Comments for VA2LTF - Les Télécommunications Foulab » English http://va2ltf.foulab.org Foulab radiotechnical blog Thu, 17 May 2012 10:58:35 +0000 hourly 1 http://wordpress.org/?v=3.3.2 Comment on Electromagnetic Spectrum Chart by VA2WHY http://va2ltf.foulab.org/2012/04/electromagnetic-spectrum-chart-2/#comment-66 VA2WHY Thu, 17 May 2012 10:58:35 +0000 http://va2ltf.foulab.org/?p=408#comment-66 That's interesting. I'm curious - did the radio astronomers document this information formally somewhere, or has it ended up being kind of an oral tradition, passed along in class notes and code. These quasi-documented things evolve in funny ways. For example in a lot of places, i found people had inserted cyan as a band in the visible spectrum. NASA, however, had not yet done so :-). That’s interesting. I’m curious – did the radio astronomers document this information formally somewhere, or has it ended up being kind of an oral tradition, passed along in class notes and code. These quasi-documented things evolve in funny ways. For example in a lot of places, i found people had inserted cyan as a band in the visible spectrum. NASA, however, had not yet done so :-).

]]> Comment on Electromagnetic Spectrum Chart by Anne http://va2ltf.foulab.org/2012/04/electromagnetic-spectrum-chart-2/#comment-65 Anne Tue, 15 May 2012 17:06:58 +0000 http://va2ltf.foulab.org/?p=408#comment-65 It's worse than that for visible light. At the IR end, the eye's sensitivity falls off, but you can still see a bright enough light. I remember reading about a guy who'd jury-rigged some IR filter glasses that were apparently opaque, but in bright sunlight there was enough IR that you could still see. At the UV end, I suspect the situation's even messier, because there's overlap between the frequencies you can see and those that damage your eyes. For the microwaves, radio astronomers have their own names for the various bands, and sometimes letter designations that may or may not agree with the radar names. For example, L-band is about 1100 MHz to about 1800 MHz, S band is about 2 GHz to 3 GHz, and C band is about 3 GHz to 4 GHz. You see these in the Arecibo control software (natural enough because they also have a radar transmitter there) but also on the Green Bank telescope and the VLA. Used to be the VLA was more heavily into the band letters, but I suspect that with the new EVLA correlators they're moving, along with the rest of radio astronomy, to just using frequencies. Not least because we're using fractional bandwidths as high as a half or so. It’s worse than that for visible light. At the IR end, the eye’s sensitivity falls off, but you can still see a bright enough light. I remember reading about a guy who’d jury-rigged some IR filter glasses that were apparently opaque, but in bright sunlight there was enough IR that you could still see. At the UV end, I suspect the situation’s even messier, because there’s overlap between the frequencies you can see and those that damage your eyes.

For the microwaves, radio astronomers have their own names for the various bands, and sometimes letter designations that may or may not agree with the radar names. For example, L-band is about 1100 MHz to about 1800 MHz, S band is about 2 GHz to 3 GHz, and C band is about 3 GHz to 4 GHz. You see these in the Arecibo control software (natural enough because they also have a radar transmitter there) but also on the Green Bank telescope and the VLA. Used to be the VLA was more heavily into the band letters, but I suspect that with the new EVLA correlators they’re moving, along with the rest of radio astronomy, to just using frequencies. Not least because we’re using fractional bandwidths as high as a half or so.

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