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transmission lines and SWR and fractional wave antennas
When measuring the SWR of a transmission line we can find a length
that is resonant. Or in other words the current is of an exact sinusoidal form and thus the basis of SWR. When we apply the same principles to a radiator we cannot assume a perfect sinusoidal wave because of the field generated outside the radiator where a degradation of amplitude depends not only on the generated fields but also the length of the radiator i.e a thin radiator. Thus one can see that a fractional wave antenna if reflected as generally assumed cannot possibly be 1:1 for a wavelength as per a perfect reflection as could or would be seen from a transmississsion line. The above not only shows that a transmission line is a closed circuit as is a fractional wavelength antenna where the current travels on the inside of the radiator and where the transmission line has current flow on the inside of the outer skin (brading) The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. It should be seen that when we use the term SWR we are looking at two different things, a transmission line which is not radiating( ignoring leakage) but still a closed circuit and a radiator that is radiating but with a non sinusoidal current which is contrary to the assumptions made for MoM style radiator programs. Thus it should be seen that any radiator is a closed circuit with continuous leakage in current levels dependent on its length via accountability for all four fouces present.. Regards Art |
transmission lines and SWR and fractional wave antennas
"Art Unwin" wrote in message ... When measuring the SWR of a transmission line we can find a length that is resonant. Or in other words the current is of an exact sinusoidal form and thus the basis of SWR. When we apply the same principles to a radiator we cannot assume a perfect sinusoidal wave because of the field generated outside the radiator where a degradation of amplitude depends not only on the generated fields but also the length of the radiator i.e a thin radiator. Thus one can see that a fractional wave antenna if reflected as generally assumed cannot possibly be 1:1 for a wavelength as per a perfect reflection as could or would be seen from a transmississsion line. The above not only shows that a transmission line is a closed circuit as is a fractional wavelength antenna where the current travels on the inside of the radiator and where the transmission line has current flow on the inside of the outer skin (brading) The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. It should be seen that when we use the term SWR we are looking at two different things, a transmission line which is not radiating( ignoring leakage) but still a closed circuit and a radiator that is radiating but with a non sinusoidal current which is contrary to the assumptions made for MoM style radiator programs. Thus it should be seen that any radiator is a closed circuit with continuous leakage in current levels dependent on its length via accountability for all four fouces present.. Regards Art The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; it computes the current distribution. The radiated field is then calculated based on the current distribution. Frank |
transmission lines and SWR and fractional wave antennas
"Frank" wrote in message news:toE5l.932$z%.775@edtnps82... "Art Unwin" wrote in message ... When measuring the SWR of a transmission line we can find a length that is resonant. Or in other words the current is of an exact sinusoidal form and thus the basis of SWR. When we apply the same principles to a radiator we cannot assume a perfect sinusoidal wave because of the field generated outside the radiator where a degradation of amplitude depends not only on the generated fields but also the length of the radiator i.e a thin radiator. Thus one can see that a fractional wave antenna if reflected as generally assumed cannot possibly be 1:1 for a wavelength as per a perfect reflection as could or would be seen from a transmississsion line. The above not only shows that a transmission line is a closed circuit as is a fractional wavelength antenna where the current travels on the inside of the radiator and where the transmission line has current flow on the inside of the outer skin (brading) The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. It should be seen that when we use the term SWR we are looking at two different things, a transmission line which is not radiating( ignoring leakage) but still a closed circuit and a radiator that is radiating but with a non sinusoidal current which is contrary to the assumptions made for MoM style radiator programs. Thus it should be seen that any radiator is a closed circuit with continuous leakage in current levels dependent on its length via accountability for all four fouces present.. Regards Art The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; it computes the current distribution. The radiated field is then calculated based on the current distribution. Frank art doesn't know MOM from the fractal least squares genetic optimizer code... so don't be surprised when he comes back with more gibberish. |
transmission lines and SWR and fractional wave antennas
On Dec 27, 11:46*pm, "Frank" wrote:
"Art Unwin" wrote in message ... When measuring the SWR of a transmission line we can find a length that is resonant. Or in other words the current is of an exact sinusoidal form and thus the basis of SWR. When we apply the same principles to a radiator we cannot assume a perfect sinusoidal wave because of the field generated outside the radiator where a degradation of amplitude depends not only on the generated fields but also the length of the radiator i.e a thin radiator. Thus one can see that a fractional wave antenna if reflected as generally assumed cannot possibly be 1:1 for a wavelength as per a perfect reflection as could or would be seen from a transmississsion line. The above not only shows that a transmission line is a closed circuit as is a fractional wavelength antenna where the current travels on the inside of the radiator and where the transmission line has current flow on the inside of the outer skin (brading) The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. It should be seen that when we use the term SWR we are looking