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Loading Coils; was : Vincent antenna
On Wed, 05 Dec 2007 15:43:11 GMT, Cecil Moore
wrote: Toroidal current pickup coils designed by W7EL with the standard voltage probes. What did you load those pickup coils with? Do you have an URL to the design? |
Loading Coils; was : Vincent antenna
"art" wrote
"The resultant vector of all vectors involved with radiation" is ONE vector. If it "can NEVER be at right angles to the axis of a radiator" then how can a monopole have any radiation in such directions? RF I have had it with you and your senior moments and misquotes. I asked you to stop so you had fair warning PLONK. Enough is enough Art Unwin KB9MZ....xg (uk) ________________ Art may have plonked me, but if so it was because I DID understand what he wrote -- not that I didn't. But at least now he won't have to respond to this reality. RF |
Loading Coils; was : Vincent antenna
On 5 Dec, 10:39, (Richard Harrison) wrote:
Art wrote: The resultant vector of all vectors involved with radiation can NEVER be at right angles to the axis of the radiator. PERIOD." A radial mode helix can and does work, despite Art`s apparent disputation. The radial mode helix acts as a stacked horizontal loop antenna. Hams routinely use horizontal loops for more bandwidth with less drivepoint resistance variation in a centerfed half wavelength of wire. When the length of wire goes from 0,5 WL to 0.6 WL the dipole increases its resistance from 70 ohms to 140 ohms. The loop feedpoint increases from 5 ohms to 7 ohms (theat`s less than a double as in the dipole. This information is found in Figs 7-19 and 8-14 of Bailey`s "TV and Other Receiving Antennas". Best regards, Richard Harrison, KB5WZI Richard, look again at the phrase "resultant vector" which means it is one vector. This angle is reflected by the "Pitch" in a helical antenna. All the other words are unnessesary and non relavent with respect to RESULTANT VECTOR. Art |
Loading Coils; was : Vincent antenna
Gene Fuller wrote:
. . . * EZNEC does not know or care about "standing waves" and "traveling waves". As has been explained many times, the NEC-based simulation tools simply look at the total current, without making any philosophical value judgments about the mobility of the waves. It is clear that you have loaded some sort of conditions into EZNEC that you believe represent standing waves and traveling waves. However, the argument becomes completely circular at that point, as you have loaded the conditions that give exactly the results you desire. If there is a hidden "wave type" parameter in EZNEC, please let us know. I will humbly retract my criticism. . . . You are of course completely right, and I've explained this to Cecil several times. But he seems to have difficulty with the concept of current as being simply the rate of charge flow. EZNEC does not, either in internal calculations or in reporting, split the current into any kind of "traveling wave", "standing wave", or any other kind of wave components. Anyone interested in the details of EZNEC calculations can find them in the NEC-2 manual which is available on line. Roy Lewallen, W7EL |
Loading Coils; was : Vincent antenna
On 5 Dec, 10:51, (Richard Harrison) wrote:
Art wrote: "The resultant vector of all vectors involved with radiation can NEVER be at right angles to the axis of the radiator. PERIOD." I`ve already defended the radial mode helix, but think of almost any simple antenna. Doesn`t the half-wave dipole dradiate principally at right angles to its axis? Best regards, Richard Harrison, KB5WZI It doesw radiate at right angles of the axis but for maximumum radiation of a particular TYPE then the resultant maximum radiation vector is between ten and fifteen degrees from the ninety angle. The total radiation is the same at right angles as to that when tilted 10 degrees or more from that angle. If you play with the angles on any computor program including EZNEC I suppose, using a wavelength radiator, this is readily seen Remember, do not stray from the term "RESULTANT VECTOR" which is the subject of discussion.End of discussion Art Art |
Loading Coils; was : Vincent antenna
On Wed, 5 Dec 2007 12:18:17 -0800 (PST), art
wrote: do not stray from the term "RESULTANT VECTOR" It might help to know the vector units; it might help to know result of what vector operation. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
"art" wrote
It doesw radiate at right angles of the axis but for maximumum radiation of a particular TYPE then the resultant maximum radiation vector is between ten and fifteen degrees from the ninety angle. The total radiation is the same at right angles as to that when tilted 10 degrees or more from that angle. If you play with the angles on any computor program including EZNEC I suppose, using a wavelength radiator, this is readily seen ______________ Below is table of free-space field values for the radiation of a vertical, full-wave, center-fed dipole, from the horizontal plane to +/- 60 degrees of elevation, using the "resultant maximum radiation vector." Note that an elevation angle of zero degrees is at right angles to this radiator. Please explain how this validates the theory stated in your quote above. RF EZNEC Demo ver. 4.0 Art's Tilt Theory of Radiation 12/5/2007 2:56:18 PM --------------- FAR FIELD PATTERN DATA --------------- Frequency = 1 MHz Field in mV/m for 1 kW at 1 km Elevation Pattern Azimuth angle = 0 deg. Deg V Fld 0 - 270.51 5 - 266.37 10 - 254.31 15 - 235.32 20 - 210.94 25 - 182.99 30 - 153.43 35 - 124.07 40 - 96.47 45 - 71.82 50 - 50.87 55 - 34.00 60 - 21.24 |
