The moon is a popular target for ham radio operators to bounce signals since it’s fairly large and follows a predictable path. There are some downsides, though; it’s not always visible from the same point on Earth and is a relatively long way away. Thinking they could trade some distance for size, an amateur radio group from the Netherlands was recently able to use a radio telescope pointed at a geostationary satellite to reflect a signal back down to Earth, using this man-made satellite to complete the path instead of the more common natural one.
While there are plenty of satellites in orbit meant for amateur radio communication (including the International Space Station, although it occasionally does other things too), these all have built-in radio transmitters or repeaters specifically meant for re-transmitting received signals. They’re also generally not in geostationary orbit. So, with a retired radio telescope with a 20-meter dish aimed directly at one of the ones already there, they sent out a signal which bounced off of the physical body of the satellite and then back down where it was received by a station in Switzerland. Of course, the path loss here is fairly extreme as well since the satellite is small compared to the moon and geostationary orbit is a significant distance away, so they used the Q65 mode in WSJT-X which is specifically designed for recovering weak signals.
Don’t break out the tape measure Yagi antenna to try this yourself just yet, though. This path is not quite as reliable as Earth-Moon-Earth for a few reasons the group is not quite sure about yet. Not every satellite they aimed their dish at worked, although they theorize that this might be because of different shapes and sizes of the satellites or that the solar panels were not pointing the correct direction. But they were able to make a few contacts using this method nonetheless, a remarkable achievement they can add to their list which includes receiving a signal from one of the Voyager spacecraft.
Sounds like a 21st-century version of Project Echo, a set of 1960s-era space-balloons that operated as passive reflectors.
Yes, and I remember seeing one of them a few times when I was a youngster in Minnesota. They were quite easily visible with the naked eye.
I was thinking that too. An interesting amateur radio program would be putting 4 “echoes” into geostationary orbit to bounce signals off.
That’s why my starlink signal was degraded last night!
Oh yes , I’m starting my own TWENTY METERS radio telescope antenna to play a little and do some tests
Thinking about this, is there a reason why geostationary communications satellites aren’t just mile-wide spinning foil parabolas? I realise it’s more demanding at the receiver end, but 1kg of space hardware costs like a million times as much as a kg of ground station…
The main reason is power and bandwidth. If you’re only going to power the transmission as it leaves earth you need a lot more power to get a quality signal down to earth again. Generally speaking the weaker the signal the less overall bandwidth you’ll have as you’ll need to include a lot of redundancy to handle signal loss. A 5W FM handheld can give you voice quality output on a powered repeater, where as you need a ton of transmitting and decoding power to get a simple dozen ASCII characters off of a passive repeater.