5 ms·

An excellent next step would be to use a distributed mesh of these and do interferometry to resolve spatial details on the sky. Observations could be distribut

An excellent next step would be to use a distributed mesh of these and do interferometry to resolve spatial details on the sky. Observations could be distributed with bittorrent and coordinated over a blockchain. There exists off the shelf open source interferometry packages used by professional astronomers today that can be used for the analysis. Accurate positioning is needed but can often be achieved to within a couple of meters using google maps and a sat image of your back yard. EDIT: Do the downvoters hate interferometry? Oh no, it's just because I used the world blockchain. Chill people this is a thread about a blog post about turning a piece of trash into a fun day of amateur astronomy.

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privong 6y ago
> Accurate positioning is needed Accurate timing is also needed to shift and combine the signals from the various dishes. > often be achieved to within a couple of meters using google maps and a sat image of your back yard. Position accuracy requirements are fractions of the wavelength being observed. So for this 11.2 GHz dish (26.8 mm), the position of the dish needs to be known to much better than 2mm. In practice this can be done by observing a bright source with a well-known sky position and then solving for the antenna positions. Aspects of this are discussed in Memo 503 from the Atacama Large Millimeter Array Memo series. http://legacy.nrao.edu/alma/memos/html-memos/alma503/memo503.pdf http://legacy.nrao.edu/alma/memos/html-memos/alma503/memo503...
- tlb 6y ago
  Yes, super-duper accurate timing. A nanosecond of timing error means your focal point moves by an angle equal to 1 foot divided by the distance between dishes. You can calibrate out static timing errors, like due to different lengths of wire. But if the delay is varying for any reason your focal point will be slewing all over the heavens.
petschge 6y ago
Absolute positioning is not that important as long as the relative positions are constant to within a small fraction of the wavelength, in this case to within a millimeter. Which is feasible if you mount it to the side of a building and there isn't too much wind. The much bigger problem is that you need a very accurate clock. Much better than what you can get from a GPS receiver. And lose the blockchain bullshit.
- toomuchtodo 6y ago
  Are there any crystal or photonic oscillators that are up to the task for this time keeping? Or is RF interferometry bound to something like a chip atomic clock [1] (~$4k in low quantities)? [1] https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-clock_9.html https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-...
  - ajford 6y ago
    It's been almost ten years since I last done any of the back end math for this kind of thing, but you could probably get within the ballpark using COTS rubidium oscillators like those used for cell towers. They often show up on auction sites at affordable prices. Use the pulse output to lock a station clock for your local time needs (like syncing your data recording to wall time) and the sine output to lock your mixing oscillators.
  - scionthefly 6y ago
    I suspect that you can get a start by looking at how cosmic ray studies conducted at different sites are coordinated: https://ieeexplore.ieee.org/document/1351816 https://ieeexplore.ieee.org/document/1351816
    - petschge 6y ago
      Except you need closer to 0.01ns for this use case instead of the 55ns you get out of the GPS receivers. And half your data would have more, possibly much more, deviation than that anyway. If you don't know which half, that will lead to loss of sensitivity and possibly artifacts in the reconstructed signal. Interferometry is actually hard.

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privong 6y ago

> Accurate positioning is needed Accurate timing is also needed to shift and combine the signals from the various dishes. > often be achieved to within a couple of meters using google maps and a sat image of your back yard. Position accuracy requirements are fractions of the wavelength being observed. So for this 11.2 GHz dish (26.8 mm), the position of the dish needs to be known to much better than 2mm. In practice this can be done by observing a bright source with a well-known sky position and then solving for the antenna positions. Aspects of this are discussed in Memo 503 from the Atacama Large Millimeter Array Memo series. http://legacy.nrao.edu/alma/memos/html-memos/alma503/memo503.pdf http://legacy.nrao.edu/alma/memos/html-memos/alma503/memo503...

tlb 6y ago
Yes, super-duper accurate timing. A nanosecond of timing error means your focal point moves by an angle equal to 1 foot divided by the distance between dishes. You can calibrate out static timing errors, like due to different lengths of wire. But if the delay is varying for any reason your focal point will be slewing all over the heavens.

petschge 6y ago

Absolute positioning is not that important as long as the relative positions are constant to within a small fraction of the wavelength, in this case to within a millimeter. Which is feasible if you mount it to the side of a building and there isn't too much wind. The much bigger problem is that you need a very accurate clock. Much better than what you can get from a GPS receiver. And lose the blockchain bullshit.

toomuchtodo 6y ago
Are there any crystal or photonic oscillators that are up to the task for this time keeping? Or is RF interferometry bound to something like a chip atomic clock [1] (~$4k in low quantities)? [1] https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-clock_9.html https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-...
- ajford 6y ago
  It's been almost ten years since I last done any of the back end math for this kind of thing, but you could probably get within the ballpark using COTS rubidium oscillators like those used for cell towers. They often show up on auction sites at affordable prices. Use the pulse output to lock a station clock for your local time needs (like syncing your data recording to wall time) and the sine output to lock your mixing oscillators.
- scionthefly 6y ago
  I suspect that you can get a start by looking at how cosmic ray studies conducted at different sites are coordinated: https://ieeexplore.ieee.org/document/1351816 https://ieeexplore.ieee.org/document/1351816
  - petschge 6y ago
    Except you need closer to 0.01ns for this use case instead of the 55ns you get out of the GPS receivers. And half your data would have more, possibly much more, deviation than that anyway. If you don't know which half, that will lead to loss of sensitivity and possibly artifacts in the reconstructed signal. Interferometry is actually hard.