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Antenna reception theory
"Cecil Moore" bravely wrote to "All" (30 Nov 05 15:53:50)
--- on the heady topic of " Antenna reception theory" CM From: Cecil Moore CM Xref: core-easynews rec.radio.amateur.antenna:220639 I wonder if it is possible to directly measure an E field by the effect of the virtual quanta in its close vicinity? CM If the effect of virtual quanta could be measured, CM would they still be virtual? Yes, there is a measurable force. The Casimir Effect is the action virtual particles have on a pair of parallel metal plates, pushing them together (only by an extremely tiny amount). This is because more virtual particles are created outside the plates than between them. A*s*i*m*o*v .... There are subliminal messages in Campbell's Alphabet Soup! |
Antenna reception theory
"Jim Kelley" bravely wrote to "All" (30 Nov 05 09:56:52)
--- on the heady topic of " Antenna reception theory" JK From: Jim Kelley JK Xref: core-easynews rec.radio.amateur.antenna:220642 JK Asimov wrote: I think a saturable core can be used to measure a static magnetic field. Early computer magnetic core memories worked like this. JK I was referring to the similarity to a rotating coil gaussmeter. I JK think what you're describing now is something more akin to the JK fluxgate magnetometer. Relativity transforms static fields into dynamic fields by adding a velocity component to the measurement. JK I see. Is Omni magazine still in print by any chance? Omni is not my cup of tea. Much too glossy for me! What I meant was if the person taking the measurement is in motion relative to the field, then the field will seem to be dynamic. A*s*i*m*o*v .... This is an SOS call from the mining ship Red Dwarf |
Antenna reception theory
Roy Lewallen wrote:
"You can find the explanation for why this is in any electromagnetic text." I found it in Terman. As we all know, we place correctly polarized dipoles, for example, parallel to the wavefront for maximum response. Terman confirms the electric field in this instance induces no energy in the antenna. It all comes from the magnetic field. If antenna current flows, no matter where it comes from, loss resistance causes a voltge drop. That`s why the wire needs to be perfect. The electric field produces no voltage in the antenna because the wavefront has the same voltage across its entire surface. That`s because it all left the same point at the same time. So, a wire parallel to the front has no difference of potential induced by the wavefront`s electric field. It all must come from the mgnetic field. On page 2 of his 1955 edition, Terman says: "The strength of the wave measured in terms of microvolts per meter of stress in space is also exactly the same voltage that the MAGNETIC FLUX (my emphasis) of the wave induces in a conductor 1 m long when sweeping across this conductor with the velocity of light." From the above, it is seen that the electric field is not effective in inducing current in a receiving antenna parallel to a wavefront. All the energy intercepted by the antenna is induced by the magnetic field. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
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Antenna reception theory
It looks like time to remind readers that charge isn't the same as
electrons. On a wire, charge moves at nearly the speed of light, while electrons only go a few miles per hour. Most of the relevant theory actually deals with the interaction of fields and charge, not fields and electrons. Roy Lewallen, W7EL |
Antenna reception theory
Roy Lewallen wrote: It looks like time to remind readers that charge isn't the same as electrons. On a wire, charge moves at nearly the speed of light, while electrons only go a few miles per hour. Most of the relevant theory actually deals with the interaction of fields and charge, not fields and electrons. Roy Lewallen, W7EL Good point. Charge can be holes, or electrons, or even ions. It is the fields which move at the speed of light. Charge tends to have to hang around with the charge carriers. But once a field arrives someplace, it will immediately influence the motion of charges that happen to be hanging around there locally. ac6xg |
Antenna reception theory
"Richard Harrison" bravely wrote to "All" (01 Dec 05 14:18:33)
--- on the heady topic of " Antenna reception theory" RH From: (Richard Harrison) RH Xref: core-easynews rec.radio.amateur.antenna:220709 RH Roy Lewallen wrote: RH "You can find the explanation for why this is in any electromagnetic RH text." RH I found it in Terman. [,,,] RH From the above, it is seen that the electric field is not effective in RH inducing current in a receiving antenna parallel to a wavefront. All RH the energy intercepted by the antenna is induced by the magnetic field. That is outright false. Because I can very easily demonstrate detecting a static E-field by waving a sensitive probe across it. An antenna is just a stationary probe with a moving E-field. It is equivalent. Terman sucks. A*s*i*m*o*v .... Horse sense is the result of stable thinking. |
Antenna reception theory
Asimov wrote:
"Terman sucks." Termn`s writings have been exposed for anyone to criticize for most of a century. His 1955 edition has been out there for 50 years. No retractions or corrections are necessary. Detection of static E-fields is not relevant. Charles Coulomb in 1785 showed electric charges exert forces on each other that are inversely proportional to the square of the distance between them. This was the birth of the "inverse square law" as Coulomb`s discovery applies to magnetic attraction and repulsion, too. In an electromagnetic field, propagation depends upon the electric field begetting a magnetic field and vice versa. On average, each field contains 50% of the total energy. The electromagnetic field of an antenna could be calculated from the distribution of voltage on the conductors. Problem is voltmeter leads would be in the r-f field and this would tend to make measured voltages inaccurate. R-F current is conveniently and accurately measured with a thermocouple ammeter. Strength of an electromagnetic wave is usually measured and quoted in terms of its electric field in volts per meter. This is the number of volts which would be induced in a one-meter length of wire placed in the field parallel to the electric lines of force. Volts in the wire are produced by movement of magnetic flux across the wire. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
"Jim Kelley" bravely wrote to "All" (02 Dec 05 11:17:51)
--- on the heady topic of " Antenna reception theory" JK From: Jim Kelley JK Xref: core-easynews rec.radio.amateur.antenna:220745 JK Asimov wrote: "Richard Harrison" bravely wrote to "All" (01 Dec 05 14:18:33) --- on the heady topic of " Antenna reception theory" RH From: (Richard Harrison) RH Xref: core-easynews rec.radio.amateur.antenna:220709 RH Roy Lewallen wrote: RH "You can find the explanation for why this is in any electromagnetic RH text." RH I found it in Terman. [,,,] RH From the above, it is seen that the electric field is not effective in RH inducing current in a receiving antenna parallel to a wavefront. All RH the energy intercepted by the antenna is induced by the magnetic field. That is outright false. Because I can very easily demonstrate detecting a static E-field by waving a sensitive probe across it. An antenna is just a stationary probe with a moving E-field. It is equivalent. JK Consider the direction the E field is moving and which direction any JK electrostatically induced current might flow. Then apply the same JK criteria to a magnetic field. JK A*C*6*X*G JK Terman sucks. I regret having written that Terman sucks. However, I'm reminded that there is a lot of stuff missing in the 1955 edition of Encyclopedia Britanica up in the attic. Clearly I don't say the EB sucks either, so a 1955 book on electromagentic wave theory might be missing a few things as well. Unless you believe everything that there ever is to learn about EM is that 1955 book. But it is wrong to state that the magnetic field alone is responsible for the interception of wave energy in a metallic conductor. A*s*i*m*o*v .... Isaac Asimov : 1920-1992 : Gone to the stars! |
Antenna reception theory
Richard Harrison wrote:
. . . Strength of an electromagnetic wave is usually measured and quoted in terms of its electric field in volts per meter. This is the number of volts which would be induced in a one-meter length of wire placed in the field parallel to the electric lines of force. . . If the wavelength is 1 m, the voltage induced in the center of an open-circuited 1 m diple by a 1 V/m field is 0.5 volt, not 1 volt. Roy Lewallen, W7EL |
Antenna reception theory
Roy,
What is the voltage measured between the bottom-end of a 1 metre vertical antenna and a perfect ground when the field strength is 1 V/m and the wavelength is 1 m. ---- Reg. |
Antenna reception theory
Reg Edwards wrote:
Roy, What is the voltage measured between the bottom-end of a 1 metre vertical antenna and a perfect ground when the field strength is 1 V/m and the wavelength is 1 m. 1 volt. Roy Lewallen, W7EL |
Antenna reception theory
"Roy Lewallen" wrote in message ... Reg Edwards wrote: Roy, What is the voltage measured between the bottom-end of a 1 metre vertical antenna and a perfect ground when the field strength is 1 V/m and the wavelength is 1 m. 1 volt. Roy Lewallen, W7EL ======================================== Thank you Roy. I don't doubt that your answer conforms to the learned text books on the subject. But I am suspicious the text books may be wrong. I will do some calculations related to radiation resistance and power available to a matched receiver. If I think my suspicions are correct then I will come back to you. ---- Reg. |
Antenna reception theory
Reg Edwards wrote:
Thank you Roy. I don't doubt that your answer conforms to the learned text books on the subject. But I am suspicious the text books may be wrong. I will do some calculations related to radiation resistance and power available to a matched receiver. If I think my suspicions are correct then I will come back to you. ---- Reg. To tell the truth, I got the result for a wire over ground from an NEC-2 model, after first checking to make sure I got the theoretical 0.5 volt for the center of a dipole in free space. (NEC-2 has provision for applying a plane wave to the model.) In the process of confirming the 0.5 volt value, I found an error in a popular text, Balanis, _Antenna Theory, Analysis and Design_. On p. 61, he incorrectly states that the current along a short dipole "can be assumed to be constant", which isn't true, and from that concludes that the "induced voltage" would be 1 volt when the dipole feedpoint is short circuited. How he defines "induced voltage" with a shorted feepoint isn't clear, but the uniform current assumption he used to get it is incorrect. Kraus, in _Antennas_, and others get it right, and modeling confirms it. Roy Lewallen, W7EL |
Antenna reception theory
Roy, you have anticipated my thoughts on the subject.
