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Radiation from wire
When will a wire radiate?
Can we make an oscillator circuit to radiate by simply connecting its output to a long wire ? Where can I get suitable study material on net about the topic? |
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Can we make an oscillator circuit to radiate by simply connecting its
output to a long wire ? ============================ Congratulations - you have just re-invented the radio transmitter! ;o) |
Burn the witch!!
-- "Reg Edwards" wrote in message ... Can we make an oscillator circuit to radiate by simply connecting its output to a long wire ? ============================ Congratulations - you have just re-invented the radio transmitter! ;o) |
Thanks for your compliment
Your friend |
Lots of Thanks
And I know that your are unlike the GUY below you...... Can you please be more precise about the web resources ? Jean |
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Rick Frazier wrote:
A radiating wire is essentially an antenna. Typically, in popular use, wires or equivalent metallic structures are not automatically considered antennas unless they are intended to transmit or receive a specific frequency range. This tends to increase confusion for people learning about electromagnetic radiation. I'd also add that I think it's important to point out to people that quasi-static analysis leads you to regular electric and magnetic field coupling (e.g., capacitive couplers and transformers) and that -- at least in my opinion -- such pickup is not to be attributed to an 'antenna.' That is, antennas are intended to transmit or receive far field radiation, even though of course it's not like a wire can differentiate where its signal is going to or coming from. It's a pet peeve of mine when people talk about noise induced in systems start calling everything in sight an 'antenna' even when there's nothing involved that's a large fraction of the wavelength of the signals in question... technically perhaps they're correct, but it doesn't help much in trying to combat the problem. ---Joel Kolstad |
Joel Kolstad wrote:
"It`s a pet peeve of mine when people tak about noise induced in systems start calling everything in sight an "antenna" even when there is nothing involved that is a large fraction of a wavelength of the signal in question." Someone needs a word for something that radiates or intercepts r-f. No need to distinguish between launchers and receptors. They are all launchers regardless of intentions. Every receiving antenna re-radiates at least 1/2 of everything it receives. Could call an antenna a radiator but radiator has 8 letters instead of 7. Aerial has only 6 letters. An antenna does not have to be big. It can be as small as an "elemental doublet". Terman says about an antenna on page 864 of his 1955 edition: "This (elemental doublet) consists of a length "delta l" that is short compared with the wavelength "lambda", and which is assumed to have such large capacitance areas associated with each end that the current throughout the doublet everywhere has the same I." The definition above is for "the simplest wire radiator or antenna ---." Best regards, Richard Harrison, KB5WZI |
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Art Unwin, KB9MZ wrote:
"If you place some circuit close to a normal dipole the circuit will take some of the energy from the dipole via coupling such that the circuit will oscillate and reradiate at its resonant frequency or at a frequency determined by its particular coefficient of coupling." Not exactly.. To obtain continuous oscillation requires a gain equal to loss in a circuit and introduction from the output to the input of the circuit a sufficient fraction in the proper phase to reinforce signals in the circuit. An oscillator is likely to have its frequency affected by any external coupling. That`s a reason to shield an oscillator and to provide a buffer between its output and external circuitry. A characteristic of a radio wave is its amplitude and frequency lock to the generator which produces it. Subsequent mistreatment of the wave by its environment is usually incapable of altering its alternations. Best regards, Richard Harrison, KB5WZI |
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Art Unwin KB9MZ wrote:
If I have a loop circuit unconnected to a transmitter could it not oscillate under ideal conditions? Art, what is the power source? -- 73, Cecil, W5DXP |
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Locate a tuning fork. Mount it any way you please. Then check it from
time to time to see if it spontaneously begins a sustained ringing. As a mechanical engineer, you're well acquainted with the differential equations that describe the motion of a physical object that's been struck, for example a tuning fork. And you'll recall that the form of the solution is a decaying sinusoid. An antenna or other resonant circuit obeys the same equations and behaves the same way. In electrical parlance, this response to excitation is called "ringing", after the obvious physical equivalent. While a tuning fork or an antenna will ring if excited, an antenna won't spontaneously ring, or produce a sustained oscillation without an external source of power -- for exactly the same reasons a tuning fork won't. Roy Lewallen, W7EL Art Unwin KB9MZ wrote: Richard, If I have a loop circuit unconnected to a transmitter could it not oscillate under ideal conditions? If it can then would it not radiate at the frequency that it is resonant at as well as reradiate at the frequency of the energy input Regards Art |
Art Unwin, KB9MZ wrote:
"If I have a loop circuit unconnected to a transmitter could it not oscillate under ideal conditions?" Ideal conditions would require a source of energy to replenish losses in the loop circuit. The source has to be the same frequency as that consumed in operation of the loop. A loop like any conductor or circuit has a self-resonant frequency. At resonance, the conductor`s inductive and capacitive reactances cancel. This zero reactance leaves only resistance to limit current in the conductor. Some of the total resistance may be a coupled load, and some will be radiation resistance, which is the conductor`s loss of r-f energy to radiation. Some energy will be lost in conversion to heat at the surface of the conductor and perhaps other locations. At frequencies not too far from resonance, reactance of the wire rises so high that little current flows and the wire has little effect on anything. Broadcasters are faced with structures which arise near their antenna arrays. At times these are resonant at the broadcast frequency and if so they absorb and re-radiate energy distorting the station`s radiation pattern. The solution is usually simply applying something to the new structure to detune it from resonance at the broadcast frequency. If not very near resonance, the structure won`t pickup enough energy to cause trouble. Too much reactance to allow current flow. The hard fact that a structure must be near resonance to admit significant energy makes broadbanding an antenna by an appurtenance tuned to some frequency other than the fundamental frequency of the antenna challenging. One method that works is a combination of antennas resonant for all the desired frequencies. There are other methods to get a wire to accept current over a wide frequency range. Wave antennas are an example. But, standing wave antennas are the most common and these need resonance or thereabouts. Best regards, Richard Harrison, KB5WZI |
Cecil Moore wrote in message ...