at two different things, a transmission line which is not radiating( ignoring leakage) but still a closed circuit and a radiator that is radiating but with a non sinusoidal current which is contrary to the assumptions made for MoM style radiator programs. Thus it should be seen that any radiator is a closed circuit with continuous leakage in current levels dependent on its length via accountability for all four fouces present.. Regards Art The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; *it computes the current distribution. The radiated field is then calculated based on the current distribution. Frank Yes it does but as always one must review the basis on which formula is formed and conditions expressed One of these conditions is that current flow is sinusoidal which cannot be true because of leakage ( radiation) per unit length of the radiator. If on compares the current flow of a full wave radiatior to a fractional wave current flow this becomes very obvious especially when either of them is compared to a true sino soidal curve Cheers Frank |
transmission lines and SWR and fractional wave antennas
On Dec 28, 8:20*am, "Dave" wrote:
"Frank" wrote in message news:toE5l.932$z%.775@edtnps82... "Art Unwin" wrote in message ... When measuring the SWR of a transmission line we can find a length that is resonant. Or in other words the current is of an exact sinusoidal form and thus the basis of SWR. When we apply the same principles to a radiator we cannot assume a perfect sinusoidal wave because of the field generated outside the radiator where a degradation of amplitude depends not only on the generated fields but also the length of the radiator i.e a thin radiator. Thus one can see that a fractional wave antenna if reflected as generally assumed cannot possibly be 1:1 for a wavelength as per a perfect reflection as could or would be seen from a transmississsion line. The above not only shows that a transmission line is a closed circuit as is a fractional wavelength antenna where the current travels on the inside of the radiator and where the transmission line has current flow on the inside of the outer skin (brading) The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. It should be seen that when we use the term SWR we are looking at two different things, a transmission line which is not radiating( ignoring leakage) but still a closed circuit and a radiator that is radiating but with a non sinusoidal current which is contrary to the assumptions made for MoM style radiator programs. Thus it should be seen that any radiator is a closed circuit with continuous leakage in current levels dependent on its length via accountability for all four fouces present.. Regards Art The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; *it computes the current distribution. The radiated field is then calculated based on the current distribution.. Frank art doesn't know MOM from the fractal least squares genetic optimizer code... so don't be surprised when he comes back with more gibberish. David there is nothing technical to respond to in your posting so what sort of response were you looking for?. If MoM has the condition stated in the ARRL compendium then something is seriously wrong with antenna programs! Regards Art |
transmission lines and SWR and fractional wave antennas
The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current distribution. The radiated field is then calculated based on the current distribution. Frank Yes it does but as always one must review the basis on which formula is formed and conditions expressed One of these conditions is that current flow is sinusoidal which cannot be true because of leakage ( radiation) per unit length of the radiator. If on compares the current flow of a full wave radiatior to a fractional wave current flow this becomes very obvious especially when either of them is compared to a true sino soidal curve Cheers Frank None of the conditions assume current (distribution) on a radiator is sinusoidal. It can be anything, not even remotely sinusoidal, and frequently has discontinuities (such as a "unit step function" in the case of a shunt fed, gamma matched, grounded tower, for example). The theory behind the "Moment method", in the case of NEC 2, is in the public domain, and available he http://www.nec2.org/other/nec2prt1.pdf Frank |
transmission lines and SWR and fractional wave antennas
On Dec 28, 11:06*am, "Frank" wrote:
The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; it computes the current distribution. The radiated field is then calculated based on the current distribution. |
transmission lines and SWR and fractional wave antennas
"Art Unwin" wrote in message ... Using just one example radiation at present is presumed to provide many waves along a conductor purely on the bases that current is reflected from the antenna end and progresses along the same path that it arrived. This error alone has allowed many assumptions and erronious theories to be expanded. oh no! now he doesn't believe in reflections! how could we ever survive on here without endless discussions of reflections and waves? |
transmission lines and SWR and fractional wave antennas
"Art Unwin" wrote
The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. _____________ Art, the current distribution along even the shortest (fractional wavelength), constant OD radiator also is ~sinusoidal. Currrent always is near zero at the open end of a linear radiator of every physical length. The shape of the current wave formed along a very short radiator appears to be very close to triangular. But in fact that "triangular" current distribution is just a very short section of a sinusoidal waveform. N.B. that MoM programs show exactly this for radiators that are very short in terms of electrical wavelengths. This also is proven mathematically in the antenna engineering textbooks of Kraus, Balanis, Johnson & Jasik, etc etc. RF ** Posted from http://www.teranews.com ** |
transmission lines and SWR and fractional wave antennas
"Art Unwin" wrote
The antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. _____________ Art, the current distribution along even the shortest fractional wavelength, constant OD radiator also is ~sinusoidal. Current always is near zero at the open end of a linear radiator of every physical length. The shape of the current wave formed along a very short radiator appears to be very close to triangular. But in fact that "triangular" current distribution is just a very short section of a sinusoidal waveform. N.B. that MoM programs show exactly this for radiators that are very short in terms of electrical wavelengths. This also is proven mathematically in the antenna engineering texts of Kraus, Balanis, Johnson & Jasik, etc. RF |
transmission lines and SWR and fractional wave antennas
On Dec 28, 12:36*pm, Richard Fry wrote:
"Art Unwin" wroteThe antenna compendium states that an assumption is made with MoM programs that an assumption is made that current in a radiator is sinusoidal where as we all know that the current degrades in aplitude dependent on radiator length. _____________ Art, the current distribution along even the shortest fractional wavelength, constant OD radiator also is ~sinusoidal. Current always is near zero at the open end of a linear radiator of every physical length. The shape of the current wave formed along a very short radiator appears to be very close to triangular. *But in fact that "triangular" current distribution is just a very short section of a sinusoidal waveform. N.B. that MoM programs show exactly this for radiators that are very short in terms of electrical wavelengths. *This also is proven mathematically in the antenna engineering texts of Kraus, Balanis, Johnson & Jasik, etc. RF O.K. have it your way. At the end of a radiator voltage is a maximum as current is zero ie the curves of current and current crosses each other. We can then use the absolute standard equatiion of E = I R. Using this formula for understanding conditions at the end of a radiator we can state that E, I and R equals zero ala a non closed circuit. Kraus used four travelling waves in his analysis of the helical antenna an analysis that was not corrobarated by following examiners or the application of the NEC (MoM) programs where disturbing differences was never resolved. You introduce wavelength as if it was a standard without considering the velocity factor and where a transmission line analogy does not satisfy a helical antenna because of slow wave created in a similar way to cavitation as explored by Bernoulle or by the addition of sharp corners encountered by current flow As far as what has been proven in text books they are only reflect the conditions placed on the problem but also assumption of correct theory applied. This is why history shows the evolution of science is a series of broken theories whose value is measured by their resistance to attack over time. I would remind you that the metric of time has NOT stopped. But as I stated earlier you can have it your way without objection from me Art |
transmission lines and SWR and fractional wave antennas
The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; it computes the current distribution. The radiated field is then calculated based on the current distribution. Frank Exactly correct. EZNEC (including demo) users can get a good illustration of this by looking at the pattern from the example file Cardioid.ez which consists of two identical elements with perfect spacing and perfectly ratioed base currents. Notice that the front/back ratio is about 35 dB (dropping to about 31 dB with more segments for more accurate results), while it should be essentially infinite. The small back lobe is caused by modification of the current distribution on the two elements caused by mutual coupling -- although the base currents are perfectly equal in magnitude and 90 degrees out of phase, the fields from the two elements aren't, due to their having slightly different current distributions. When I first saw this back lobe with perfectly ratioed base currents, I searched through the program code looking for what I was certain was a bug. I finally realized that the result was correct and that the lobe was caused by the altered current distribution which the program had correctly calculated. For more about this, see http://eznec.com/Amateur/Articles/Current_Dist.pdf. The assumption of sinusoidal current distribution is strictly true only with straight, isolated conductors which are infinitely thin, although it's a reasonably good assumption in many other cases. Mathematical analyses of antennas done before computers were pretty much limited to cases where sinusoidal distribution was assumed, because a more accurate determination of current distribution was virtually impossible to calculate. The ability to determine the actual current distribution is one of the very important advantages of computer analysis. Roy Lewallen, W7EL |
transmission lines and SWR and fractional wave antennas
Art wrote:
"We can then use the absolute standard equation of E = I R." For ac (RF) that`s not true. The formula is E=IZ, where Z includes reactance and resistance in quadrature. I`m not piling on but some readers may believe Art. Best regards, Ricxhard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
On Dec 28, 4:12*pm, (Richard Harrison)
wrote: Art wrote: "We can then use the absolute standard equation of E = I R." For ac (RF) that`s not true. The formula is E=IZ, where Z includes reactance and resistance in quadrature. I`m not piling on but some readers may believe Art. * Best regards, Ricxhard Harrison, KB5WZI Yes you are correct but the original equation was E=IR which preceeds the implication of impedance which is a derivative of my equation and came about with the addition of A.C. technology. If the impedance is totally resistive then my statement is not untrue Now to avoid the nitpicking are you saying that E=IZ cannot be used for calculations at the end of an antenna and if so" WHY " Art |
transmission lines and SWR and fractional wave antennas
Art wrote:
"Now to avoid nitpicking are you saying that E=IZ cannot be used for calculations at the end of an antenna and if so "WHY"?" It is complicated by multiple currents. Like an open-circuited transmission line, electrical conduction stops at the end of the conductor. Current then becomes a phasor problem. Collapse of conduction current induces a voltage which combined with the incident voltage almost doubles the total voltage at this spot in many cases. This reverses the direction of current in the conductor. Due to capacitance at his high-voltage spot with the iniverse, displacement current flows into free space from open-circuited antenna ends. It is usually smaller than the conduction current. Best regards, Richard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