Nevertheless, I will do some calculations. The proof of the pudding lies in the type of computer programs whose input data does not depend on unreliabe human imagination about antenna gain, mirror images and reflections from the ground. I have no access to the learned text books or computer programs. ---- Reg, G4FGQ |
Antenna reception theory
Reg Edwards wrote:
Roy, you have anticipated my thoughts on the subject. Nevertheless, I will do some calculations. You should be able to reason the wire-over-ground case as follows: Imagine a plane wave of 2 V/m intensity striking a 2 m long open circuited dipole in free space. The open circuit voltage should be 4 times as great as it would be for a 1 V/m wave striking a 1 m long dipole. If you bisect the system with a ground plane, you have half the dipole and half the field above ground -- that's a 1 m wire and 1 V/m field. And half the original dipole's voltage appears between the bottom end of the wire and ground. So the resulting voltage is twice what it would be at the center of a 1 m dipole in free space. The proof of the pudding lies in the type of computer programs whose input data does not depend on unreliabe human imagination about antenna gain, mirror images and reflections from the ground. I have no idea what you're talking about there, but I'm sure that whatever it is, it must not apply to the programs you write. I have no access to the learned text books or computer programs. Sure you do, as does anyone with access to this newsgroup. Texts are readily available by web order for the price of a very few bottles of mediocre wine. Some have even been scanned and posted on the web. And NEC-2 is free and can be downloaded from the web. But some people just can't deal with any idea they didn't come up with on their own -- we call it the NIH (Not Invented Here) syndrome. But each to his own. Enjoy tonight's Balanis. You can save the Kraus for a special occasion. Roy Lewallen, W7EL |
Antenna reception theory
Roy Lewallen wrote:
But some people just can't deal with any idea they didn't come up with on their own ... You mean like Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(a) ? :-) The first time I saw that equation was in Dr. Best's QEX article. -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Roy Lewallen wrote:
In the process of confirming the 0.5 volt value, I found an error in a popular text, Balanis, _Antenna Theory, Analysis and Design_. On p. 61, he incorrectly states that the current along a short dipole "can be assumed to be constant", which isn't true, ... You must have the 1st edition. In the second edition Balanis says on page 133 that the current on an infinitesimal dipole can be considered to be constant. On page 143 he says the current along a small dipole is triangular shaped. -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Richard,
Terman said no such thing, and your interpretation is clearly in error. Magnetic fields cannot impart ANY energy to charges, such as electrons in a wire. This is because the force from a magnetic field on a charge is always perpendicular to the motion of the charge. No work can be done by the magnetic field, and the energy of the electrons does not change. Only electric fields can provide energy to an electron. Fortunately, Faraday's Law saves the day. Changing magnetic flux is inextricably intertwined with electromotive force. Terman's comment on page 2 of the 1955 edition simply points out the operation of Faraday's Law. (Yes, I have this volume of Terman.) Your conclusion statement is completely reversed. The magnetic field does nothing to induce current in the antenna, while the electric field does everything. Again, however, the laws of physics save the day. Maxwell's equations link electric and magnetic fields in such a manner that the magnetic field you favor creates just enough electric field to drive the electrons in the wire. As has been stated many times in this newsgroup, it is not possible to filter out one field component or the other. As long as there is some time dependence, i.e., other than purely static fields, both the electric and magnetic fields coexist. 