Home |
Search |
Today's Posts |
#1
![]() |
|||
|
|||
![]()
Frankly speaking no standing waves. Waves always travel. In air travel the
pressure pulse. When the two waves travel in opposite directions they interfere. See: http://en.wikipedia.org/wiki/Kundt's_tube "The sound generator is turned on and the piston is adjusted until the sound from the tube suddenly gets much louder. This indicates that the tube is at resonance, which means its length is a multiple of the wavelength of the sound wave. At this point the sound waves in the tube are in the form of standing waves, and the amplitude of vibrations of air are zero at equally spaced intervals along the tube, called the nodes." Between the nodes are places where the amplitude is doubled. So the places with doubled amplitude are standing. Pressure pulse travel. In antennas is electron gas. The first place where the doubled amplitude (amplitude means voltage or electron density) appear is end of the radials. The next is halve wave apart from the end. Such places radiate strong electric waves. They are the source of radiation. Of course the next source is weaker because some part of energy is radiated. But such is stronger than the trawled source (normal voltage pulse) If antenna has only one source it is omnidirectional. If two or more is directional because the waves from different sources interfere. The halve wave dipole has the two sources. The next two appear than a dipole is longer than the wave length. So that what R. Clark wrote is obvious: "[* What is this proportional and proportionate mean? For a dipole of 0.05 WL to a dipole of 0.5WL, the far field change for that 10:1 variation is negligible. However, for a dipole of 0.5WL to a dipole of 1.25WL, the far field change for that 2.5:1 (a smaller proportion) variation is very noticeable.] The above is the antenna with the Helmholtz' pressure wave. Could anybody describe the antenna with the Heavisde's TEM waves? In a few words. Do not send mi to library. S* |
#2
![]() |
|||
|
|||
![]()
On Thu, 17 Sep 2009 19:15:56 +0200, Szczepan Bia?ek
wrote: If antenna has only one source it is omnidirectional. If two or more is directional because the waves from different sources interfere. The halve wave dipole has the two sources. The next two appear than a dipole is longer than the wave length. So that what R. Clark wrote is obvious: "[* What is this proportional and proportionate mean? For a dipole of 0.05 WL to a dipole of 0.5WL, the far field change for that 10:1 variation is negligible. However, for a dipole of 0.5WL to a dipole of 1.25WL, the far field change for that 2.5:1 (a smaller proportion) variation is very noticeable.] In the space of two sentences you contradict yourself. You don't get it, do you? 73's Richard Clark, KB7QHC |
#3
![]() |
|||
|
|||
![]()
On Sep 17, 10:15*am, Szczepan Białek wrote:
Frankly speaking no standing waves. Waves always travel. In air travel the pressure pulse. When the two waves travel in opposite directions they interfere. See:http://en.wikipedia.org/wiki/Kundt's_tube "The sound generator is turned on and the piston is adjusted until the sound from the tube suddenly gets much louder. This indicates that the tube is at resonance, which means its length is a multiple of the wavelength of the sound wave. At this point the sound waves in the tube are in the form of standing waves, and the amplitude of vibrations of air are zero at equally spaced intervals along the tube, called the nodes." Between the nodes are places where the amplitude is doubled. So the places with doubled amplitude are standing. Pressure pulse travel. In antennas is electron gas. The first place where the doubled amplitude (amplitude means voltage or electron density) appear is end of the radials. The next is halve wave apart from the end. Such places radiate strong electric waves. They are the source of radiation. The problem I immediately see here is that you're probably interested in electromagnetic radiation, not just the electric field. The result, as I see it, is that the rest of your discussion is based on a completely false premise. But see below. .... The above is the antenna with the Helmholtz' pressure wave. Could anybody describe the antenna with the Heavisde's TEM waves? In a few words. Do not send mi to library. S* Others have tried to describe radiation from linear antennas in reasonably simple terms. One of the best I know is Joseph Boyer's pair of articles from May and June, I think it was, 1978 "Ham Radio" magazine: "The Antenna-Transmission Line Analog." It's a non- mathematical work; it will leave you with answers with not a lot to back them up, but they do match what we observe, as far as I understand it. I have these as a PDF, along with a fairly important section from a book referenced by the articles. Cheers, Tom |
#4
![]() |
|||
|
|||
![]()
On Sep 17, 12:15*pm, Szczepan Białek wrote:
If antenna has only one source it is omnidirectional. If two or more is directional because the waves from different sources interfere. More study is needed on your part, S*. Consult the textbooks of the authors that already have been listed, and quoted here. Your unproven, personal opinions are not sufficient to support some of the statements you post-- which accounts for the "negative" comments responding to them. Every single real-world antenna in existence has more than one source along its length that contributes to its radiation pattern, and therefore has some directionality. Your study and accurate understanding of the works of the authors mentioned will prove this. RF |
#5
![]() |
|||
|
|||
![]() "Richard Clark" wrote ... On Thu, 17 Sep 2009 19:15:56 +0200, Szczepan Bia?ek wrote: If antenna has only one source it is omnidirectional. If two or more is directional because the waves from different sources interfere. The halve wave dipole has the two sources. The next two appear than a dipole is longer than the wave length. So that what R. Clark wrote is obvious: "[* What is this proportional and proportionate mean? For a dipole of 0.05 WL to a dipole of 0.5WL, the far field change for that 10:1 variation is negligible. However, for a dipole of 0.5WL to a dipole of 1.25WL, the far field change for that 2.5:1 (a smaller proportion) variation is very noticeable.] In the space of two sentences you contradict yourself. You don't get it, do you? "If antenna has only one source" means the monopole antena (the second source is "graved") "The halve wave dipole has the two sources" means "dipole has visible the both ends". O.K now? S* |
#6
![]() |
|||
|
|||
![]() "Richard Fry" ... On Sep 17, 12:15 pm, Szczepan Białek wrote: If antenna has only one source it is omnidirectional. If two or more is directional because the waves from different sources interfere. More study is needed on your part, S*. Consult the textbooks of the authors that already have been listed, and quoted here. Your unproven, personal opinions are not sufficient to support some of the statements you post-- which accounts for the "negative" comments responding to them. I wrote: "Do not send me to librery". Every single real-world antenna in existence has more than one source along its length that contributes to its radiation pattern, and therefore has some directionality. I wrote" "Pressure pulse travel" I means that in monopole antena is one strong source on the and and traveling source "along its length" . Your study and accurate understanding of the works of the authors mentioned will prove this. Tell me who is right: Helmholtz or Heaviside? S* |
#7
![]() |
|||
|
|||
![]()
On Sep 18, 2:08*am, Szczepan Białek wrote:
I wrote" "Pressure pulse travel" I means that in monopole antena is one strong source on the and and traveling source "along its length" . I assume from what you posted before that you meant to write "in a monopole antenna there is one strong source on the END..." Could you please post the reason(s) you think so? Note that only the change in current and charge, over time, produces EM radiation. At the top of a monopole, and at the ends of a dipole the net current is almost zero -- so those locations generate very little of the total EM radiation from these antennas. RF |
#8
![]() |
|||
|
|||
![]()
Szczepan Białek wrote:
"The halve wave dipole has the two sources" means "dipole has visible the both ends". A 1/2WL dipole is a standing wave antenna. Are you saying that the forward energy is one source and the energy reflected from the ends is a second source? -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#9
![]() |
|||
|
|||
![]()
K7ITM wrote:
"The Antenna-Transmission Line Analog." It's a good analog. For instance a 1/4WL open-wire open-circuit stub made with resistance wire with a resistivity of 0.0000021 ohms-m has a feedpoint impedance of 35 ohms according to EZNEC. The current distribution is a close approximation to a 1/4WL monopole. The additional resistance over copper approximates the energy lost to radiation in a 1/4WL monopole. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#10
![]() |
|||
|
|||
![]()
Richard Fry wrote:
At the top of a monopole, and at the ends of a dipole the net current is almost zero -- so those locations generate very little of the total EM radiation from these antennas. Since the forward current and reflected current are equal in magnitude and opposite in phase at the ends, they act like transmission line currents and the magnetic fields cancel at the ends. They are in phase at the feedpoint - hence the maximum radiation at that point. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Poynting Vector in Standing Waves | Antenna | |||
Standing morphing to travelling waves, and other stupid notions | Antenna | |||
Standing Waves (and Impedance) | Antenna | |||
Traveling Waves, Power Waves,..., Any Waves,... | Antenna | |||
Imaginary Standing Waves? | Antenna |