Every once in a while, I stumble onto something that just makes me think “holy cow, how did they do THAT?”
The most recent is the German AMSAT group ( AMSAT DL) transmitted a signal to Venus and received the reflected signal as it came back to earth.
From the AMSAT (US) web site:
AMSAT-DL Achieves Outstanding Technical First:
Earth-Venus-Earth PathMarburg, 27 March 2009 – On March 25, 2009 the AMSAT-DL team in Germany attained a major milestone in their mission to send a spacecraft to Mars. The team used their mission control station at the IUZ Sternwarte Observatory in Bochum to transmit a radio signal to Venus. After approximately 5 minutes delay and after traveling nearly 100 million kilometers the reflected signal from the surface of Venus was received. This was the first time a German station has received echoes of signals from other planets.
You may be aware that it is a common feat for radio amateurs to bounce signals off the moon and hear the return signal. Hardcore VHF enthusiasts contact each other on the VHF and higher bands by using the moon as a reflector. (Sometimes I kid them that using the moon as a “repeater” is cheating. Of course, it is nothing like that.) This mode is called Earth-Moon-Earth (EME) or simply Moonbounce. The path loss is high, around 250 to 310 dB, so high gain antennas and power amplifiers are required. EME is still on My List of Things to Do and I hope to get around to it someday.
If EME is an accomplishment, then consider the challenge of Earth-Venus-Earth (EVE). The original press release is in German but the information is available in English on the Southgate Amateur Radio Club web page. The signal traveled almost 100 million kilometers which results in a round trip delay of about 5 minutes. This is over 100 times the distance for EME. The frequency used was 2.4 GHz, with an FFT analysis used to pull the signal out of the noise (with an integration time of 5 minutes). I have not seen an analysis of the path loss, so we’ll just use call it ginormous.
Why did AMSAT-DL decide to do this? Well, they want to prove out the feasibility of communications before they launch their spacecraft towards Mars!
73, Bob K0NR