73, Gene W4SZ Richard Harrison wrote: Roy Lewallen wrote: "You can find the explanation for why this is in any electromagnetic text." I found it in Terman. As we all know, we place correctly polarized dipoles, for example, parallel to the wavefront for maximum response. Terman confirms the electric field in this instance induces no energy in the antenna. It all comes from the magnetic field. If antenna current flows, no matter where it comes from, loss resistance causes a voltge drop. That`s why the wire needs to be perfect. The electric field produces no voltage in the antenna because the wavefront has the same voltage across its entire surface. That`s because it all left the same point at the same time. So, a wire parallel to the front has no difference of potential induced by the wavefront`s electric field. It all must come from the mgnetic field. On page 2 of his 1955 edition, Terman says: "The strength of the wave measured in terms of microvolts per meter of stress in space is also exactly the same voltage that the MAGNETIC FLUX (my emphasis) of the wave induces in a conductor 1 m long when sweeping across this conductor with the velocity of light." From the above, it is seen that the electric field is not effective in inducing current in a receiving antenna parallel to a wavefront. All the energy intercepted by the antenna is induced by the magnetic field. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
Cecil Moore wrote:
Roy Lewallen wrote: But some people just can't deal with any idea they didn't come up with on their own ... You mean like Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(a) ? :-) The first time I saw that equation was in Dr. Best's QEX article. Yes, and you didn't believe it when you saw it. 73, Tom Donaly, KA6RUH |
Antenna reception theory
Tom Donaly wrote:
Cecil Moore wrote: You mean like Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(a) ? :-) The first time I saw that equation was in Dr. Best's QEX article. Yes, and you didn't believe it when you saw it. Your memory is slightly faulty. What I objected to was Dr. Best's assertion that 75w + 8.33w = 133.33w. It still doesn't, never did, never will, and violates the conservation of energy principle. What Dr. Best apparently failed to realize is that the extra 50 watts of energy required to balance that energy equation does NOT come from waves P1 and P2 but instead comes from wave cancellation of waves P3 and P4 on the source side of the match point. Wave P1 contains 75 watts and Wave P2 contains 8.33 watts. Without a source of constructive interference energy, they cannot add up to 133.33 watts. That source is destructive interference energy, -2*SQRT(P3*P4), from the source side of the match point which supplies the +2*SQRT(P1*P2) constructive interference energy to the load side of the match point where (P1*P2)=(P3*P4). At an impedance discontinuity in a transmission line, far away from any source, all constructive interference energy must necessarily be balanced by an equal magnitude of destructive interference energy in order to satisfy the conservation of energy principle. This is all explained in my "WorldRadio", Oct./Dec. 2005 articles. Unfortunately, most of the Greek letter Thetas didn't make it through the conversion process and wound up as underline marks. Part I is already on my web page under "The Rest of the Story" along with a couple of remarks about forward power, reflected power, superposition, and interference. Part II will appear on my web page after Christmas. -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Asimov wrote:
"An antenna is just a stationary probe in a moving E-field." Along some path in space there is an electric current which is changing. It is growing or it is shrinking. It is not constant.. This current as a result of its changes radiates electric and magnetic flux. The electric flux lines are are perpendicular to the current path. The magnetic flux lines encircle the current path. The flux is moving away from the current path at the speed of light. At a distant point these electric and magnetic flux lines arrive because they sustain each other during their long trip. There is an initial wavefront. It started as a spherical wavefront but has traveled so far that for practical purposes it is now a plane wave. In the wavefront there is an electric force which would attract or repel electrons but it has the same strength everywhere over the arriving wavefront. Therefore, wlectrons in a wire parallel to the wavefront are not moved along its length by the electric force. This force would only tend to move electrons from one side of the wire`s diameter to the other side of the same diameter. Our interest is in current along the length of the wire. However, the magnetic lines of force are sweping at the speed of light across the wire which parallels the wavefront. If the wire also parallels the direction of the current which generated the lux (is correctly polarized), it will experience a voltage induced all along its length. This induction is totally a result of the magnetic field. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
There are some serious errors in this explanation.
