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Detection of Earth's radio broadcasts at interstellar distances

  1. Mar 10, 2012 #1
    I'm trying to understand the entry labeled 1.2.3 on this page - http://setifaq.org/faq.html#1.2.3

    The main point of confusion, for me, is what they mean by Tsys. At first, I assumed it referred to the temperature of the telescope, but in the table of results, its value changes depending on the frequency being considered and it ranges from millions of kelvin to 40-50 kelvin.

    What does Tsys mean?

  2. jcsd
  3. Mar 11, 2012 #2


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    no you are NOT looking at millions of K thats surface/core of the sun etc temps

    Tsys = is the system temperature (Kelvins)
    All electronics generate heat and this has an undesirable effect on the sensitivity of a receiver. For very sensitive receivers, like used in radio astronomy, the receiver system is encapsulated and cooled with (usually) liquid nitrogen. This has the effect of bring down the temperature of the receiver components and therefore substantially decreasing the noise they produce.... the less noise, the more sensitivity. Temps of less than 20 Kelvin are achieveable.

    If you do a bit of reading, you will discover that in radio astronomy signal level is usually measured in its temperature above the backgrond noise
    there is masses of info on google.

    Last edited: Mar 11, 2012
  4. Mar 11, 2012 #3
    Here is the contents of the table I was referring to:

    (I hope that's readable, it didn't really copy well.)

    In that table, the value for Tsys is varying depending on the frequency being examined, and they are indeed using a temperature of 68 million kelvin for one of them. The reason I started the thread is to see if anyone knows why they would be using such a temperature?

    I'd also be interested in any other comments that people have on this calculation.
    Last edited: Mar 11, 2012
  5. Mar 11, 2012 #4


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    I really dont see why they are mixing Tsys into a transmitter situation
    Tsys is purely a function/feature of the receiver sensitivity as I stated in my previous post.
    In any normal transmitter, system temperature is only a factor of making sure the transmitter is as efficient as
    possible... ie. its not overheating

    I am well versed with Tsys of a receiver, as it is important in a number of activities I undertake both at work
    and in my radio activities at home.

    also awaiting any other comments

    Last edited: Mar 11, 2012
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