8 ms·

The aircraft detection phenomenon isn't far-fetched sci-fi; here's a video showing what it looks like: https://www.youtube.com/watch?v=1gc0vVk3XBg https://www.

The aircraft detection phenomenon isn't far-fetched sci-fi; here's a video showing what it looks like: https://www.youtube.com/watch?v=1gc0vVk3XBg https://www.youtube.com/watch?v=1gc0vVk3XBg Remember that we're talking about a gigantic hunk of airborne metal, with a mandatory 50 miles of separation from any other gigantic hunk of airborne metal. With that said, the article is claiming to do this detection without the waterfall plot or I/Q data, using nothing but a single scalar data point (receiver SNR) recorded once every two minutes. That is far-fetched sci-fi. If the WSPR stations were archiving the raw I/Q data at the SDR input, I might believe something useful could be recovered from that.

ellenhp 5y ago
I mean, sure, measuring occlusion like this is possible in VHF, UHF and beyond. And radar is a real thing that exists, and you can even do passive radar, but to my knowledge you cannot do any of this outside the line of sight of the transmitter and receiver with an object that's only 1-4 wavelengths long. I'd love to be proven wrong because that would be wild and the kind of thing that makes me fall in love with radio all over again, but this source is completely bogus.
- bmurray7jhu 5y ago
  Over-the-horizon radar uses HF to detect distant objects. See https://en.wikipedia.org/wiki/Over-the-horizon_radar https://en.wikipedia.org/wiki/Over-the-horizon_radar
  - ellenhp 5y ago
    With a big antenna array for beamforming, sure, you can do that. You absolutely cannot do over the horizon radar on 10 watts with two omnidirectional antennas though.
    - jrockway 5y ago
      Wait, who is doing WSPR at 10 watts? Most people are just using an unamplified IO pin off their Raspberry Pi or something; milliwatt at best. (It makes WSPR itself all the more impressive, however!)
      - ellenhp 5y ago
        If you have an SSB radio that you can hook up to a PC's sound card using VOX to activate the transmitter, you can use WSJT-X or similar software to do lots of digital modes like WSPR, PSK31, FT-8 and whatever's hot these days. I think best practice for WSPR is to keep power low though, so don't go crazy :)
      - wglb 5y ago
        While there are a lot of folks using very low power on WSPR, there are also a lot on HF doing so with 100 watts, and even more in some cases.
  - 8bitsrule 5y ago
    The 'Russian woodpecker' and the US' OTH-B systems built decades ago used pulsed signals of 1 Million watts and up, with gigantic antenna arrays. [0] Comparison to WSPR is impossible (esp. given the complete lack of non hand-wavey details in the article). If the method were at all feasible, it'd very likely be commercially available). [0] https://fas.org/nuke/guide/usa/airdef/an-fps-118.htm https://fas.org/nuke/guide/usa/airdef/an-fps-118.htm
Reason077 5y ago
> ”mandatory 50 miles of separation from any other gigantic hunk of airborne metal.” There is certainly no 50 miles of mandatory separation between aircraft! Horizontal radar separation is 10 nautical miles at most (much less in busy airspace near airports), and vertical separation is 1000 feet. Of course, the Southern Indian Ocean is very remote and it’s entirely possible that there were no other aircraft within 50 miles of the MH370 flight path.
- KirillPanov 5y ago
  > There is certainly no 50 miles of mandatory separation between aircraft! Over the open ocean, where the MH370 was, there absolutely is: https://en.wikipedia.org/wiki/Separation_(aeronautics)#Longitudinal_separation https://en.wikipedia.org/wiki/Separation_(aeronautics)#Longi... > The golden rule is the 10-minute rule: no two aircraft following the same > route must come within 15 minutes flying time of each other. In areas with > good navaid cover this reduces to 10 minutes At the MH370's cruising speed of 636mph a 10-minute separation is 106 miles! The Boeing 777's cruising speed is way at the high end for commercial airliners. Regardless anything flying over the open ocean between continents will almost certainly be going at least half that speed.
  - denebola 5y ago
    That is only if they are at the same altitude. You seem to have missed the first sentance on that link "If any two aircraft are separated by less than the vertical separation minimum, then some form of horizontal separation must exist. "
  - carl_dr 5y ago
    That might be the golden rule, but it definitely isn't "the rule". If you look on Flightradar24, over the Atlantic for example, you'll see several cases where there are multiple planes well within 15 minutes flying time of each other, on the same track, with separation of 2-3 thousand feet vertically. One example as I write has AA9820 and UA46 following each other at 40,000ft and 37,000ft, at 15nm horizontal separation, and QR740 at 36,000ft about 30nm behind them. When airline traffic is at 100%, you'll routinely see them much closer than that.