1. The source is not an "electric current which is changing". There is an EM field made up of photons. There are two theories describing this, one is a wave theory and the other is a particle theory. Neither one completely enplains the phenomenon. 2. There is no current and therefore there is no "current path". 3. The E and H aspects behave similarly, both are changing. The E domain is no different in that respect then the H domain. The E portion of this particle/wave phenomenon is as capable of transforming into a useful signal in the antenna the H portion is. Antennas can be either E devices or H devices. E devices respond to the electric dimension and create a signal while H devices respond to the magnetic dimension and create a signal. Dan Richard Harrison wrote: Asimov wrote: "An antenna is just a stationary probe in a moving E-field." Along some path in space there is an electric current which is changing. It is growing or it is shrinking. It is not constant.. This current as a result of its changes radiates electric and magnetic flux. The electric flux lines are are perpendicular to the current path. The magnetic flux lines encircle the current path. The flux is moving away from the current path at the speed of light. At a distant point these electric and magnetic flux lines arrive because they sustain each other during their long trip. There is an initial wavefront. It started as a spherical wavefront but has traveled so far that for practical purposes it is now a plane wave. In the wavefront there is an electric force which would attract or repel electrons but it has the same strength everywhere over the arriving wavefront. Therefore, wlectrons in a wire parallel to the wavefront are not moved along its length by the electric force. This force would only tend to move electrons from one side of the wire`s diameter to the other side of the same diameter. Our interest is in current along the length of the wire. However, the magnetic lines of force are sweping at the speed of light across the wire which parallels the wavefront. If the wire also parallels the direction of the current which generated the lux (is correctly polarized), it will experience a voltage induced all along its length. This induction is totally a result of the magnetic field. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
On Mon, 05 Dec 2005 07:05:09 -0800, dansawyeror
wrote: Antennas can be either E devices or H devices. Hi Dan, Only at D.C. and then it mocks the sense of what an antenna should be. 73's Richard Clark, KB7QHC |
Antenna reception theory
"Richard Harrison" bravely wrote to "All" (05 Dec 05 08:08:30)
--- on the heady topic of " Antenna reception theory" RH From: (Richard Harrison) RH Xref: core-easynews rec.radio.amateur.antenna:220833 [,,,] RH There is an initial wavefront. It started as a spherical wavefront but RH has traveled so far that for practical purposes it is now a plane RH wave. In the wavefront there is an electric force which would attract RH or repel electrons but it has the same strength everywhere over the RH arriving wavefront. Therefore, wlectrons in a wire parallel to the RH wavefront are not moved along its length by the electric force. This RH force would only tend to move electrons from one side of the wire`s RH diameter to the other side of the same diameter. Our interest is in RH current along the length of the wire. [,,,] There is a time varying voltage gradient in the E field too. Turn the wire around 90" then to find the E gradient. If the wire length is such that one end is positive while the other end is negative then charges will flow inbetween both ends. Anti-static spray won't work on an antenna. A*s*i*m*o*v .... My wife and I always hold hands. If I let go, she shops. |
Antenna reception theory
Cecil Moore wrote: Tom Donaly wrote: Cecil Moore wrote: You mean like Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(a) ? :-) The first time I saw that equation was in Dr. Best's QEX article. Yes, and you didn't believe it when you saw it. Wave P1 contains 75 watts and Wave P2 contains 8.33 watts. Without a source of constructive interference energy, they cannot add up to 133.33 watts. And obviously he still doesn't believe it, Gene. 73, ac6xg |
Antenna reception theory
Jim Kelley wrote:
Wave P1 contains 75 watts and Wave P2 contains 8.33 watts. Without a source of constructive interference energy, they cannot add up to 133.33 watts. And obviously he still doesn't believe it, Gene. Without the 2*SQRT(P1*P2)=50w constructive interference energy, 75w + 8.33w will *NEVER* add up to 133.33 watts. Dr. Best's equation, 75w + 8.33w = 133.33w, is superposition of powers which is not allowed AND a violation of the conservation of energy principle. You don't really support superposition of powers and violations of conservation of energy, do you?. If you furnish exactly 75 watts and your neighbor furnishes exactly 8.33 watts, can you power a 133.33 watt device? -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Gene, W4SZ wrote:
"Terman`s comment on page 2 of the 1955 edition simply points out the operation of Faraday`s Law." Faraday`s law says that, while the magnetic flux linked with a closed path loop or coil is changing, the closed path is the source of an electromotive force (voltage) whose magnitude depends only upon the rate of change of the flux through the path. If we cause an antenna to be surrounded by an altrernating magnetic field, a voltage will be induced in the antenna in accordance with Faraday`s law, This induced voltage is necessary and sufficient to account for all of the energy received by the antenna. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
Hi Jim,