On Dec 28, 3:32*pm, Roy Lewallen wrote:
The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; *it computes the current distribution. The radiated field is then calculated based on the current distribution.. Frank Exactly correct. EZNEC (including demo) users can get a good illustration of this by looking at the pattern from the example file Cardioid.ez which consists of two identical elements with perfect spacing and perfectly ratioed base currents. Notice that the front/back ratio is about 35 dB (dropping to about 31 dB with more segments for more accurate results), while it should be essentially infinite. The small back lobe is caused by modification of the current distribution on the two elements caused by mutual coupling -- although the base currents are perfectly equal in magnitude and 90 degrees out of phase, the fields from the two elements aren't, due to their having slightly different current distributions. When I first saw this back lobe with perfectly ratioed base currents, I searched through the program code looking for what I was certain was a bug. I finally realized that the result was correct and that the lobe was caused by the altered current distribution which the program had correctly calculated. For more about this, seehttp://eznec.com/Amateur/Articles/Current_Dist.pdf. The assumption of sinusoidal current distribution is strictly true only with straight, isolated conductors which are infinitely thin, although it's a reasonably good assumption in many other cases. Mathematical analyses of antennas done before computers were pretty much limited to cases where sinusoidal distribution was assumed, because a more accurate determination of current distribution was virtually impossible to calculate. The ability to determine the actual current distribution is one of the very important advantages of computer analysis. Roy Lewallen, W7EL If current distribution is calculated correctly as stated then the answer with respect to the route taken of the current of a fractional wave antenna should be available and beyond doubt as the program is derived from Maxwells laws. The distributed current should be DC based if current flow is thru the center of the radiator. As far as the resistance encountered on reverse flow on the outside of a radiator the figure provided by computor programs should be rather interesting as I have never encountered in print suggested figures. In accordance with some engineers the radiation resistance but be stated as the radiation impedance to avoid sniping Art |
transmission lines and SWR and fractional wave antennas
On Dec 28, 5:35*pm, (Richard Harrison)
wrote: Art wrote: "Now to avoid nitpicking are you saying that E=IZ cannot be used for calculations at the end of an antenna and if so "WHY"?" It is complicated by multiple currents. Like an open-circuited transmission line, electrical conduction stops at the end of the conductor. Current then becomes a phasor problem. Collapse of conduction current induces a voltage which combined with the incident voltage almost doubles the total voltage at this spot in many cases. This reverses the direction of current in the conductor. Due to capacitance at his high-voltage spot with the iniverse, displacement current flows into free space from open-circuited antenna ends. It is usually smaller than the conduction current. Best regards, Richard Harrison, KB5WZI You skated over the difference between an open circuit of the transmission line compared to the end of an antenna. The analogy is flawed and will be shown when the resistance in the center of a radiator is disclosed via the computor programs. You never did supply the information needed to justify the values of E,I and R when the current value crosses the zero line on a graph. You can ofcourse, declare that none of the given factors can ever be equal to zero by jumping the datum line !!!!! By the way, could you state a situation where the displacement current is LARGER than the conduction current so I may review it in the light of Newtonian laws? Art Art |
transmission lines and SWR and fractional wave antennas
"Roy Lewallen" wrote in message . .. The "Method of Moments" (MOM) makes no assumptions about current distribution on a radiator; it computes the current distribution. The radiated field is then calculated based on the current distribution. Frank Exactly correct. EZNEC (including demo) users can get a good illustration of this by looking at the pattern from the example file Cardioid.ez which consists of two identical elements with perfect spacing and perfectly ratioed base currents. Notice that the front/back ratio is about 35 dB (dropping to about 31 dB with more segments for more accurate results), while it should be essentially infinite. The small back lobe is caused by modification of the current distribution on the two elements caused by mutual coupling -- although the base currents are perfectly equal in magnitude and 90 degrees out of phase, the fields from the two elements aren't, due to their having slightly different current distributions. When I first saw this back lobe with perfectly ratioed base currents, I searched through the program code looking for what I was certain was a bug. I finally realized that the result was correct and that the lobe was caused by the altered current distribution which the program had correctly calculated. For more about this, see http://eznec.com/Amateur/Articles/Current_Dist.pdf. The assumption of sinusoidal current distribution is strictly true only with straight, isolated conductors which are infinitely thin, although it's a reasonably good assumption in many other cases. Mathematical analyses of antennas done before computers were pretty much limited to cases where sinusoidal distribution was assumed, because a more accurate determination of current distribution was virtually impossible to calculate. The ability to determine the actual current distribution is one of the very important advantages of computer analysis. Roy Lewallen, W7EL Thanks for the info. A very interesting link. I have experimented with NEC models of phased arrays, and found the same problem with a small back lobe. I followed the procedure in the ARRL Antenna book, which involved calculating the elements in a 2 X 2 complex Z matrix, for a 2 element phased dipole array. The results appeared to be very good, but I never actually built it. Frank, VE6CB |