Loading Coils; was : Vincent antenna
On 5 Dec, 12:35, Richard Clark wrote:
On Wed, 5 Dec 2007 12:18:17 -0800 (PST), art wrote: do not stray from the term "RESULTANT VECTOR" It might help to know the vector units; it might help to know result of what vector operation. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On 5 Dec, 12:35, Richard Clark wrote:
On Wed, 5 Dec 2007 12:18:17 -0800 (PST), art wrote: do not stray from the term "RESULTANT VECTOR" It might help to know the vector units; it might help to know result of what vector operation. 73's Richard Clark, KB7QHC Richard You surely know that there are magnetic vectors, electric vectors and ofcourse curl. You don't need to know the vector units to see that the resultant vector cannot be on the same axis as the radiator! Ofcourse the total amount of radiation does not change with tipping the radiator a few degrees, but what type of radiation with respect to polarisation that make up total radiation surely DOES. Now Terman did not mention that as he surely would have if it were true! Hoping you do not have a relapse with respect to my postings Regards Art Unwin KB9MZ |
Loading Coils; was : Vincent antenna
On Wed, 5 Dec 2007 13:51:57 -0800 (PST), art
wrote: You surely know that there are magnetic vectors, electric vectors and ofcourse curl. You don't need to know the vector units to see that the resultant vector cannot be on the same axis as the radiator! Still and all, what is the unit for the Resultant Vector? What operation did you perform that it is the result of? 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
Richard Fry wrote:
"Field in mV/m for 1 kW at 1 km Elevation pattern----" Richard`s field strengths are consistent with Terman`s formula for field strength on page 864 of his 1955 opus, equation (23-1): E = 60pi/d (length/lambda) I cos theta (cos omega) (t-d/c) Theta is the vertical elevation angle and, of course, at zero degrees (the horizontal) cos theta =1, and at 90 degrees, cos theta = zero. This gives the field strength from an elementary vertical doublet as diagrammed on the next page. Omega is the angular frequency. I is the uniform current through the element. Terman says: "The laws governing such radiation are obtained by using Maxwell`s equations to express the fields associated with the wire; when this is done there is found to be a component, termed the radiated field, having a strength rhat varies inversely with distance." The 1/4-wave vertical along with its image in a perfect ground is shown on page 887 to have the same elevation pattern. Best regards, Richard Harrison, KB5WZI |
Loading Coils; was : Vincent antenna
On 5 Dec, 12:35, Richard Clark wrote:
On Wed, 5 Dec 2007 12:18:17 -0800 (PST), art wrote: do not stray from the term "RESULTANT VECTOR" It might help to know the vector units; it might help to know result of what vector operation. 73's Richard Clark, KB7QHC Richard, You are obviously behind in physics with this succession of questions like a prosecutor adressing the accused. You start off with a vector along the axis of the radiator and by adding a couple more vectors which you feel is in order with the circumstaces and you come up with the resultant vector. Can you think of a appropiate situation where the resultant follows the same direction of the initial starting vector? One of the remaining vectors is at right angles to the axis and the other vector represents "curl" Regards Art |
Loading Coils; was : Vincent antenna
On 5 Dec, 14:56, (Richard Harrison) wrote:
Richard Fry wrote: "Field in mV/m for 1 kW at 1 km Elevation pattern----" Richard`s field strengths are consistent with Terman`s formula for field strength on page 864 of his 1955 opus, equation (23-1): E = 60pi/d (length/lambda) I cos theta (cos omega) (t-d/c) Theta is the vertical elevation angle and, of course, at zero degrees (the horizontal) cos theta =1, and at 90 degrees, cos theta = zero. This gives the field strength from an elementary vertical doublet as diagrammed on the next page. Omega is the angular frequency. I is the uniform current through the element. Terman says: "The laws governing such radiation are obtained by using Maxwell`s equations to express the fields associated with the wire; when this is done there is found to be a component, termed the radiated field, having a strength rhat varies inversely with distance." The 1/4-wave vertical along with its image in a perfect ground is shown on page 887 to have the same elevation pattern. Best regards, Richard Harrison, KB5WZI Richard, For goodness sake read the operative word of this side thread. It is RESULTANT VECTORreferring to the summation of all vectors of a radiator. Every thing you are saying has no relavence to this term what so ever. Prove to the world yourself that maximum horizontal polarised radiation occurs when the radiator is parallel to the earths surface and be done with it. You surely are aware of antenna computor programs, use them or enquire. You are surely aware that physics have moved on in the last fifty years and you can't bury yourself or bring the past into the present because of your reluctance to change because of your work years experiences. You have a antenna computor program expert in this group whose program which is based on Maxwellian laws confirm that for maximum