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Open-source communications by bouncing signals off the Moon

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

#61

Post by freedomben »

Redster wrote: post #58
npsomaratna wrote: post #56

Earlier quoted context omitted.

I have no understanding of the physics involved, but could the broadcast location be reverse engineered? (With triangulation and clever math?)

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 plane of course, but it would require intentionality and willingness for the crew/commanders and typically not cheap as it disrupts whatever flight plan they previously had) would be a hindrance. That said, with how many satellites are up there I doubt it would take much extra effort to do that coordination if the satellite operators have motivation to do so.

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

#62

Post by dreamcompiler »

kragen wrote: post #25
dreamcompiler wrote: post #19

If 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…

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 sides of the earth might make this idea practical with a better S/N than using only the lunar surface as a reflector. But I don't know. They might be a lot more precise than 1 degree.

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

#63

Post by [deleted] »

ErroneousBosh wrote: post #52
topspin wrote: post #45

Earlier quoted context omitted.

Hams bounce signals off of everything. Aircraft scatter, for example. Probably the coolest is using the ion trails of meteorites. When meteors punch through the atmosphere, they create ionized trails. These trails can reflect RF signals. Some of these happen to be optimal at low VFH frequencies, and hams make contacts using frequencies that ordinarily don't work beyond line of sight.

We've bounced 2.4GHz signals off Venus. Venus .

[deleted]

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

#65

Post by Polizeiposaune »

gus_massa wrote: post #2

I started reading thinking it was impossible but it has been done with other devices https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Ear...

The big dish antenna at Stanford University (visible from I-280) was, among many other things, used to monitor Soviet radar signals from Sary Shagan in Kazakhstan, that bounced off the moon some of the time.

The wikipedia article:

https://en.wikipedia.org/wiki/Stanford_Dish

links to:

https://web.archive.org/web/20201108114110/https://www.cia.g...

which has this tidbit which explains why it works as well as it does when it works:

"Fortunately for us, the moon appears only slightly rough to radio waves; most of the reflected energy comes back from an area at the near point just a few miles in diameter. The bulk of the energy striking farther around on the side is reflected out into space and never returns to earth."

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

#67

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…

Hey, thanks!

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

#68

Post by wjholden »

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.

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

#69

Post by dreamcompiler »

kragen wrote: post #67
dreamcompiler wrote: post #62

Earlier quoted context omitted.

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…

Hey, thanks!

https://en.wikipedia.org/wiki/List_of_retroreflectors_on_the...

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

#70

Post by mschuster91 »

cactacea wrote: post #8
jacquesm wrote: post #6

Earlier quoted context omitted.

A few hundred Watt at a minimum would be my first guess.

Yeah that is what is used for moonbounce today (if not full legal power - 1500W for US amateurs) but these little panels won't put out anything remotely close to that. Hence my skepticism.

Y'all can run at 1500W? Here in Germany the legal limit (depending on band of course) is 750W.
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