sending a radio signal towards Venus and trying to detect the reflected signal [1]. Since the signal takes 4 minutes and 40 seconds to travel to Venus and back, the Dwingeloo telescope sent a 4 minute, 38 second long signal to Venus and we then recorded data to listen for the reflection with both the Dwingeloo telescope and the Astropeiler Stockert telescope. We did this four times at 10 minute intervals.
The signal we transmitted was a simple tone (carrier wave) at 1299.5 MHz. Though this waveform doesn't allow us to measure the distance to Venus, it does have the useful property that the reflected signal will be contained in a small bandwidth (1-2 Hz), improving the probability of detecting the reflected signals.
This figure shows the combined result of the four recordings of the Dwingeloo and Astropeiler Stockert telescopes [2], where we correct the recorded signal for the predicted line-of-sight velocity (the Doppler frequency) and acceleration (Doppler drift rate) for each telescope to allow integration over the 4 minute 38 second recording and to maximize the signal-to-noise ratio.
The peak in the middle of the plot shows that we detect a ~10 sigma peak at the predicted Doppler frequency and Doppler drift rate, confirming that we detected the reflected signals transmitted by the Dwingeloo telescope.
This technique - using different transmitted waveforms - has been used since the 1960 by the Arecibo and Goldstone telescopes to map the surface of Venus with radar and determine that it rotates only once every 243 days.
[1]: https://www.camras.nl/en/blog/2025/first-venus-bounce-with-the-dwingeloo-telescope/
[2]: https://data.camras.nl/venus/