yes you are right on that, the behavior of the energy with distance depends on the source.
Vicente RodrÃguez, Ph.D., E.I.T. RF/Electromagnetics Engineer ETS-Lindgren (an ESCO Company) P.O.Box 80589, Austin TX 78708-0589 phone 512.835.4684 x648 fax 512.835.4729 [email protected] http://www.emctest.com http://home.austintx.com/~vicenter > -----Original Message----- > From: [email protected] [SMTP:[email protected]] > Sent: Thursday, November 30, 2000 4:11 PM > To: [email protected] > Cc: [email protected]; [email protected] > Subject: RE: How does RF travel through outer space? > > > Geez, this question makes me feel like I'm on "Who want to be a > millionaire"! > Brain should have provided multiple choices for his two questions. > > George, good anaolgy re the pumpkin. Here is some other stuff I remember > from my hated electric field classes some 40 years ago. If the radiator > is a > point > source in space, and the energy is equally distributed in a spherical > pattern, > the > energy at any point in space drops off as the cube of the distance from > the > source. > If the radiator is an infinite line, the energy drops off as the square of > the > distance > from the source. If the source is an infinite plane, the energy remains > the > same > regardless of the distance from the plane. Are these right? > > Now to the tough part about RF travelling in space. Note that all energy > we > receive from the sun comes in some form of electromagnetic energy, ranging > from frequncies which give us light, to infrared which gives us heat, in > addition > to all kinds of non-structered RF signals. > > Doesn't electromagnetic energy depend on the sequential exitation of > electrons > from one adjacent molecule to another to "travel" anywhere? It is my > understanding > that space is not a vacuum, but merely a lower pressure than that here on > earth. > The > molecules may be further apart (less dense), but are still out there. The > only > TRUE > vacuum I know of is what they call a "black hole" in space, which > literally > sucks all > nearby matter into it......but this is still a theory. > > Brain, the RF energy, or any other part of the EM spectrum, travels > through > space > just as in the water you mentioned, only with different molecules, and > spacing > of > same. > > These are my FINAL answers. Did I win anything, or must I go home a > loser? > > George > > > > > george_tang%[email protected] on 11/30/2000 03:56:59 PM > > Please respond to george_tang%[email protected] > > To: brian_kunde%[email protected], > emc-pstc%[email protected] > cc: (bcc: George Alspaugh/Lex/Lexmark) > Subject: RE: How does RF travel through outer space? > > > > > We all just carved pumpkins not too long ago. We can use pumpkins to > explain one of these questions. If you put a 5 watt light bulb at the > center of your carved pumpkin, then each square inch of the internal > pumpkin > surface gets the amount of light energy given by the expression: > > 5W / (internal surface area of pumpkin) = light energy per square inch > > Now you move your light bulb to a bigger pumpkin and do the same > calculation. You find that each square inch of your bigger pumpkin gets > less light energy due to a bigger surface area. This is why RF signals > drop > off at the rate of 1/distance squared, since the pumpkin surface area is > proportional to the square of the radius. Light is simply a higher > frequency emission than RF, but the same concept applies. > > As far as "How RF travel through vacuum," you can think of it this way: > RF > is composed of electric field and magnetic field. Electric field is > simply > the attraction force between the positive charges and the negative > charges. > And magnetic field is the interaction between 2 current loops. It is not > hard to imagine that refrigerator magnets will work in vacuum or protons > and > electrons will attract in outer space. RF is simply the electric and > magnetic fields changing polarity at a very rapid rate. > > George > > > > -----Original Message----- > From: brian_kunde [mailto:[email protected]] > Sent: Thursday, November 30, 2000 12:51 PM > To: emc-pstc > Subject: How does RF travel through outer space? > > > > > > Hello, > > I'm sorry if this is too simple of question... "How does RF travel through > outer > space?". > > I will be teaching a class in which this question will come up. I want to > be > prepared with all the basic science behind this principal. I need an > explaination that is simple and easy to understand. > > People seem to have no problem understanding how waves can travel through > mass > such as a body of water but can not understand how it can travel where > there > is > no mass. I also understand that there is a lot of debate over how Light > travels > through space (photons and all). > > Also, I understand that RF signals degrade at a rate of > 1/distance(squared). > What force is causing this attenuation? > > Try to keep it simple for my audience it not all that technical. > Appreciate > the > help. Please forgive any improper punctuation or word misuse. > Brian > > > > > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > > > > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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