I was going to try to stay out of this recurring silliness, but since you accidentally pulled me in I will add my spin. The only mistake made by Steve Best was allowing himself to get dragged by Cecil into the intellectual landfill. Yes, most people with rudimentary arithmetic skills would agree that 75 plus 8.33 does not equal 133.33. However, anyone even remotely familiar with waves would readily understand that the component waves Cecil loves to talk about are merely mathematical conveniences. It is entire possible to set up other model configurations, such as a combination of a one traveling wave and one standing wave. In order to make his model work, Cecil needs to invoke the mythical P3 and P4 on the source side of the reflection discontinuity. He never gets around to explaining how these two waves, which exactly cancel at all points in space and at all times, can contain any energy at all. The reason that most practitioners of wave models solve for the fields first and then worry about power or energy is: a - This procedure works correctly all the time. b - It avoids the problems created by analyzing fictitious extra components added for mathematical convenience but containing no physical reality. I do not expect to change Cecil's mind. Other than his own potential embarrassment from the silly publications in World Radio, his folly is harmless. 73, Gene W4SZ Jim Kelley wrote: Cecil Moore wrote: Tom Donaly wrote: Cecil Moore wrote: You mean like Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(a) ? :-) The first time I saw that equation was in Dr. Best's QEX article. Yes, and you didn't believe it when you saw it. Wave P1 contains 75 watts and Wave P2 contains 8.33 watts. Without a source of constructive interference energy, they cannot add up to 133.33 watts. And obviously he still doesn't believe it, Gene. 73, ac6xg |
Antenna reception theory
Gene, W4SZ write:
"As has been said many times on this newsgroup, it is not possible to filter out one field component or the other." Saying it does not make it so. Countless Faraday screens are at work removing the E-field component from electromagnetic waves. Faraday said that the voltage in a coupled circuit depends only on the rate of change of the magnetic flux through the circuit. He was refering to induced voltage. It was 1831 when Michael Faraday observed the interaction between primary and secondary coils in what was likely the world`s first transformer. Faraday made it himself and noted that the needle of a galvanometer connected across one coil deflected briefly whenever he connected or disconnected a battery across the other coil. |
Antenna reception theory
it is just as easy to remove the H-field from the wave as it is to
remove the E-field with a Faraday screen. To remove the H-field, one sure way is to completely enclose two coils so they are completely shielded from each other and all electromagnetic waves. Put the coils in separate metal cans. Put a tiny hole in each can. Conect one termial of each coil to its end of a coupling capcitor. Ground the other terminal of each coil.. Ground is the return path for the coils but it must run on the surfaces of the cans and through the tiny holes due to skin effect. Complete shielding removes the H-field as a coupling agent. Only E-field coupling is provided via the coupling capacitor. Best regards, Richard Harrison, KB5WZI |
Antenna reception theory
Cecil Moore wrote: Jim Kelley wrote: Wave P1 contains 75 watts and Wave P2 contains 8.33 watts. Without a source of constructive interference energy, they cannot add up to 133.33 watts. And obviously he still doesn't believe it, Gene. I should have said Tom. If I were Cecil I'd have blamed the error on my glasses or my advanced age. ;-) You don't really support superposition of powers and violations of conservation of energy, do you?. Depending on how high you keep your squelch set, you should already pretty well know what I think about those things. You're at least partially right though. Power does not superpose (because, for among other reasons, it doesn't move or propagate). The point you continue to miss is that power does not interfere either. Nor is it valid to take the square root of the product of two power numbers and claim that it turns around miraculously and goes the other direction. But that's what you've miguidedly presented to the readers of World Radio as fact. The irradiance equations are nevertheless correct because power goes as the square of the fields - which do of course superpose and interfere. The equations accurately describe the effect - the end result, the outcome, not necessarily the cause or the mechanism by which the result is achieved. Before we go any further (and it is my sincerest hope that we do not), I agree with Melles-Griot, Born and Wolf, Hecht, Jackson, and the other E&M and optics books. What I disagree with (and I'm sure given the opportunity so would the above mentioned authors) is some of your interpretation of the physical phenomenon they describe. 73, ac6xg |
Antenna reception theory
Gene Fuller wrote:
Yes, most people with rudimentary arithmetic skills would agree that 75 plus 8.33 does not equal 133.33. Too bad Dr. Best posted the equation: "Ptotal = 75w + 8.33w = 133.33w" on this newsgroup (and, thank goodness, left it out of his article) so he obviously disagreed with you at the time. He also said that interference had nothing to do with it. However, anyone even remotely familiar with waves would readily understand that the component waves Cecil loves to talk about are merely mathematical conveniences. It is entire possible to set up other model configurations, such as a combination of a one traveling wave and one standing wave. What happens at an impedance discontinuity given those circumstances? To find out, read my WorldRadio article, Part I of which is posted on my web page. Part II will be posted after Christmas. At the risk of raising your politically incorrect ire as I have done with this technical posting, MERRY CHRISTMAS!. In order to make his model work, Cecil needs to invoke the mythical P3 and P4 on the source side of the reflection discontinuity. He never gets around to explaining how these two waves, which exactly cancel at all points in space and at all times, can contain any energy at all. The answer is simple. Do waves contain any energy at all? Do waves that cancel contain any energy? If waves contain no energy, they cannot exist, and therefore are incapable of canceling. If they exist and cancel, they contained energy just before their cancellation. Any way you cut it, my approach is consistent with