Art Unwin KB9MZ wrote: If I have a loop circuit unconnected to a transmitter could it not oscillate under ideal conditions? Art, what is the power source? Wow, this brought forth a lot of comments to contemplate. Regarding your question. I was thinking of energy radiated by a nearby source such as another radiator with very loose coupling from which it gets energy, and current flows in the loop, I then reason that with energy being applied to the loop it will also create oscillation PLUS a emf feedback to the initiating energy scource which then also reacts giving a 'pulse' to continue oscillation as well as energy for radiation. I see the loop not only reradiating the initial frequency impinged upon it by the outside source but also a radiation at the frequency of oscillation somewhat similar to that seen in a receiver where the object is to bring the two frequencies together. Now I am not electrically based and I am also guilty of using wrong terms in my description but I am using the hobby to experiment and learn. Now I did play with such a set up and was able to see two frequencies on the 141T, Whether I interpreted correctly what I saw is another matter. Fortunately I am not teaching the subject or trying to make a living from it nor do I have a resume to protect which gives me the opportunity to speculate, play around with the hobby without the danger of being beheaded. That is what is great about this hobby, it accepts all, the curious and the appliance operators all of which are not frightened by showing their ignorance of the subject but trying just the same. If I thought I knew a bit about conjugate matches I would have participated in the other postings but that was really beyond my ken and interest so you lucked out there. Cheers Art |
Richard Clark wrote in message . ..
On 10 Oct 2003 08:06:45 -0700, (Art Unwin KB9MZ) wrote: Richard, If I have a loop circuit unconnected to a transmitter could it not oscillate under ideal conditions? If it can then would it not radiate at the frequency that it is resonant at as well as reradiate at the frequency of the energy input Regards Art Hi Art, Distinguish between what resonates and what oscillates. Passive circuits do not oscillate even though they support the flow of alternating current. If what you state above is correct then I am wrong since basically what I am descibing is a passive feedback circuitu Art The ideal conditions for oscillation is the presence of a power source, gain, and feedback. If any of the three is missing, then there is no oscillation. The ideal conditions for resonance is an external source of alternating current coupled to a system that is harmonically related. If that system has no harmonic relation, then there is no oscillation or resonation. ALL systems that support the flow of alternating current radiate. How well this is performed is called efficiency. You cannot change a frequency without a nonlinear interface (like a diode) or without the original excitation source containing spurs (illegal at the antenna). 73's Richard Clark, KB7QHC |
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Richard Clark wrote in message . ..
