First Venus bounce with the Dwingeloo telescope

On 22 March 2025, we used the Dwingeloo telescope to successfully bounce a radio signal off the surface of Venus. At the time, Venus was in its closest approach to Earth at about 42.000.000 km. Such a conjunction happens when Venus is between the Sun and the Earth, and happens approximately every 580 days.

‘Earth-Venus-Earth’ (EVE) bounces were extensively performed in the 60’s and 70’s to make radar images of Venus. More recently, in 2012, the Arecibo telescope in combination with the Green Bank telescope made a very detailed map of Venus. The first, and only until now, amateur EVE was achieved in 2009 by AMSAT-DL from the 20m Radio telescope at the Bochum Observatory (Sternwarte Bochum).

The Dwingeloo telescope was commanded to transmit a 278 second long tone at a frequency of 1299.5 MHz. Since the light travel time to Venus and back was about 280 seconds, we could receive the reflection of our own signal afterwards. We repeated this cycle four times.

While Dwingeloo received its own echo, the Stockert radio telescope, operated by Astropeiler Stockert e.V., also successfully received Venus’ echo of Dwingeloo’s signals. The receptions in Stockert were stronger than those received in Dwingeloo, since the Stockert receiving chain is a bit more sensitive.

The data analysis consists of correcting the received data for both the expected Doppler shift and the rate of change of this Doppler shift due to the rotations and relative motions of Earth and Venus. After channelizing the received signal in 1 Hz frequency bins, the echo of the transmitted signal should fall exactly in the predicted bin.

The preliminary analysis already shows a 5.4 sigma detection for Dwingeloo-Venus-Dwingeloo, an 8.5 sigma detection for Dwingeloo-Venus-Stockert, and a 9.2 sigma detection when combining the signals of Dwingeloo and Stockert.

We were planning to send complex modulated signals to perform more analysis on the correlations between transmitted and received signals. Unfortunately the transmitter, mounted in Dwingeloo’s focus box for the occasion, started failing after four successful transmissions. We will postpone these other experiments to the next Venus conjunction in October 2026.

In the preparation for this experiment, we collaborated with the Deep Space Exploration Society, who were also preparing an EVE experiment of their own, and the Open Research Institute. During the day of the experiment, we had a lot of help from present CAMRAS volunteers. A big thanks also goes to the volunteers of Astropeiler e.V. for observing with the Stockert telescope.

A technical write-up of this experiment and the data reduction is in the making.

Update 2025-04-01: Raw data for this experiment is now available at https://data.camras.nl/venus/, including an example notebook showing how the reflection of our signal off the surface of Venus can be detected in this data.

Update 2025-05-01: This extra graph shows that the detection was exactly at the expected Doppler and Doppler rate.