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Solar Radiation AM

  1. Jun 10, 2008 #1
    First of all, this is my first post here. So, hello everyone! :smile:

    I have a question about the solar radiation and that I don't seem to be able to find an answer for on the net.

    I'm building an IR transceiver for data transmission that should be able to withstand some amount of direct sunlight on the photodiode. I already made some prototypes, and filtering out the DC current generated by direct sunlight it's an easy task. But now I'm particularly worried if the solar radiation in space (with no atmosphere filtering) may have some "amplitude modulation" around the megahertz range (let's say, from 10 kHz to 10 MHz in both visible and IR spectrums) that could get thru the DC block.

    Every study I could find on the net is about longer term variations of the solar radiation (from hours to centuries) and I can't find anything on shorter term ones. Maybe it's just because there is no variation on shorter terms... But, you know... :wink:

    Anyway, if anyone here could shed some light on the subject, I would be grateful.

  2. jcsd
  3. Jun 10, 2008 #2
    Sun radiates in radio range

    I'm in solar astronomy but not an expert in radio. The sun radiates in the range you
    are in interested in from the 'quiet sun' and from 'active regions'. there are variations as
    these regions evolve and the sun rotates. Also, eruptions such as flares and coronal mass ejections cause increases in radio emission over timescales of minutes to hours. I believe there are websites showing plots of emission versus time measured by satellites. Also, there are several ground based radio observatories that provide such data. google:
    solar radio observatory, or: in-situ solar radio emission
  4. Jun 11, 2008 #3
    Yeah. I know the sun radiates in the radio range. But I'm not interested in electromagnetic radiation in the megahertz range. I'm interested in "amplitude modulation" of the light emitted by the sun in the megahertz range. I mean, quick variations in the IR (or visible) light intensity that would get past the DC current block I used on the photodiode.

  5. Jun 11, 2008 #4
    AM should be quite small

    sorry, i didnt read that carefully enough. there is not a lot published on this topic, probably because the modulations in IR intensity in the megahertz range are very small. I would guess the relative amplitude is less than 1/1,000,000. the flucutations caused by passage through earth's atmosphere are much larger.
    Last edited: Jun 11, 2008
  6. Jun 11, 2008 #5


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    I would worry more about atmospheric effects. The timescale for atmopsheric seeing (star twinkling) is upto a few 100Hz.
  7. Jun 15, 2008 #6
    Sorry for the late reply, but I've been quite busy.

    Exactly what I guessed at first. Just wanted someone else's opinion too.

    Interesting. I will dig into that. However, luckily for us, atmosphere is nothing to be concerned about. :smile:

    Thanks everyone.
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