Wow, people do read my posts. I should be more careful about what I write.
Gary Turner wrote: [snip] > While it is true that the EMF, or voltage is inversely proportional to > the distance, the power is reduced by the square of the distance. > (P=e^2/r, P=i^2*r, or P=e*i) Thus a signal with a power density of 1 > Watt per sq meter at 10 meters distance, will have a power density of > .01 Watts per sq meter at 100 meter's distance (in a lossless system). Thankyou for that clarification. [snip] > Which brings us to power density at the receiving end--there ain't much. > Given that the W/sq meter is minuscule, an antenna such as the one the > seti project uses has an effective aperture on the order of 10's of > thousands of sq meters. And that helps. The small beam angle acts to > remove all signals not in the desired direction, so the noise level is > reduced. VLNAs bring sensitivity to a level that a signal energy level > only a few degrees above abs 0 is detectable. Levels a few degrees above abs 0 may be detectable, but that does not imply intelligable. There are some very strong radiating bodies out there; what fraction of a degree of the sky can you pick out with your antenna? A source does not need to be close (in a distance sense) to another source for them to appear close (in a directional sense) from earth. Anthony Campbell <[EMAIL PROTECTED]> worte: [snip] > > I can think of a number of better ways of spending the money/time/spare > > CPU cycles. > > For example? Money: * Feeding people * Make sustainable industry economically viable * Devise an atmosphere cleaner * Land mine clearing programmes * Better and more accessable education Time: * Looking after family * Getting more excercise * Learn another language * Build a boat * Strip a friend's car down * Port octave to be a real win32 app * I have a list of projects here somewhere... Spare CPU cycles: * I dunno, play quake or something. John Hasler <[EMAIL PROTECTED]> wrote: > > ...since no-one has yet devised an antenna which radiates very > > well in all directions... > > That's completely irrelevant. > > > The direction of propagation is perpendicular to the direction of motion > > of the exciting charges (aren't they exciting? ;-) and so the wave > > propagates in the horizontal plane (assuming that your antenna is > > oriented that way. > > The radiation propagates in all directions (though the intensity varies > around the antenna patern). I think you are confounding polarization and > propagation. Is that right? I thought that an ideal dipole would radiate only in a plane. Obviously we don't have ideal dipoles, but that's what I thought the theory said. I am more than happy to take correction here; I have an exam on this stuff in not so many weeks time ;-) Tom