On 10 Oct 2003 19:55:02 -0700, (Art Unwin KB9MZ) wrote: I then reason that with energy being applied to the loop it will also create oscillation Hi Art, The term is resonation, not oscillation. 73's Richard Clark, KB7QHC Richard, At my stage of life where death would beat a formal education one must resort to individual thinking,after all the exclamation of Eureka came from a man in a bath and not from a studying classroom tho the latter is a more consistant way to succecces. There in my case is it not unexpected that reasoning and thus nomenclature would be different from the regimented norm. You may remember that I once referred to radio waves as pulses ( it generated mirth) because I saw the current curve as starting from zero and ending at zero where the regimented term that the current goes THRU zero and thus is a wave. I submit that both are correct. In a similar way an electrical engineer may well look at a leaking tap as a continuoes leak while another may see the results as a series of pulses as shown by the continous sccesion of pulses. Roy used a mechanical action to bolster his case against mine while J.H.Morecraft uses similar analogy to to bolster his case * If one does not strive to understand INTENT then learning and understanding is thrown away in favour of debate. A similar aproach was taken when I tried to describe my antenna which is nothing more than a T section plus tuner but engineered backward to form a number of complex circuits where lumped circuits can be divided up into lumped and distributed components and thus negate the need for a serparate tuner while attaining high radiation efficiency, this again is an example of individual thinking and manipulating the known via unconventional thinking which was thrown out by those educated under the normal format. and different nomenclature which thru out understandings and evolved into debate. So yes, my terms may be different but thinking and understanding should not be thrown out because of lack of conformity. So I must ask you to give some leeway to me and strive to understand intent Regards Art * Principles of Radio Communication Second Edition With special reference to The laws of oscillating circuits/ currents in coupled circuits,chapter 111 |
Richard
I broke my post down to a single questio and for the life of me I cannot deduce your position. The question: .......could it not oscillate under ideal conditions ? Yes or no. If 'NO' is it based on the terminology of 'oscillation' I am basing my thoughts on the law of reprocity i.e.energy can be changed but not destroyed. Best regardsand nothing personal intended Art (Richard Harrison) wrote in message ... Art Unwin, KB9MZ wrote: "If I have a loop circuit unconnected to a transmitter could it not oscillate under ideal conditions?" Ideal conditions would require a source of energy to replenish losses in the loop circuit. The source has to be the same frequency as that consumed in operation of the loop. A loop like any conductor or circuit has a self-resonant frequency. At resonance, the conductor`s inductive and capacitive reactances cancel. This zero reactance leaves only resistance to limit current in the conductor. Some of the total resistance may be a coupled load, and some will be radiation resistance, which is the conductor`s loss of r-f energy to radiation. Some energy will be lost in conversion to heat at the surface of the conductor and perhaps other locations. At frequencies not too far from resonance, reactance of the wire rises so high that little current flows and the wire has little effect on anything. Broadcasters are faced with structures which arise near their antenna arrays. At times these are resonant at the broadcast frequency and if so they absorb and re-radiate energy distorting the station`s radiation pattern. The solution is usually simply applying something to the new structure to detune it from resonance at the broadcast frequency. If not very near resonance, the structure won`t pickup enough energy to cause trouble. Too much reactance to allow current flow. The hard fact that a structure must be near resonance to admit significant energy makes broadbanding an antenna by an appurtenance tuned to some frequency other than the fundamental frequency of the antenna challenging. One method that works is a combination of antennas resonant for all the desired frequencies. There are other methods to get a wire to accept current over a wide frequency range. Wave antennas are an example. But, standing wave antennas are the most common and these need resonance or thereabouts. Best regards, Richard Harrison, KB5WZI |
Art Unwin, KB9MZ wrote:
"The question ....Could it oscillate under ideal conditions? Yes or no." A tuned loop can not "oscillate", that is, to continue repeating a cycle of motions with strict periodicity, if it does not have a continuing supply of the resonant frequency. Analogies pose problems, but a resonant device responds to a particular frequency and ignores others. A resonant-reed low-frequency indicator is a vivid analogy of a collection of tuned circuits. Only the resonant reed responds to excitation which is applied to all of the reeds. Likewise, a resonant loop must be excited at its resonant frequency to accept and re-radiate energy. A collection of dipoles and loops may be exposed to r-f. If one of the collection is resonant, it accepts energy and re-radiates. A common inference from the word oscillation is production of continuous waves. The device making the oscillation is called an oscillator. I`ve seen loops and I`ve seen oscillators, and a loop without an active circuit is no oscillator. Best regards, Richard Harrison, KB5WZI |
Thanks for the posting Richard