the laws of physics as enumerated in "Optics", by Hecht, and yours leads to a contradiction of those laws of physics. The reason that most practitioners of wave models solve for the fields first and then worry about power or energy is: a - This procedure works correctly all the time. Yes, it does. But optics engineers didn't have the luxury of dealing with voltages and currents. They had to solve the problem using powers. And they did exactly that decades ago. That RF engineers refuse to consider the laws of physics concerning EM waves developed by optics engineers is absolutely astounding to me. W7EL put it best, something to the effect that if it wasn't invented here, we don't want to hear it (even if it is right). But I daresay that Eugene Hecht knows much more about EM waves that you will ever know, given your closed mind. I do not expect to change Cecil's mind. Other than his own potential embarrassment from the silly publications in World Radio, his folly is harmless. You are just displaying your extreme ignorance, Gene. My "WorldRadio" article corrects some of the *conceptual* errors in Dr. Best's QEX article but otherwise contains the same equations as his article. If you disagree with me, you are also disagreeing with Dr. Best's equations, i.e. you are between a rock and a hard place. It is interesting that the very people who tell us not to worry about energy are the people who get so emotionally rabid when someone chooses to worry about energy like real-world physicists do. What do they possibly have to lose besides face, self-esteem, sleep, and their pseudo-religious guru status? :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Jim Kelley wrote:
I should have said Tom. If I were Cecil I'd have blamed the error on my glasses or my advanced age. ;-) Alzheimer's can certainly strike at your age, Jim. :-) My Dad was legally blind when he was my age so I'm ahead of the curve. You're at least partially right though. Power does not superpose (because, for among other reasons, it doesn't move or propagate). The point you continue to miss is that power does not interfere either. Here's a quote from my magazine article, Jim. If you would just cease and desist from your MF'ing ways (that's "mind", not "muther"), you might understand. Quote: ************************************************** ******************** "The words 'power flow' have been avoided even though that is a term of common usage. For the purposes of this paper, energy flows and power is a measure of that energy flowing at a fixed point or plane. Likewise, the EM fields in the waves do the interfering. Powers, treaded as scalars, are incapable of interference." ************************************************** ******************** But you already knew that's what I believe since I have been telling you exactly that in CAPITAL LETTERS for years now and even sent you an advance copy of my magazine article. I have never asserted the things you claim that I have. Hopefully, the readers will recognize you for what you are. The irradiance equations are nevertheless correct because power goes as the square of the fields - which do of course superpose and interfere. The equations accurately describe the effect - the end result, the outcome, not necessarily the cause or the mechanism by which the result is achieved. Where does the constructive interference energy come from, Jim? Hecht says that in the absence of energy from other sources, the constructive interference energy must be exactly matched by an equal amount of destructive interference. Please present your credentials that allows you to disagree with Eugene Hecht? Before we go any further (and it is my sincerest hope that we do not), I agree with Melles-Griot, ... No you don't, and your disagreement is more than obvious to any informed casual observer. You remind me of a fellow employee from the 70's. I asked him what he would do if his wife caught him in bed with his neighbor's wife (as I did) and he answered, "I'd just deny it." -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Cecil,
If this is name-dropping poker, I'll see your Hecht and raise with J.D. Jackson and Born & Wolf. But thanks for the education. After 40 years of obtaining multiple degrees in physics followed by working R&D in the optics field I guess I still need to seek out some "real-world physicists" to figure out that energy is indeed something to "worry about". I never would have imagined such a thing! 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Yes, most people with rudimentary arithmetic skills would agree that 75 plus 8.33 does not equal 133.33. Too bad Dr. Best posted the equation: "Ptotal = 75w + 8.33w = 133.33w" on this newsgroup (and, thank goodness, left it out of his article) so he obviously disagreed with you at the time. He also said that interference had nothing to do with it. However, anyone even remotely familiar with waves would readily understand that the component waves Cecil loves to talk about are merely mathematical conveniences. It is entire possible to set up other model configurations, such as a combination of a one traveling wave and one standing wave. What happens at an impedance discontinuity given those circumstances? To find out, read my WorldRadio article, Part I of which is posted on my web page. Part II will be posted after Christmas. At the risk of raising your politically incorrect ire as I have done with this technical posting, MERRY CHRISTMAS!. In order to make his model work, Cecil needs to invoke the mythical P3 and P4 on the source side of the reflection discontinuity. He never gets around to explaining how these two waves, which exactly cancel at all points in space and at all times, can contain any energy at all. The answer is simple. Do waves contain any energy at all? Do waves that cancel contain any energy? If waves contain no energy, they cannot exist, and therefore are incapable of canceling. If they exist and cancel, they contained energy just before their cancellation. Any way you cut it, my approach is consistent with the laws of physics as enumerated in "Optics", by Hecht, and yours leads to a contradiction