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Is TV static

  1. Jul 31, 2010 #1
    ...residual signals of CMB radiation from the Big Bang? I've heard and read this before but I'm not too sure how credible this is. Are TV antennas really that strong to pick up CMB?:confused:

    Just wana get this cleared up by an expert. Thanks.
     
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  3. Jul 31, 2010 #2

    nicksauce

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    About 1% of the signal is from the CMB.
     
  4. Aug 1, 2010 #3

    Chalnoth

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    Shouldn't be that surprising, really. About 99% of all of the radiation ever emitted is in the CMB. Just picking up the CMB isn't that hard. The difficult part is picking up the small deviations in temperature from place to place in the sky (which are only about one part in one hundred thousand variations in temperature).
     
  5. Aug 1, 2010 #4

    Chronos

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    The CMB signal is strong enough to be detected by fairly primitive radio antennae, which is how it was first affirmed about half a century ago [re: Penzias and Wilson].
     
  6. Aug 1, 2010 #5

    jimgraber

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    The Planck site says a few percent. It also says the max is at 2 mm, which corresponds to 150 megahertz. (the effect is obviously frequency dependent). So channel 7 has the highest percentage of CMB. Other sources are the sun and lightening and thermal noise from the tv itself. I don't have accurate percentages.
    Best,
    Jim Graber
     
  7. Aug 3, 2010 #6

    collinsmark

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    At the risk of being simplistic, the answer is no. At least not enough to make a worthwhile difference.
    [Edit: well, as others have stated, maybe a couple of percent, maybe. But only a tiny fraction of overall noise.]

    Nearly all of the static you see on TV -- pretty much the entire picture when you tune the TV to an unused station -- is the random thermal noise in the TV's receiver itself. And most of this this noise comes from the a particular component in the TV's receiver called the "low noise amplifier" (LNA). In other words, the the vast majority of the static isn't the "reception" of anything. It's coming from within the TV itself. It's due to the thermal activity of the electrons in the electronics; the LNA playing the biggest role.

    Now you might be asking, "Did you just say that most of the noise comes from something called a 'low noise amplifier'? Isn't that an oxymoron?" Well, yes and no. The term is an engineering term because efforts are made to design the LNA to have as low as noise as reasonably possible (at least an acceptably low amount of noise). Reducing the noise from the LNA increases the "signal to noise ratio" when a signal is present, improving the quality of your viewing experience (and you get the biggest "bang for the buck" by reducing the noise in the LNA as opposed to other components in the receiver).

    But whatever the case, in the end, the amount of CMBR energy within the given bandwidth is well below the thermal noise floor of a typical TV set.
     
    Last edited: Aug 3, 2010
  8. Aug 13, 2010 #7
    What about a radio? How much of that is CMB. Similar proportion (99%) due to radio itself. Just curious. Or would going to the Planck site give me that answer?
     
  9. Aug 13, 2010 #8

    jimgraber

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    would going to the Planck site give me that answer?
    That, plus a little math.
    Do you know the blackbody radiation formula? The CMB has blackbody shape.

    Once again, the answer is frequency(or wavelength) dependent.

    Basically, the farther your frequency is from that of channel 7, ie from the central frequency of the CMB, the less the CMB contributes. It falls off pretty fast. Since radio is much lower frequency than tv the percentage is essentially negligible for the usual radio bands.
    best,
    Jim Graber
     
  10. Aug 13, 2010 #9

    Chalnoth

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    Uh, I'm not so sure about that. Channel 7 is around 175MHz. The central frequency of the CMB is at around 160GHz. All frequencies used for TV/radio are pretty far below the peak of the CMB spectrum.
     
  11. Aug 13, 2010 #10

    jimgraber

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    Oh, well, what's a factor of 1000 between friends?
    In that case it truly is amazing that the CMB is still a few percent of the natural background at TV frequencies.
    best,
    Jim Graber
     
  12. Aug 14, 2010 #11

    Chronos

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    No disagreement about frequency sensitivity. Big disagreement on detectivity over all frequencies. While the CMB peaks at around 160 ghz, it is not noiseless at other frequencies. The sensitivity of the array used by Penzius-Wilson was less good than most modern, hand held, radio receivers with flip antenna. A non-neglible part of that static you hear between channels is courtesy of the CMB.
     
  13. Aug 14, 2010 #12

    Redbelly98

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    Also, the fall-off is slower on the low-frequency side of the peak, approximating a power-law. On the high-frequency end, the fall-off is dominated by the exponential term:

    [tex]I \ = \ \frac{2 h \nu^3 }{ c^2} \cdot \frac{1}{e^{h \nu / k T}-1}[/tex]​
     
  14. Aug 14, 2010 #13

    Chalnoth

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    Indeed. A quick calculation shows that the intensity of the radiation in the 160MHz range would be around 0.3% the intensity at the peak (160GHz). It would drop as [itex]\nu^2[/itex] as you go down from there (i.e. 80Mhz would put you at 1/4th the radiation intensity from the CMB as 160MHz).
     
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