transmission lines and SWR and fractional wave antennas
Art wrote:
"could you state a situation where the displacement current is LARGER than the conduction current so I may review it in the light of Newtonian laws?" I have difficulty in imagining current between the plates of a capacitor exceeding the current through the capacitor`s leads. Values of voltages and currents anywhere along an antenna primarily depend on the impedance of the antenna at that point and then are dictated by the phasors of the incident and reflected totals at the same point. Arnold B. Bailey in Fig. 7-28 on page 368 of "TV And Other Receiving Antennas" shows current distribution on a half-wave dipole which smoothly varies from zero at its ends to maximum at its center. Experience shows that a quarter-wave back from a maximum impedance point, a minimum impedance point is created by incident and reflected phasors. Best regards, Richard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
In article , Roy
Lewallen wrote: The assumption of sinusoidal current distribution is strictly true only with straight, isolated conductors which are infinitely thin, although it's a reasonably good assumption in many other cases. Mathematical analyses of antennas done before computers were pretty much limited to cases where sinusoidal distribution was assumed, because a more accurate determination of current distribution was virtually impossible to calculate. The ability to determine the actual current distribution is one of the very important advantages of computer analysis. Roy Lewallen, W7EL Hello, Roy, and while the above is certainly correct, you're probably wasting your time. Many folks like to fashion their own "reasonable" explanations even when they're completely off track (should I mention the CFA again?). Of course they're always right and it's the rest of the world who's wrong. Certain folks on this ng appear to be in constant need of validation. Persons without some knowledge of the underlying physics and applied math are destined to reach the wrong conclusions IMO. Of course that's not going to stop some from building a CFA because as we all know it's the standard comms antenna used at the Groom Lake facility to keep in touch with Klaatu. Sincerely, and 73s from N4GGO, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
transmission lines and SWR and fractional wave antennas
Art Unwin wrote:
You never did supply the information needed to justify the values of E,I and R when the current value crosses the zero line on a graph. In simple terms, when the standing-wave current has a zero amplitude at a current node, none of the energy is in the magnetic field and all of the energy is in the electric field. That's why a voltage maximum appears at a current minimum. When the current equals zero, the virtual impedance, E/I, is infinite. This is essentially what happens at the end of a dipole or monopole or open-circuit stub. The characteristic impedance of a #14 wire 30 feet above ground is very close to 600 ohms. Given that Z0, we can treat a dipole element as a lossy transmission line and calculate the voltage at the end of the dipole element. If we model a 1/4WL 600 ohm open-circuit stub with EZNEC and adjust the resistivity to 0.0000021 ohm-m to simulate the radiation resistance of a dipole wire, the feedpoint impedance of the stub is 35 ohms and conditions on the lossy stub are very close to the conditions on a dipole element. -- 73, Cecil http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
On Dec 29, 9:11*am, Cecil Moore wrote:
Art Unwin wrote: You never did supply the information needed to justify the values of E,I and R when *the current value crosses the zero line on a graph. In simple terms, when the standing-wave current has a zero amplitude at a current node, none of the energy is in the magnetic field and all of the energy is in the electric field. That's why a voltage maximum appears at a current minimum. When the current equals zero, the virtual impedance, E/I, is infinite. This is essentially what happens at the end of a dipole or monopole or open-circuit stub. The characteristic impedance of a #14 wire 30 feet above ground is very close to 600 ohms. Given that Z0, we can treat a dipole element as a lossy transmission line and calculate the voltage at the end of the dipole element. If we model a 1/4WL 600 ohm open-circuit stub with EZNEC and adjust the resistivity to 0.0000021 ohm-m to simulate the radiation resistance of a dipole wire, the feedpoint impedance of the stub is 35 ohms and conditions on the lossy stub are very close to the conditions on a dipole element. -- 73, Cecil *http://www.w5dxp.com At the end of the radiator you state the energy is transfered to the field so I would imagine there is zero skin effect at that point and the chain of skin effect is still present on the outside of the radiator, this because a full period has not yet elapsed This equates to a displacement current across the capacitance gap (plates) between the outside and the inside of the radiator which is the only current route available when the capacitor field expires. Note that this energy is released prior to the end of the current flow period because of the absence of the skin effect at that time. Cecil I am examining all the holy cows that pervade the science of radiation as it is universally accepted that radiation is not fully understood, thus the many hats! At the moment I see no mechanism that supports the capacitor field to expire in the direction of incoming current prior to the completion of the forward period. Regards Art |
transmission lines and SWR and fractional wave antennas
Art Unwin wrote:
At the moment I see no mechanism that supports the capacitor field to expire in the direction of incoming current prior to the completion of the forward period. The "capacitive" field is the *electric* field which is at a *maximum* amplitude at the tip of a dipole. It is the magnetic (inductive) field that is close to zero at the tip of a dipole. -- 73, Cecil http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
On Dec 29, 10:26*am, Cecil Moore wrote:
Art Unwin wrote: At the moment I see no mechanism that supports the capacitor field to expire in the direction of incoming current prior to the completion of the forward period. The "capacitive" field is the *electric* field which is at a *maximum* amplitude at the tip of a dipole. It is the magnetic (inductive) field that is close to zero at the tip of a dipole. -- 73, Cecil *http://www.w5dxp.com Cecil I still am looking for an explanation that prevents current flow thru the center. I recognise that the common thinking is to accept reflection but I fail to see how that can happen so I can follow up with the numbers. The capacitor is limited with respect to the energy that it can retain so what happens when that limit is reached and the forward period has not come to an end? Yes, the common thinking is that the current changes direction to oppose the forward moving current as with a reflection where the eddy current in the reverse direction cancels the eddy current moving in the other direction. It is here that I am looking for a mechanism that justifies this reasoning of reflection so I can begin to dispel the closed circuit aproach as seen with a full wave radiator in equilibrium Best regards Art Art but I am looking for actual proof |
transmission lines and SWR and fractional wave antennas
Art wrote:
"The capacitor is limited with respect to energy it can retain so what happens when that limit is reached and the forward period has not come to an end?" There is a sudden flash as energy jumps the gap between the plates. The energy a capacitor can store expressed in joules is equal to its capacitance in microfarads times the voltage (squared) across its plates divided by two million. For a fixed capacitor, the only vatiable is the voltage. So, the greater the voltage across the capacitor the greater the energy it stores. The only limit is the breakdown voltage. Best regards, Richard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
On Dec 29, 12:25*pm, (Richard Harrison)
wrote: Art wrote: "The capacitor is limited with respect to energy it can retain so what happens when that limit is reached and the forward period has not come to an end?" There is a sudden flash as energy jumps the gap between the plates. The energy a capacitor can store expressed in joules is equal to its capacitance in microfarads times the voltage (squared) across its plates divided by two million. For a fixed capacitor, the only vatiable is the voltage. So, the greater the voltage across the capacitor the greater the energy it stores. The only limit is the breakdown voltage. Best regards, Richard Harrison, KB5WZI So one acknowledges the presence of a capacitor at the end of a radiator So now we determine the capacitance and the voltage withstand together with what comprises as a capacitor at the end of a radiator to relate to which way the current flows. The question with respect to current flow is still present and unanswered despite all of the manouvaring the face the question head on. If the past means anything this subject could go to a 1000 posts with neither a modicom of science to bolster the talk Art |
transmission lines and SWR and fractional wave antennas
I still am looking for an explanation that prevents current flow thru
the center. Well, being a logical person, I would ask what mechanism of physics keeps the forward current from flowing through the center to start with? Why doesn't the forward current flow through the center and the reflected current flow back on the surface? Whatever that mechanism is, it seems logical to conclude that it might also prevent reflected current from flowing back through the center. If we put a signal generator at each end of a wire, which current flows on the outside and which flows on the inside? -- 73, Cecil http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
Art wrote:
"Yes, the common thinking is that current changes direction to oppose the forward moving current as with a reflection where the eddy current moving in the reverse direction cancels the eddy current moving in the other direction." Transformers are laminated to reduce eddy current core losses. Reverse currents on a transmission line or on an antenna are usually called the reflected current. Reflections are caused by discontinuities in the path of the EM wave. In the case of an open circuit, the reflection coefficient is infinite and the incident and reflected waves have the same magnitude and phase. The voltage at the discontinuity is thus doubled. See Terman`s 1955 opus page 89. But, the current goes to zero as conduction ends at the open circuit. No energy is lost in the open circuit. It is just concentrated in the electric field as the magnetic field loses its energy. Best regards, Richard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
Art Unwin wrote:
So one acknowledges the presence of a capacitor at the end of a radiator Let's use IEEE definitions to avoid confusion. A "capacitor" is a physical component that exhibits capacitance. Capacitance can be exhibited without the existence of a physical lumped component. At the end of a radiator, we would have a distributed capacitance, not *a* lumped capacitor. And actually, it is not only at the end since it is "distributed". In fact, an antenna element can be modeled as a distributed RLC network where the R includes all "losses" including radiation. -- 73, Cecil http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
Richard Harrison wrote:
In the case of an open circuit, the reflection coefficient is infinite Richard, I'll bet you know that the reflection coefficient is 1.0 for an open circuit and -1.0 for a short circuit.:-) -- 73, Cecil http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
J. B. Wood wrote:
Hello, Roy, and while the above is certainly correct, you're probably wasting your time. Many folks like to fashion their own "reasonable" explanations even when they're completely off track (should I mention the CFA again?). Of course they're always right and it's the rest of the world who's wrong. Certain folks on this ng appear to be in constant need of validation. Persons without some knowledge of the underlying physics and applied math are destined to reach the wrong conclusions IMO. Of course that's not going to stop some from building a CFA because as we all know it's the standard comms antenna used at the Groom Lake facility to keep in touch with Klaatu. Sincerely, and 73s from N4GGO, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 If what you say is true, I am wasting my time. But I believe there's a more diverse group of readers: 1. The people who already already know and understand what I'm explaining; 2. The people who think they know and understand what I'm explaining, but don't, and won't change their minds no matter what I write; and 3. The people who are willing to read and understand what I write, and learn from it or at least think about it. Just like medical triage, only one of the three groups can be helped, in this case #3. It's for those folks that I take the time to post. I hear from them in various ways from time to time, so I know they're out there. And I'm glad to pass along to them what I've learned, when I can. Roy Lewallen, W7EL |