of those laws of physics. The reason that most practitioners of wave models solve for the fields first and then worry about power or energy is: a - This procedure works correctly all the time. Yes, it does. But optics engineers didn't have the luxury of dealing with voltages and currents. They had to solve the problem using powers. And they did exactly that decades ago. That RF engineers refuse to consider the laws of physics concerning EM waves developed by optics engineers is absolutely astounding to me. W7EL put it best, something to the effect that if it wasn't invented here, we don't want to hear it (even if it is right). But I daresay that Eugene Hecht knows much more about EM waves that you will ever know, given your closed mind. I do not expect to change Cecil's mind. Other than his own potential embarrassment from the silly publications in World Radio, his folly is harmless. You are just displaying your extreme ignorance, Gene. My "WorldRadio" article corrects some of the *conceptual* errors in Dr. Best's QEX article but otherwise contains the same equations as his article. If you disagree with me, you are also disagreeing with Dr. Best's equations, i.e. you are between a rock and a hard place. It is interesting that the very people who tell us not to worry about energy are the people who get so emotionally rabid when someone chooses to worry about energy like real-world physicists do. What do they possibly have to lose besides face, self-esteem, sleep, and their pseudo-religious guru status? :-) |
Antenna reception theory
Richard,
OK, I will turn this right back at you. How do you know that the countless Faraday screens remove the E-field component from electromagnetic waves? "Saying it does not make it so." Yes, I understand they are used in broadcast transmission lines, and yes, I understand they take many lightning hits. Faraday screens are effective. How do you know that they also negate the fundamental properties of time-varying electric and magnetic fields as expressed by Maxwell's equations? 73, Gene W4SZ Richard Harrison wrote: Gene, W4SZ write: "As has been said many times on this newsgroup, it is not possible to filter out one field component or the other." Saying it does not make it so. Countless Faraday screens are at work removing the E-field component from electromagnetic waves. Faraday said that the voltage in a coupled circuit depends only on the rate of change of the magnetic flux through the circuit. He was refering to induced voltage. It was 1831 when Michael Faraday observed the interaction between primary and secondary coils in what was likely the world`s first transformer. Faraday made it himself and noted that the needle of a galvanometer connected across one coil deflected briefly whenever he connected or disconnected a battery across the other coil. |
Antenna reception theory
Gene Fuller wrote:
If this is name-dropping poker, I'll see your Hecht and raise with J.D. Jackson and Born & Wolf. Please post any contradiction of Hecht by your sources. That argument could get very interesting. To summarize: Constructive interference energy must come from somewhere in the real world. You seem to disagree. So where do you think constructive interference energy comes from? But thanks for the education. After 40 years of obtaining multiple degrees in physics followed by working R&D in the optics field ... If you are omniscient, please prove it. If you are not omniscient and still capable of learning, please admit it. The trouble with gurus is that they sincerely believe that they know everything already and therefore cannot possibly learn anything new. I'm still open to learning. How about you? ... I guess I still need to seek out some "real-world physicists" to figure out that energy is indeed something to "worry about". I never would have imagined such a thing! That's a really strange thing to admit, Gene, since a very large percentage of the physics community is dedicated to understanding where the energy was, is, and will be - down to an almost infinitessimally small amount. You definitely seem to be cast in the mold of the priests who put Galileo under house arrest. Are you comfortable with that position? -- 73, Cecil http://www.qsl.net/w5dxp |
Antenna reception theory
Cecil,
If you know anything about physics, you must know that energy is at the core of almost all physical analysis. Sorry that my message was too opaque for you. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: ... I guess I still need to seek out some "real-world physicists" to figure out that energy is indeed something to "worry about". I never would have imagined such a thing! That's a really strange thing to admit, Gene, since a very large percentage of the physics community is dedicated to understanding where the energy was, is, and will be - down to an almost infinitessimally small amount. You definitely seem to be cast in the mold of the priests who put Galileo under house arrest. Are you comfortable with that position? |
Antenna reception theory
A short while ago, I explained why your Faraday cage doesn't separate E
and H as you claim. Exactly the same explanation applies to this structure, but with E and H reversed. It locally modifies the E/H ratio but doesn't separate the field components and it certainly doesn't remove the E field as you claim. Roy Lewallen, W7EL Richard Harrison wrote: it is just as easy to remove the H-field from the wave as it is to remove the E-field with a Faraday screen. To remove the H-field, one sure way is to completely enclose two coils so they are completely shielded from each other and all electromagnetic waves. Put the coils in separate metal cans. Put a tiny hole in each can. Conect one termial of each coil to its end of a coupling capcitor. Ground the other terminal of each coil.. Ground is the return path for the coils but it must run on the surfaces of the cans and through the tiny holes due to skin effect. Complete shielding removes the H-field as a coupling agent. Only E-field coupling is provided via the coupling capacitor. Best regards, Richard Harrison, KB5WZI |
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