horizontal polarization the radiator is tipped away from the earth's surface with respect to parallism. These are not my laws, they are Maxwells. It is not my program design, it is Roy's. If you want to disagree with his programs findings take it up with him, (he stands by on this newsgroup solely to support EZNEC and welcomes questions) or any author of NEC2,NEC4 or mininec computor programs, all of which show the same results. Put away your Terman bible which represents the past and address the subject at hand today and throw away your resume of the past. Remember the subject key word " resultant vector" It is clear, it means what it says. It is not open to substitutions like substituting total gain for total horizontally polarized gain. Why O why do participants such as yourself want to elongate all threads by imposing deliberate deviations that reflect the decline of an aged brain and respective reading skills Regards Art Art |
Loading Coils; was : Vincent antenna
Richard Fry wrote:
The fact that adding a coil to an 11-degree radiator produced the system reactance a 90-degree, unloaded, linear radiator does not mean that the coil and its junction to the stinger have supplied the "missing electrical degrees" to the antenna system. The RADIATOR is still only 11 degrees long, and will have same radiation resistance and relative field pattern, regardless of the coil. The coil only supplied a non-reactive condition at the system feedpoint. I don't know how many times I've said this discussion about current distribution in a loading coil doesn't have anything at all to do with the radiation pattern. The effort spent here in bitter argument about phase shift through a coil, and missing degrees would be better spent on methods of improving the radiation resistance of such systems, and reducing the matching and r-f ground losses that limit their performance. That may well be true. Please feel to start a thread with that subject matter. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Richard Harrison wrote:
Cecil, W5DXP wrote: "However, the side that believes that a coil replaces all of the missing antenna degrees is wrong." It certainly can! It radiated very well without any stinger or mast. My statement assumed a stinger attached to the coil. Of course, at the self-resonant frequency a coil is 100% antenna and vice versa. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Yuri Blanarovich wrote:
Glad that W8JI does not wear inquisitor mantle, or you would have fried by now Cecil :-) Does it make you want to storm his Bastille? :-) -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Art wrote:
"These are not my laws, they are Maxwell`s" Yes. They are old butthey still work. Art`s discovery of Gaus has not replaced Maxwell`s equations. The origin of Maxwell`s equations may be of interest. Faraday found that voltage induced in a loop is directly proportional to the rate of change of the magnetic flux which passes through a loop. Voltage arises more or less all along the contour of the loop. Faraday`s law is: V = -dphi/dt Flux passing through the contour is the integral of the flux density. The rate of change of the total flux is thus the tate of change of the integral. In the years 1856-1873, Maxwell rewrote Faraday`s law by substiturions to equate the electric field with the changing magnetic flux. The contour of the magnetic field does not require a current carrying wire around it. An electric field is present in space so long as a changing magnetic field is present. Another discovery was that the magnetomotive force around a current is 4 pi I. It does not depend on shape or distance in the contour. Displacement flux is created in a dielectric whenever an electric field is applied. Electric charges can create it, so it is expressed in coulombs per square meter. Displacement current is proportional to the rate of change of the dielectric displacement. Maxwell knew about displacement current and speculated it would poduce magnetic flux the same as conduction current does. That was the key to electromagnetic radiation. If an alternating current flows in a wire, an alternating magnetic field will be produced in the space around the wire. The alternating magnetic field creates an alternating electric field in the surrounding space. This alternating electric field creates an alternating displacement "current" in the dielectric (maybe it should be called a displacement stress since the dielectric is an insulator) of space which gives rise to another alternating magnetic field. This expanding succession of fields continues ad infinitum. Heinrich Hertz proved in 1888 that Mexwell`s speculations were correct. The preceding is presented much more elegantly by B. Whitfield Griffith, Jr. in "Radio-Electronic Transmission Fundamentals" from which it was lifted. |
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Gene Fuller wrote:
* EZNEC does not know or care about "standing waves" and "traveling waves". Exactly!!! That's why it is a good tool for such. EZNEC is not biased. EZNEC reports standing-wave current when only it exists. EZNEC reports traveling-wave current when only it exists. Phase needs to be carefully defined for the case at hand. In this case, phase is defined by EZNEC. It is the phase of the total current referenced to the reference phase of the source. In summary, if this page is intended to resolve any serious debate, it does not. This stuff is already fully understood by everyone in the debate. Of course, you knew all of this all the time and there's nothing new here. That's why we have been arguing for three years about it. :-) -- 73, Cecil http://www.w5dxp.com |
