Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How efficient radiosignals are

  1. Oct 26, 2003 #1
    Hey there

    I've been wondering just how efficient radiosignals are... If I were to place a transmitter broadcasting 1 Watt then what would I be recieving at say 10 meters away? Of course the antennas and frequencies are adjusted to near optimal with regards to dimensions, size and frequency in both reception and transmition, so I need a best case guess... Any radioamateurs or other wise people around? :-D

    Best regards

    Thomas Hansen
     
    Last edited by a moderator: Feb 6, 2013
  2. jcsd
  3. Oct 26, 2003 #2

    russ_watters

    User Avatar

    Staff: Mentor

    Not much gets absorbed by the atmosphere, but the problem is keeping the signal coherent. It is possible to keep some radio signals highly coherent by shaping the transmitter in a parabola.
     
  4. Oct 27, 2003 #3
    With my limited knowledge on radiowaves and radiosignals I can only help a little bit: I know that it is important that the antenna is 1/4 of the wavelength of the signal you're sending/ recieving because you will then have the optimal dimensions of the antennas and therefore have the most powerful signal reception. My question is, just how much of a 1 Watt signal will you recieve 10 metres away, if all of the equipment is properly adjusted? ( thats around 30 feet IIRC)
    I need it to be with ordinary antennas, Parabolic is not and option.
    The question is so simple, and the answer straightforward, it is probably even posible to calculate it... I just don't know how! :-(
    Hope this narrows it down a little bit.

    Best regards

    Thomas Hansen
     
  5. Feb 13, 2004 #4
    Some HAM operators sent a radio signal from the US to New Zealand,
    Try 1/D^2
    the inverse square law; for all your needs (if it fits of-cource)
    Nice Coder
     
  6. Feb 14, 2004 #5

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    Indeed, but if he's using an "ordinary antenna" (dipole?) orented say north-south, there won't be much signal going in the north-south direction.
     
  7. Feb 14, 2004 #6
    "Indeed, but if he's using an "ordinary antenna" (dipole?) orented say north-south, there won't be much signal going in the north-south direction." ??
    you may mean that if he is using a vertically polerised dipole, that if the transmitting antenna was horizontally polerised that he wouldn't get much signal?
    The minimum signal comming fro mthe transmitting antenna (at 90 degrees) is only -3DB, so its not that much (how many op-amps only have a 3db gain?)
    :smile:
    De Nice Codre
     
  8. Feb 15, 2004 #7

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    I was thinking of a horizontal fullwave dipole. But the point was that his question depends on what "ordinary antennas" means.
     
  9. Feb 17, 2004 #8
    on long wavelengths horizontal dipoles are predominantly used, for short wavelengths yagi's, and vertically polerised dipoles are used.

    It does not matter what his definition of an 'ordinary antenna' is, as long as they are using the same antenna, with the same polerisation and are not using directional antenna's pointing away from each other!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?