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Open-source communications by bouncing signals off the Moon

open.space

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Re: Open-source communications by bouncing signals off the Moon

#71

Post by [deleted] »

mrtnmcc2 wrote: post #23
drmpeg wrote: post #22

Earlier quoted context omitted.

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.

[deleted]

Re: Open-source communications by bouncing signals off the Moon

#72

Post by shakna »

but-vaccum wrote: post #49
shakna wrote: post #40

Earlier quoted context omitted.

Because we're not stationary, and nor is the moon. Latency means greater dispersion, and lower successful return rates.

Latency itself doesn't mean squat. Throw a pair of trancievers into deep space and no relative motion and all bitrate limiting factors (dispersion, multipath, doppler shift- I'm sure there's more) disappear besides SNR/inverse square and retransmission. Going beyond intuition- secondary reasoning says since GSO bandwidth & bitrate is acceptable for TV and sat phones by the hundred. Tercheriary is we have/had a few hu…

... I'd love to see, this particular project, "throw a pair" of tranceivers into deep space.

Re: Open-source communications by bouncing signals off the Moon

#73

Post by kragen »

dreamcompiler wrote: post #62
kragen wrote: post #25

Earlier quoted context omitted.

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…

I didn't see any discussion on your page of the retroreflectors the Apollo astronauts left on the moon. These were put there for distance measuring but they might be useful for laser-based communication too. Caveat: Retroreflectors only reflect in the same direction as the incoming beam. But I'd guess that imperfections in their construction together with the roughly 1 degree of arc spanned by 2 stations on opposite…

1 degree and 54 minutes, it turns out. Amazing when you think about that, isn't it?

Re: Open-source communications by bouncing signals off the Moon

#75

Post by giantg2 »

wjholden wrote: post #68
jmpman wrote: post #51

I’d wondered about using moon bouncing in order to distribute video streaming keys (piracy) in a way which would make it impossible to locate the sender. Unlikely to be viable at scale, as the moon isn’t always visible, but it’s an intriguing covert broadcast mechanism.

Hadn't thought of it from this perspective. An untraceable signal coming from the moon would also be useful for military communications. Electronic warfare and signals intelligence have been powerful tools for both sides in the Ukraine-Russia war.

It's not that untraceable when you have satellites that could pick it up before the bounce.

Re: Open-source communications by bouncing signals off the Moon

#76

Post by giantg2 »

freedomben wrote: post #61
Redster wrote: post #58

Earlier quoted context omitted.

Your location is very very visible to any plane or satellite passing overhead.

Indeed, though it would take some coordination to actually narrow it down precisely. You'd need a few different planes/satellites to detect the signal and share their reading to allow triangulation. With only a single plane or a single satellite that is not in geosynchronous orbit, you could take multiple readings and get a rough idea of location, but the inability to turn from a straight line (not impossible for a p…

Highly directional antennas on a moving platform can perform effectively radio direction finding independently.

Re: Open-source communications by bouncing signals off the Moon

#77

Post by giantg2 »

tatjam wrote: post #50

Haha love this "Not intended for radar applications. Core functionality needed for radar not included due to export control restrictions". Wonder how they prevent usage as radar as this thing could pretty much be a drop-in missile seeker.

The wavelength is suboptimal for that type of tracking/intercept.

Re: Open-source communications by bouncing signals off the Moon

#78

Post by baobrien »

mrtnmcc wrote: post #17
kieranl wrote: post #16

I 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…

What does the RF front end look like? I see the Lattice ECP5, but what are you using to go from bits to waves?

Re: Open-source communications by bouncing signals off the Moon

#79

Post by mrtnmcc »

baobrien wrote: post #78
mrtnmcc wrote: post #17

Earlier 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…

What does the RF front end look like? I see the Lattice ECP5, but what are you using to go from bits to waves?

There are ten 640 MSPS ADCs (I+Q per channel and a cal path, per 4-antenna PCB tile). These are custom MASH ΣΔ designs built from discrete diff pair transistors (cost about $0.08 each) and do noise shaping/decimation to get a clean 50 MHz of baseband bandwidth. The 8x DACs are also ΣΔ, using the LVDS pins of the FPGA and some modulating DSP. Mixers are MAX2850/1, LNA are custom design based on Infineon transistor, and RFPA is a Skyworks part meant for WiFi (have iterated on a few model numbers).

Re: Open-source communications by bouncing signals off the Moon

#80

Post by hdjrnevehhe »

freedomben wrote: post #61
Redster wrote: post #58

Earlier quoted context omitted.

Your location is very very visible to any plane or satellite passing overhead.

Indeed, though it would take some coordination to actually narrow it down precisely. You'd need a few different planes/satellites to detect the signal and share their reading to allow triangulation. With only a single plane or a single satellite that is not in geosynchronous orbit, you could take multiple readings and get a rough idea of location, but the inability to turn from a straight line (not impossible for a p…

Let's remember that there is also a antenna array with LOS yo the mooon.....
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