The space has sounds for those who listen ...

Radio Astronomy

One day - after repeatedly struggling with poor weather conditions - I decided to try a different wavelength. After some tinkering, I finally exclaimed, “Ha! You clouds—now I can see right through you!”

 

My basic setup consists of an SDR radio box and the CubicSDR software running on a MacBook Pro. In addition, I have two antennas, selected specifically for the wavelengths I plan to record. I built them myself.

Straight from the satellite 2026

There are two Russian Earth observation satellites orbiting the Earth in a polar orbit in just over 100 minutes: Meteor M2-3 and Meteor M2-4. They transmit some of their data digitally, but unencrypted, to Earth. If you keep a few things in mind, you can receive and decode the data directly during a flyover. The result is a live image in the visible spectrum.

 

On April 17, 2026, I was able to receive the following image during a 10 minute flyover from 3:17 p.m. to 3:27 p.m. CEST. The transmission frequency of 137.9 MHz was received using a Yagi antenna originally tuned for the GRAVES transmitter and tracked manually. At the farthest points at the beginning and end, the satellite was approximately 3,200 km away, while at its highest point, 88 degrees above the horizon, it was a good 800 km away.

ISS speeding ticket 2025

In the fall of 2025, I built a new Yagi antenna myself. With a gain of 9 dB, it is now possible to detect reflections from the ISS on the GRAVES transmitter frequency during a flyover. The Doppler effect can be used to estimate the ISS’s radial velocity.

 

By comparing these results with the actual orbital data of the ISS, it is possible to verify the accuracy of the measurements. I also wrote a small Python script to calculate the expected frequency shift. It takes into account the current orbital position, the Earth's rotation at the geographical locations of the transmitter and receiver, and, of course, the frequency change that the ISS sees and transmits due to its speed.

 

In an initial test on October 30, 2025, the measured values still differed by around 25%, but a follow-up measurement is planned shortly.

 

meassured doppler effect:

4kHz

 

theoretically:

 

radial velocity GRAVES -> ISS: 6.301 km/s

radial velocity ISS -> Receiver: 4.384 km/s

doppler shift  GRAVES -> ISS: 3006.6 Hz

doppler shift return ISS -> Receiver (based on f1): 2091.9 Hz

 

total doppler shift: 5098.5 Hz

ARISS radio contact with ISS - 1.8.2017

On August 1st, 2017, astronaut Paolo Nespoli spoke with German boy scouts at the VCP-Bundeszeltplatz north of Berlin. During the flyover, the youngsters had the opportunity to ask questions. The video shows a screen recording of SDR software receiving signals on 145.8 MHz in Munich during a thunderstorm. Since only the ISS downlink was recorded, the questions themselves were not captured. For clarity, I later added them as subtitles.

 

ARISS is an international educational outreach program that combines volunteer support and leadership from the AMSAT and IARU communities worldwide with the ISS partner space agencies: NASA, the Russian Space Agency, ESA, JAXA, and CSA.

Meteo Scattering - Perseids 2016

Although not intended to be my first exercise in radio astronomy it turned up to be my first successful one. In August 2016 I used an sdr radio receiver and a small omni-directional discone antenna to observe the climax of the Perseids through heavy clouds and during daytime. The basic idea was to receive the reflections of a strong terrestrial radio source on the ionic trail of the meteors. I tuned in to the frequency of GRAVES in France 460km away. It's a huge radio transmitter with the power of several 10-100kW which I was not able to detect directly. GRAVES is pointed towards the sky and traces satellites and space debris in the earth's orbit. When a meteor hits the atmosphere it heats up very intensely and starts to ionize the air around it. This air operates as a small mirror reflecting the radio waves from the French station back to earth. For a short period of time you can hear the signal and because of the doppler effect the reflected frequency varies with the retarding meteors. This really gives the acustic impression of a falling star. I detected about 45 meteors per hour being about 1/3 of the actual number. This may be the result of limited viewing angle or a limited sensitivity of the system.

compilation of meteor echoes at 143.0478 MHz USB on a 5kHz window. (mp3, 1,4MB)