ellenhp 5y ago

I mean, sure, measuring occlusion like this is possible in VHF, UHF and beyond. And radar is a real thing that exists, and you can even do passive radar, but to my knowledge you cannot do any of this outside the line of sight of the transmitter and receiver with an object that's only 1-4 wavelengths long. I'd love to be proven wrong because that would be wild and the kind of thing that makes me fall in love with radio all over again, but this source is completely bogus.

bmurray7jhu 5y ago
Over-the-horizon radar uses HF to detect distant objects. See https://en.wikipedia.org/wiki/Over-the-horizon_radar https://en.wikipedia.org/wiki/Over-the-horizon_radar
- ellenhp 5y ago
  With a big antenna array for beamforming, sure, you can do that. You absolutely cannot do over the horizon radar on 10 watts with two omnidirectional antennas though.
  - jrockway 5y ago
    Wait, who is doing WSPR at 10 watts? Most people are just using an unamplified IO pin off their Raspberry Pi or something; milliwatt at best. (It makes WSPR itself all the more impressive, however!)
    - ellenhp 5y ago
      If you have an SSB radio that you can hook up to a PC's sound card using VOX to activate the transmitter, you can use WSJT-X or similar software to do lots of digital modes like WSPR, PSK31, FT-8 and whatever's hot these days. I think best practice for WSPR is to keep power low though, so don't go crazy :)
    - wglb 5y ago
      While there are a lot of folks using very low power on WSPR, there are also a lot on HF doing so with 100 watts, and even more in some cases.
- 8bitsrule 5y ago
  The 'Russian woodpecker' and the US' OTH-B systems built decades ago used pulsed signals of 1 Million watts and up, with gigantic antenna arrays. [0] Comparison to WSPR is impossible (esp. given the complete lack of non hand-wavey details in the article). If the method were at all feasible, it'd very likely be commercially available). [0] https://fas.org/nuke/guide/usa/airdef/an-fps-118.htm https://fas.org/nuke/guide/usa/airdef/an-fps-118.htm

Reason077 5y ago

> ”mandatory 50 miles of separation from any other gigantic hunk of airborne metal.” There is certainly no 50 miles of mandatory separation between aircraft! Horizontal radar separation is 10 nautical miles at most (much less in busy airspace near airports), and vertical separation is 1000 feet. Of course, the Southern Indian Ocean is very remote and it’s entirely possible that there were no other aircraft within 50 miles of the MH370 flight path.

KirillPanov 5y ago
> There is certainly no 50 miles of mandatory separation between aircraft! Over the open ocean, where the MH370 was, there absolutely is: https://en.wikipedia.org/wiki/Separation_(aeronautics)#Longitudinal_separation https://en.wikipedia.org/wiki/Separation_(aeronautics)#Longi... > The golden rule is the 10-minute rule: no two aircraft following the same > route must come within 15 minutes flying time of each other. In areas with > good navaid cover this reduces to 10 minutes At the MH370's cruising speed of 636mph a 10-minute separation is 106 miles! The Boeing 777's cruising speed is way at the high end for commercial airliners. Regardless anything flying over the open ocean between continents will almost certainly be going at least half that speed.
- denebola 5y ago
  That is only if they are at the same altitude. You seem to have missed the first sentance on that link "If any two aircraft are separated by less than the vertical separation minimum, then some form of horizontal separation must exist. "
- carl_dr 5y ago
  That might be the golden rule, but it definitely isn't "the rule". If you look on Flightradar24, over the Atlantic for example, you'll see several cases where there are multiple planes well within 15 minutes flying time of each other, on the same track, with separation of 2-3 thousand feet vertically. One example as I write has AA9820 and UA46 following each other at 40,000ft and 37,000ft, at 15nm horizontal separation, and QR740 at 36,000ft about 30nm behind them. When airline traffic is at 100%, you'll routinely see them much closer than that.