[HN Gopher] Using the Moon as an Echo [video]
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Using the Moon as an Echo [video]
Author : tws
Score : 84 points
Date : 2024-08-08 06:47 UTC (2 days ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| Terr_ wrote:
| > radio telescope
|
| From the title I thought it might be about using lasers against
| lunar retroreflectors, passive arrangements of precise mirrors
| that (usually) reflect light back to its source.
|
| https://en.wikipedia.org/wiki/List_of_retroreflectors_on_the...
| philiplu wrote:
| I was explaining ham radio to my kids last night (something
| neither teenager had ever heard of), and ran across
| https://en.wikipedia.org/wiki/Earth-Moon-Earth_communication.
| dredmorbius wrote:
| My understanding is that before the development of observation
| satellites in the 1960s, radio echos from the Moon were used to
| detect nuclear explosions (testing or military use) from the far
| side of the Earth. Even if direct observations were not possible
| / were limited, so long as the Moon was observable both over the
| test site and a US-friendly (not necessarily US-based) receiving
| station, such signals could be detected.
|
| _The Arecibo's site origins trace back to the 1950s, when
| Cornell University proposed its construction to the Department of
| Defense's Advanced Research Projects Agency (ARPA), which is
| today known as the Defense Advanced Research Projects Agency
| (DARPA). A desire to better understand the composition of the
| ionosphere and how it might impact objects passing through,
| including ballistic missile reentry vehicles carrying nuclear
| warheads, was a key reason for its construction. At the time,
| ARPA was in charge of a broad ballistic missile defense program
| known as Project Defender. It was believed that nuclear warheads
| would produce a distinct signature when reentering the
| atmosphere, making it possible to distinguish them from decoys,
| so long as that signature could be quickly identified and
| categorized. The plan was to use the Arecibo Telescope to help
| gather general, but still valuable information about the
| ionosphere in support of this effort._
|
| <https://www.twz.com/37898/collapsed-arecibo-radio-telescope-...>
| xxdiamondxx wrote:
| Oh hey I have that same ham radio! Kenwood TS-2000. I guess I
| just need a giant radio telescope...
| _whiteCaps_ wrote:
| A cross polarized Yagi can do EME bounce as well. You need an
| az/el rotator to track the moon though.
| nullc wrote:
| You can skip the elevation if you don't mind being limited to
| working when the moon is near the horizon. You don't need to
| deal with polarization if the far side can handle it.
| motohagiography wrote:
| What a useful tool that saves me time. My weekend project this
| week was literally just writing a canon for modular synth that
| used a moon bounce for the second voice. I figured I could
| compose it with a delay set to 2.7sec, and then play with the
| clock via Maths for a performance- but their plugin sounds like
| this is more complex and interesting.
|
| Lunar bounce canons could become an entire form arising from that
| 2.7sec constraint.
| firesteelrain wrote:
| This is really cool. A small niche of ham radio operators perform
| EME (Earth Moon Earth) contacts all the time
| ajsnigrutin wrote:
| There are also digital modes that use radio scatter and
| reflections (meteorites, airplanes,....) to communicate "further"
| than line-of-sight allows.
|
| It's a quite well know "ham radio thing", although it's mostly
| "empty", and few hams actually use those modes.
| assimpleaspossi wrote:
| Moon bounce was quite the thing as a ham radio operator in the
| 1960s and 1970s when I got started. I was trying to put together
| my own system for the world's first EME bounce on 220Mhz back
| then but was eventually beat out as life, and my first job out of
| school, got in the way.
| softjobs wrote:
| https://www.audiothing.net/effects/moon-echo/
| meitham wrote:
| This is the main plot from 3 body problem using the moon to
| magnify the signal!
| meta-level wrote:
| it was neither the moon or a main plot in 3 body problem. And
| surely no signals have been magnified by the moon..
| nullc wrote:
| IIRC wasn't it using solar plasma as an astrophysical maser?
|
| https://en.wikipedia.org/wiki/Astrophysical_maser
| meitham wrote:
| To be honest I am beginning to doubt my own understanding of
| the plot, I never read the book but watched the tv show with
| my wife and my recollection was just the moon itself would
| magnify the signal
| nullc wrote:
| ah maybe they made it the moon in the TV show. That
| wouldn't make a lot of sense, but.. TV so who knows.
| nullc wrote:
| I've successfully used moon bounce one way, with my signal from
| California on a simple 8el yagi being heard by a big station in
| Italy. -- using a digital mode, of course, getting phone through
| requires a BIG station on both sides since there is about 250dB
| of path loss.
|
| I haven't managed a two way contact because there is some
| broadband noise on 2m in the same direction that the moon rises
| that raises my noise floor in that direction by more than 10dB.
|
| I've made a fair number of contacts via meteor scatter, however.
| jeffwass wrote:
| That's awesome!
|
| Did you connect with the Italy station before the EME to see if
| they could hear you, or did you just broadcast out into the
| void hoping for a listener somewhere else?
| nullc wrote:
| The latter! Then I got a signal report back online from I3MEK
| (who apparently has a fairly impressive looking quad antenna
| array: https://cdn-bio.qrz.com/k/i3mek/Dscn1593B.jpg ). I've
| also been heard via the EME path from Texas.
|
| If I ever manage to squash my noise problem, I may bother
| trying to schedule some contacts as it's not unusual to do so
| for EME. But right now I don't want to waste people's time
| when I know that I'm deaf.
|
| (It's really obvious that I'm deaf too, because I can just
| rotate the antenna and watch the noise floor drop).
| fullspectrumdev wrote:
| Now you gotta tell us more about the meteor scatter trick :)
| albert_e wrote:
| I am out of my depth here
|
| What they are beaming at the moon are not mechanical sound waves
| (which obviously won't cross the vacuum that separates earth and
| moon) but radio waves (= electro magnetic radiation)
|
| Since we are talking about audio waves at both input and output
| of the demonstration ...there is presumably a conversion of audio
| waves to radio waves -- possibly using some form of modulation
| like AM or FM to encode the audio information.
|
| Assuming it is FM modulated, given that the return signal has all
| kinds of doppler effects due to relative velocities ... we can't
| simply tune into the base frequency of the FM Modulation carrier
| wave ... but need to correct it with each passing minute maybe.
|
| And the frequency modulation encoded on top of the carrier wave
| should also be scaled back proportionally based on doppler
| correction.
|
| Once we do that though...why wouldn't the echo sound identical to
| the origibal?
|
| I didn't quite follow why there is still a change in pitch of the
| audio between input and output.
|
| Did they simply skip the second step of error correction
| described above and are showing the resulting distortion in
| recovered audio after FM demodulation?
| nullc wrote:
| They're using single sideband. Effectively their audio is just
| being shifted up to the moon frequency and back down again.
| (or, alternatively, like AM but with no carrier or secondary
| image)
|
| The amount of doppler depends on what frequency they are at and
| where the moon is. One can set an offset between RX and TX
| frequency, but one doesn't have to.
| lebuffon wrote:
| Moon bounce communication is most perplexing to the flat earth
| society They refuse to "believe" that it is not trickery. LOL
| bxguff wrote:
| Moonbounce! The amateur extra license is tough but its the
| coolest ham enthusiast flex. one day :_)
| euroderf wrote:
| I remember wondering way back when (60s or 70s?) why the heck did
| radio astronomy get so much funding - so much money was poured
| in.
|
| Only later was it revealed that once in a blue moon (heh), things
| were aligned so that the US could use bounces off the moon to
| detect and analyze a certain class of Soviet radars.
|
| Those periods of use for the radio telescopes in question were
| booked well in advance.
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