I concede..... I had thought that the 'too and fro' of the 'coupling' would have continued after energy was turned off, like an ever changing EMF until final decrement. If this were true then I am sure an expert would have piped up. Since they didn't think the same way the energy decay (Current flow) must have been 'instantaneous' As I am not going to try for a ELECTRICAL degree as suggested ( O.K. I am a wimp )I am resigned to falling down a few times if I wish to move forward. At my age I don't get to move that fast anyway Best Regards Art (Richard Harrison) wrote in message ... Art Unwin, KB9MZ wrote: "The question ....Could it oscillate under ideal conditions? Yes or no." A tuned loop can not "oscillate", that is, to continue repeating a cycle of motions with strict periodicity, if it does not have a continuing supply of the resonant frequency. Analogies pose problems, but a resonant device responds to a particular frequency and ignores others. A resonant-reed low-frequency indicator is a vivid analogy of a collection of tuned circuits. Only the resonant reed responds to excitation which is applied to all of the reeds. Likewise, a resonant loop must be excited at its resonant frequency to accept and re-radiate energy. A collection of dipoles and loops may be exposed to r-f. If one of the collection is resonant, it accepts energy and re-radiates. A common inference from the word oscillation is production of continuous waves. The device making the oscillation is called an oscillator. I`ve seen loops and I`ve seen oscillators, and a loop without an active circuit is no oscillator. Best regards, Richard Harrison, KB5WZI |
Thanks for the posting Richard
I concede..... I had thought that the 'too and fro' of the 'coupling' would have continued after energy was turned off, like an ever changing EMF until final decrement. If this were true then I am sure an expert would have piped up. Since they didn't think the same way the energy decay (Current flow) must have been 'instantaneous' As I am not going to try for a ELECTRICAL degree as suggested ( O.K. I am a wimp )I am resigned to falling down a few times if I wish to move forward. At my age I don't get to move that fast anyway Best Regards Art (Richard Harrison) wrote in message ... Art Unwin, KB9MZ wrote: "The question ....Could it oscillate under ideal conditions? Yes or no." A tuned loop can not "oscillate", that is, to continue repeating a cycle of motions with strict periodicity, if it does not have a continuing supply of the resonant frequency. Analogies pose problems, but a resonant device responds to a particular frequency and ignores others. A resonant-reed low-frequency indicator is a vivid analogy of a collection of tuned circuits. Only the resonant reed responds to excitation which is applied to all of the reeds. Likewise, a resonant loop must be excited at its resonant frequency to accept and re-radiate energy. A collection of dipoles and loops may be exposed to r-f. If one of the collection is resonant, it accepts energy and re-radiates. A common inference from the word oscillation is production of continuous waves. The device making the oscillation is called an oscillator. I`ve seen loops and I`ve seen oscillators, and a loop without an active circuit is no oscillator. Best regards, Richard Harrison, KB5WZI |
Thanks for the posting Richard
I concede..... I had thought that the 'too and fro' of the 'coupling' would have continued after energy was turned off, like an ever changing EMF until final decrement. If this were true then I am sure an expert would have piped up. Since they didn't think the same way the energy decay (Current flow) must have been 'instantaneous' As I am not going to try for a ELECTRICAL degree as suggested ( O.K. I am a wimp )I am resigned to falling down a few times if I wish to move forward. At my age I don't get to move that fast anyway Best Regards Art (Richard Harrison) wrote in message ... Art Unwin, KB9MZ wrote: "The question ....Could it oscillate under ideal conditions? Yes or no." A tuned loop can not "oscillate", that is, to continue repeating a cycle of motions with strict periodicity, if it does not have a continuing supply of the resonant frequency. Analogies pose problems, but a resonant device responds to a particular frequency and ignores others. A resonant-reed low-frequency indicator is a vivid analogy of a collection of tuned circuits. Only the resonant reed responds to excitation which is applied to all of the reeds. Likewise, a resonant loop must be excited at its resonant frequency to accept and re-radiate energy. A collection of dipoles and loops may be exposed to r-f. If one of the collection is resonant, it accepts energy and re-radiates. A common inference from the word oscillation is production of continuous waves. The device making the oscillation is called an oscillator. I`ve seen loops and I`ve seen oscillators, and a loop without an active circuit is no oscillator. Best regards, Richard Harrison, KB5WZI |
Thanks for the posting Richard
I concede..... I had thought that the 'too and fro' of the 'coupling' would have continued after energy was turned off, like an ever changing EMF until final decrement. If this were true then I am sure an expert would have piped up. Since they didn't think the same way the energy decay (Current flow) must have been 'instantaneous' As I am not going to try for a ELECTRICAL degree as suggested ( O.K. I am a wimp )I am resigned to falling down a few times if I wish to move forward. At my age I don't get to move that fast anyway Best Regards Art (Richard Harrison) wrote in message ... Art Unwin, KB9MZ wrote: "The question ....Could it oscillate under ideal conditions? Yes or no." A tuned loop can not "oscillate", that is, to continue repeating a cycle of motions with strict periodicity, if it does not have a continuing supply of the resonant frequency. Analogies pose problems, but a resonant device responds to a particular frequency and ignores others. A resonant-reed low-frequency indicator is a vivid analogy of a collection of tuned circuits. Only the resonant reed responds to excitation which is applied to all of the reeds. Likewise, a resonant loop must be excited at its resonant frequency to accept and re-radiate energy. A collection of dipoles and loops may be exposed to r-f. If one of the collection is resonant, it accepts energy and re-radiates. A common inference from the word oscillation is production of continuous waves. The device making the oscillation is called an oscillator. I`ve seen loops and I`ve seen oscillators, and a loop without an active circuit is no oscillator. Best regards, Richard Harrison, KB5WZI |
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