transmission lines and SWR and fractional wave antennas
Art wrote:
"At the end of the radiator you state the energy is transfered to the field so I would imagine there is zero skin effect at that point and the chain of skin effect es still present on the outside of the radiator, this is because the full period has not elapsed." It will elapse as it does in every period so that the higher resistance at RF will take its toll as predicted. Because of skin effect, hollow conducting pipes exhibit almost as much conducting ability as solid rods of the same material. This creates a market for aluminum tubes as radiating elements and Copperweld wire in antennas. High-powered transmitters use silver-plated coiled pipes to carry distilled water to cool their final amplifiers. The space within the coiled pipes carries no significant RF. RF energy does not flow out on the surface of a conductor and return in the conducting material within the conductor in ordinary circumstances, although phase lag within a conductor increases as penetration depth increases. Best regards, Richard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
oh no! *now he doesn't believe in reflections! *how could we ever survive on here without endless discussions of reflections and waves? He believes that anything that trashes his delusions of how an antenna works has to be wrong. Jimmie |
transmission lines and SWR and fractional wave antennas
On Dec 29, 1:36*pm, Roy Lewallen wrote:
J. B. Wood wrote: Hello, Roy, and while the above is certainly correct, you're probably wasting your time. *Many folks like to fashion their own "reasonable" explanations even when they're completely off track (should I mention the CFA again?). *Of course they're always right and it's the rest of the world who's wrong. *Certain folks on this ng appear to be in constant need of validation. *Persons without some knowledge of the underlying physics and applied math are destined to reach the wrong conclusions IMO. *Of course that's not going to stop some from building a CFA because as we all know it's the standard comms antenna used at the Groom Lake facility to keep in touch with Klaatu. *Sincerely, and 73s from N4GGO, John Wood (Code 5550) * * * *e-mail: * * * * * * * * * * Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 If what you say is true, I am wasting my time. But I believe there's a more diverse group of readers: 1. The people who already already know and understand what I'm explaining; 2. The people who think they know and understand what I'm explaining, but don't, and won't change their minds no matter what I write; and 3. The people who are willing to read and understand what I write, and learn from it or at least think about it. Just like medical triage, only one of the three groups can be helped, in this case #3. It's for those folks that I take the time to post. I hear from them in various ways from time to time, so I know they're out there. And I'm glad to pass along to them what I've learned, when I can. Roy Lewallen, W7EL Roy, That is exactly how I felt when I declared that the addition of a radiator to a Gaussian statics field under the application of a time varying field equates to the mathematics of Maxwells laws. Nobody, including you, showed an error in that thinking. Another person provided the mathematics that proved my point again , nobody could disprove it. Anybody can view the book by Ramo and co "Fields and waves in communication Engineering" where in Appendix 11 where the a sample method of tackling the proof is available in it's entirety. Some could even read the chapter on radiastrion which spells out problems with the existing aproach. Remember when the presence of particles on a radiator is determined by any person well versed in mathematics and science then the true vehicle of communication is thus determined. All of the above is directly applicable to the stance in words only that you have expressed above but..........no action It blows my mind when people desert from mathematics and science in efforts to prevent change. T,here is no evidence what so ever that Newton's laws applicable in this case has now been discarded in science and that evidence destroys the notion of communication and the emmission of light can be attributed to a field wave form instead of the particles outlined in Gaussian law. Art |
transmission lines and SWR and fractional wave antennas
On Dec 29, 1:14*pm, Cecil Moore wrote:
Art Unwin wrote: So one acknowledges the presence of a capacitor at the end of a radiator Let's use IEEE definitions to avoid confusion. A "capacitor" is a physical component that exhibits capacitance. Capacitance can be exhibited without the existence of a physical lumped component. At the end of a radiator, we would have a distributed capacitance, not *a* lumped capacitor. No Cecil. We are at the end of the radiator and there is no eddy currents in front. Ther apparently is a gap between the outside of the radiator end which some see as a capacitor ( tho I see nothing that suggests that as yet) If one accepts a capacitor as distributed then I will go along with that but that alone cannot stop the flow of current. Regards Art And actually, it is not only at the end since it is "distributed". In fact, an antenna element can be modeled as a distributed RLC network where the R includes all "losses" including radiation. -- I would love to see that circuit in its entirety since it will show the points of collision 73, Cecil *http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
Cecil, W5DXP wrote:
"Richard , I`ll bet you know that the reflection coefficient is 1.0 for an open circuit and -1.0 for a short circuit. :-) Yes, Cecil caught me not paying attention. At an open circuit, the impedance is infinite but the coefficient of reflection is the ratio of the voltage of the reflected wave to the voltage of the incident wave. As both have the same phase and magnitude, value of the reflection coefficient for an open circuit is 1.0, not infinity. Best regards, Richard Harrison, KB5WZI |
transmission lines and SWR and fractional wave antennas
On Dec 29, 1:09*pm, (Richard Harrison)
wrote: Art wrote: "Yes, the common thinking is that current changes direction to oppose the forward moving current as with a reflection where the eddy current moving in the reverse direction cancels the eddy current moving in the other direction." Transformers are laminated to reduce eddy current core losses. Reverse currents on a transmission line or on an antenna are usually called the reflected current. Reflections are caused by discontinuities in the path of the EM wave. In the case of an open circuit, the reflection coefficient is infinite and the incident and reflected waves have the same magnitude and phase. The voltage at the discontinuity is thus doubled. See Terman`s 1955 opus page 89. But, the current goes to zero as conduction ends at the open circuit. No energy is lost in the open circuit. It is just concentrated in the electric field as the magnetic field loses its energy. Best regards, Richard Harrison, KB5WZI Richard, the above does not address my question other than a stream of words It is difficult to cull anything with respect to my question that allows for scientific debate or response to which actual numbers can be applied. I know what the status quo is with respect to present day thinking so repetitive statements provide nothing to the thread. Note how Cecil is responding in a scientific way without deviating off point and learn from it. Otherwise there is no reason for me to respond Art |
transmission lines and SWR and fractional wave antennas
On Dec 29, 2:27*pm, JIMMIE wrote:
oh no! *now he doesn't believe in reflections! *how could we ever survive on here without endless discussions of reflections and waves? He believes that anything that trashes his delusions of how an antenna works has to be wrong. Jimmie Enough of the talking Jimmie and prove the Gaussian equation transformation is wrong. You missed your chance when it was shown on the net. My earlier posting pointed you to a place so you can handle the CGS units and trash it if you can. All those posts you have wasted would not have been necessary if you had educated yourself in the mean time instead of becoming just a talking head Art |
transmission lines and SWR and fractional wave antennas
Roy Lewallen wrote:
1. The people who already already know and understand what I'm explaining; Assumes that you are omniscient and others should worship at your feet. 2. The people who think they know and understand what I'm explaining, but don't, and won't change their minds no matter what I write; Assumes that you are omniscient and anyone who disagrees with you is wrong. 3. The people who are willing to read and understand what I write, and learn from it or at least think about it. Assumes that you are omniscient and people can only learn facts from you. Roy, I don't think that any assumption of your omniscience is warranted. Is it impossible that you are wrong about anything in the world? Is the reason that you absolutely refuse to engage in a rational discussion of the role of interference in antenna systems because you might be proven to be wrong and also learn something new in the process? -- 73, Cecil http://www.w5dxp.com |
transmission lines and SWR and fractional wave antennas
On Mon, 29 Dec 2008 11:36:34 -0800, Roy Lewallen
wrote: If what you say is true, I am wasting my time. But I believe there's a more diverse group of readers: 1. The people who already already know and understand what I'm explaining; 2. The people who think they know and understand what I'm explaining, but don't, and won't change their minds no matter what I write; and 3. The people who are willing to read and understand what I write, and learn from it or at least think about it. Just like medical triage, only one of the three groups can be helped, in this case #3. It's for those folks that I take the time to post. I hear from them in various ways from time to time, so I know they're out there. And I'm glad to pass along to them what I've learned, when I can. Roy Lewallen, W7EL Well, this is probably a suitable time to offer my thanks for taking the time to explain how things work (and to correct my screwups). Thanks much. I suspect that the time and effort are not a major problem. It's tolerating the nonsense that passes as a substitute for intelligence that bothers me. It's difficult to argue with unsubstantiated illogic and one-line simulated cleverness. I do the same in alt.internet.wireless. http://groups.google.com/groups/profile?hl=en&enc_user=bLQuYRAAAACBvdjA7WBXQw3w3fq wxHRj Hmmm... there should be much more dating back to about 1987. One of my tag lines is: "I judge people by their willingness and ability to learn". I have no problem with those that disagree with me. It's easy enough to make the distinction between disagreement and learning failure. If they understand both sides of a debate, they're doing just fine. Otherwise, you're debating against dogma and bias, with little home of having anyone change their opinion. I'm mostly in #3. I read, learn, sometime ask, occasionally comment, and save some postings for reference. I'm fairly well informed in my areas of expertise, but am seriously lacking in others. Antennas is one of those where I'm lacking. Sometimes you go over my head, which is not a problem. I can dig out the details later. However, some URL's, references, and additional reading pointers would be helpful. Overall, your postings are all useful, interesting, and well worth reading. As for the diversity of the readers, it's probably all over the map. You have the difficult problem of trying to write something that is understandable by every knowledge level from complete beginner to professional antenna designer. It's easy if you know something about the person with whom your discussing some topic, but very different if you're dealing with an anonymous visitor. Thanks again. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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