4 ms·

A photo of the dish: https://en.wikipedia.org/wiki/Dwingeloo_Radio_Observatory#/media/File:Radiotelescoop_op_de_Heide_van_het_Dwingelderveld.jpg https://en.wiki

A photo of the dish: https://en.wikipedia.org/wiki/Dwingeloo_Radio_Observatory#/media/File:Radiotelescoop_op_de_Heide_van_het_Dwingelderveld.jpg https://en.wikipedia.org/wiki/Dwingeloo_Radio_Observatory#/m...

kstrauser 2y ago
Lovely! Those big dishes boggle my mind. For example, about Arecibo (https://en.wikipedia.org/wiki/Arecibo_Telescope https://en.wikipedia.org/wiki/Arecibo_Telescope): > The telescope had three radar transmitters, with effective isotropic radiated powers (EIRPs) of 22 TW (continuous) at 2380 MHz Twenty. Two. Terawatts. Now, what that means in context is that if you were looking down the business end of that dish, it would be hitting you with as much RF as though you were standing the same distance away from a 22 TW regular dipole antenna. Put another way, it shines with the same brightness at dead ahead as a 22 TW antenna would show from any direction perpendicular to its length. Because the dish is highly directional, it's only that bright in a tiny angle covering a tiny fraction of the sky. If you're standing behind it, nothing. In front of it? You turn into Dr. Manhattan. It's amazing.
- bobmcnamara 2y ago
  Near field effects have got to be huge on those things.
- slow_typist 2y ago
  A dipole does not radiate isotropically. It has a gain of 2.15 dB over the theoretical isotropic antenna. Gains with respect to the dipole are ERP, not EIRP. But still a lot of power :-)
  - kstrauser 2y ago
    Oops, you're right. That's still really freaking bright!
- 15155 2y ago
  I recommend watching the video series on YouTube re: the ISEE-3 Reboot Project before it's lost to history: https://www.youtube.com/@balint256/search?query=arecibo https://www.youtube.com/@balint256/search?query=arecibo
  - 1oooqooq 2y ago
    https://www.youtube.com/playlist?list=PLPmwwVknVIiUlPbkfBUY1ebP_8hA_4q8j https://www.youtube.com/playlist?list=PLPmwwVknVIiUlPbkfBUY1... link that works on generic ytube clients like newpipe
- viraptor 2y ago
  > If you're standing behind it, nothing Is there actually no back lobe on dishes that size? Or is it just extremely small?
  - sbierwagen 2y ago
    Not zero. Even a full Faraday cage only has 90dB or so of attenuation. But measuring it would be darn hard, since the attenuated signal would be swamped by diffraction, skyscatter and reflection by nearby objects of the stronger side lobes.
- HPsquared 2y ago
  I wonder what the EIRP is of a typical laser pointer (or a high-powered one)

kstrauser 2y ago

Lovely! Those big dishes boggle my mind. For example, about Arecibo (https://en.wikipedia.org/wiki/Arecibo_Telescope https://en.wikipedia.org/wiki/Arecibo_Telescope): > The telescope had three radar transmitters, with effective isotropic radiated powers (EIRPs) of 22 TW (continuous) at 2380 MHz Twenty. Two. Terawatts. Now, what that means in context is that if you were looking down the business end of that dish, it would be hitting you with as much RF as though you were standing the same distance away from a 22 TW regular dipole antenna. Put another way, it shines with the same brightness at dead ahead as a 22 TW antenna would show from any direction perpendicular to its length. Because the dish is highly directional, it's only that bright in a tiny angle covering a tiny fraction of the sky. If you're standing behind it, nothing. In front of it? You turn into Dr. Manhattan. It's amazing.

bobmcnamara 2y ago
Near field effects have got to be huge on those things.
slow_typist 2y ago
A dipole does not radiate isotropically. It has a gain of 2.15 dB over the theoretical isotropic antenna. Gains with respect to the dipole are ERP, not EIRP. But still a lot of power :-)
- kstrauser 2y ago
  Oops, you're right. That's still really freaking bright!
15155 2y ago
I recommend watching the video series on YouTube re: the ISEE-3 Reboot Project before it's lost to history: https://www.youtube.com/@balint256/search?query=arecibo https://www.youtube.com/@balint256/search?query=arecibo
- 1oooqooq 2y ago
  https://www.youtube.com/playlist?list=PLPmwwVknVIiUlPbkfBUY1ebP_8hA_4q8j https://www.youtube.com/playlist?list=PLPmwwVknVIiUlPbkfBUY1... link that works on generic ytube clients like newpipe
viraptor 2y ago
> If you're standing behind it, nothing Is there actually no back lobe on dishes that size? Or is it just extremely small?
- sbierwagen 2y ago
  Not zero. Even a full Faraday cage only has 90dB or so of attenuation. But measuring it would be darn hard, since the attenuated signal would be swamped by diffraction, skyscatter and reflection by nearby objects of the stronger side lobes.
HPsquared 2y ago
I wonder what the EIRP is of a typical laser pointer (or a high-powered one)