This was a Cold War thing to surveil Soviet air defense radars.
Open-source communications by bouncing signals off the Moon
21–30 of 88 posts
Re: Open-source communications by bouncing signals off the Moon
#22I got to see this in person at pacificon a few weeks ago. Also the creator is my friend from UIUC who I consider a brilliant rf/DSP engineer. The demo was able to show and end to end tx chain from gnuradio to a receiver. Really excited to see this! As there are a myriad of other things that this hardware can be used for as well.
Great seeing you at Pacificon! We’re starting with the “Quad” tile — a 4 Tx × 4 Rx SDR designed for arraying — and expect to ship the first units toward the end of this year. They're actually quite capable as a standalone SDR. A Quad can interface directly with a Raspberry Pi 5, and we’ve built a combined enclosure for the SDR + Pi setup. You can run SDR software locally on the Pi or stream IQ samples over gigabit Et…
Will you have arrays with the opposite antenna polarity for point to point links? That is, LHCP (Tx), RHCP (Rx) instead of RHCP (Tx), LHCP (Rx).
Re: Open-source communications by bouncing signals off the Moon
#23Earlier quoted context omitted.
Great seeing you at Pacificon! We’re starting with the “Quad” tile — a 4 Tx × 4 Rx SDR designed for arraying — and expect to ship the first units toward the end of this year. They're actually quite capable as a standalone SDR. A Quad can interface directly with a Raspberry Pi 5, and we’ve built a combined enclosure for the SDR + Pi setup. You can run SDR software locally on the Pi or stream IQ samples over gigabit Et…
Will you have arrays with the opposite antenna polarity for point to point links? That is, LHCP (Tx), RHCP (Rx) instead of RHCP (Tx), LHCP (Rx).
Great question, the latest version has Tx RHCP, and then Rx either LHCP or RHCP controlled with RF switches (in each antenna). This allows point to point links (where the Tx pol and Rx pol should be the same), or "bounce links" where the circular polarization flips with the bounce. I should note RHCP Rx has a bit worse noise figure (LNA is different) but good enough for any line of sight.
Re: Open-source communications by bouncing signals off the Moon
#24I'm skeptical, but how can you not cheer for this? Sounds so awesome.
Have you read Three Body Problem?
Re: Open-source communications by bouncing signals off the Moon
#25If the goal is only to communicate with people on the other side of the world, HF ionosphere skip can do that with cheap 100-year-old technology (although transistors make it easier). I assume the goal is to do something cooler than that.
The entire HF band, including the parts already used for something, is only 27 MHz of bandwidth, it's full of noise, and at any given time only a fraction of it can propagate to the other side of the world, dependent on time of day and, literally, sunspots. This antenna has 1100 MHz of bandwidth, the analog front end has 40 MHz for any given conversation, and noise levels are much lower. It could conceivably deliver Shannon bit rates one or more orders of magnitude higher. But it only works when the moon is visible to both sides of the connection.
I discussed these possibilities and some more challenging ones in 02013 in https://dercuano.github.io/notes/ultraslow-radio.html, although I was considering laser moonbounce rather than phased-array microwave moonbounce because of the higher antenna gain available.
Re: Open-source communications by bouncing signals off the Moon
#26If the goal is only to communicate with people on the other side of the world, HF ionosphere skip can do that with cheap 100-year-old technology (although transistors make it easier). I assume the goal is to do something cooler than that.
> I assume the goal is to do something cooler than that. Yes. Bounce the signal off the moon. The moon .
What if we tried more power?
Re: Open-source communications by bouncing signals off the Moon
#27For someone not well versed with the terminology, can someone please tell what kind of bitrate this can provide? In bytes per second.
Re: Open-source communications by bouncing signals off the Moon
#28Latency?
I'm more interested in bitrate.
Re: Open-source communications by bouncing signals off the Moon
#29For someone not well versed with the terminology, can someone please tell what kind of bitrate this can provide? In bytes per second.
It's not even a byte per second. The latency of the distances involved mean you're looking at around two seconds per round trip, plus a little extra because of the fuzziness of radio in space and absolutely everything that can distort it.
There's a lot of math that goes into selecting the right bit-width for the signal, which I ain't doing here and now [0], but most 24dB things tend to be 32bit for reasons. The arrays here are a bit more, but probably fit that kind of channel.
Assuming 32bit and 30dBi, you'd be sending at roughly 20-30MHz, and receiving at about 1kHz. (Less if you hit bad weather.)
So... 1 bit per second. Not byte. Bit.
Re: Open-source communications by bouncing signals off the Moon
#30For someone not well versed with the terminology, can someone please tell what kind of bitrate this can provide? In bytes per second.
It's not even a byte per second. The latency of the distances involved mean you're looking at around two seconds per round trip, plus a little extra because of the fuzziness of radio in space and absolutely everything that can distort it. There's a lot of math that goes into selecting the right bit-width for the signal, which I ain't doing here and now [0], but most 24dB things tend to be 32bit for reasons. The array…
Thank you so much. Are these rough calculations based on the smallest (quad), mini or the large array?