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Gene Fuller wrote:
Cecil Moore wrote: Unfortunately, it is rumored that W8JI has talked ON4UN into changing that in the latest edition. I emailed ON4UN about it but got no reply. It has been changed. There is no longer any discussion of "degrees", only "current". It is too bad that W8JI has that much political power. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
On Wed, 05 Dec 2007 15:43:11 GMT, Cecil Moore wrote: Richard Clark wrote: Using what probes? Toroidal current pickup coils designed by W7EL with the standard voltage probes. What size 600 ohm non-inductive resistors? 50 watt devices removed from a military surplus antenna tuner. I have a number of these devices if anyone needs them. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
On Wed, 05 Dec 2007 15:43:11 GMT, Cecil Moore wrote: Toroidal current pickup coils designed by W7EL with the standard voltage probes. What did you load those pickup coils with? Do you have an URL to the design? It was in an article by Roy, W7EL, but I can't lay my hands on it at the moment. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Roy Lewallen wrote:
EZNEC does not, either in internal calculations or in reporting, split the current into any kind of "traveling wave", "standing wave", or any other kind of wave components. Sorry, you are wrong, Roy. EZNEC faithfully reports traveling wave current when reflected wave current is not present. If you had looked at the file I sent to you instead of threatening to refund my money, you would know that. Model a rhombic antenna. EZNEC reports the traveling wave amplitude and phase. Model a lossless stub. EZNEC reports the standing wave amplitude and phase. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On 5 Dec, 19:26, (Richard Harrison) wrote:
Art wrote: "These are not my laws, they are Maxwell`s" Yes. They are old butthey still work. Art`s discovery of Gaus has not replaced Maxwell`s equations. The origin of Maxwell`s equations may be of interest. Faraday found that voltage induced in a loop is directly proportional to the rate of change of the magnetic flux which passes through a loop. Voltage arises more or less all along the contour of the loop. Faraday`s law is: V = -dphi/dt Flux passing through the contour is the integral of the flux density. The rate of change of the total flux is thus the tate of change of the integral. In the years 1856-1873, Maxwell rewrote Faraday`s law by substiturions to equate the electric field with the changing magnetic flux. The contour of the magnetic field does not require a current carrying wire around it. An electric field is present in space so long as a changing magnetic field is present. Another discovery was that the magnetomotive force around a current is 4 pi I. It does not depend on shape or distance in the contour. Displacement flux is created in a dielectric whenever an electric field is applied. Electric charges can create it, so it is expressed in coulombs per square meter. Displacement current is proportional to the rate of change of the dielectric displacement. Maxwell knew about displacement current and speculated it would poduce magnetic flux the same as conduction current does. That was the key to electromagnetic radiation. If an alternating current flows in a wire, an alternating magnetic field will be produced in the space around the wire. The alternating magnetic field creates an alternating electric field in the surrounding space. This alternating electric field creates an alternating displacement "current" in the dielectric (maybe it should be called a displacement stress since the dielectric is an insulator) of space which gives rise to another alternating magnetic field. This expanding succession of fields continues ad infinitum. Heinrich Hertz proved in 1888 that Mexwell`s speculations were correct. The preceding is presented much more elegantly by B. Whitfield Griffith, Jr. in "Radio-Electronic Transmission Fundamentals" from which it was lifted. Now you are being silly Richard.Try reading what the discussion is about before you pick up a book to quote. Maxwells laws are NOT in contention. I have no idea where you got that from, maybe another thread. What we are talking about is the trail from Newton to Maxwellian laws which will allow for a full understanding. We have the laws which we all can agree on but the present trail has a lot of gaps. Why do you think that Einstein and many others spent so much time trying to fill in the gaps especially with respect to particles? Or was it in a book that was held from distribution? Richard hold off for 24 hours before you post, you mind is not as agile as it once was. Art |
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AI4QJ wrote:
Going further, I am still trying to consider how the extra angle can also be absorbed "into" an impedance discontinuity. I have started a phasor diagram of it but it is not finished yet. Maybe a Smith Chart explanation will work. All lines are lossless. On a Smith Chart normalized to 100 ohms, lay out the 10 degrees of 100 ohm line from the infinity point, i.e. the open-circuit point. The reactance value is tan(90-10) = 5.67. That means the reactance value is 5.67*100 = -j567 ohms which has to be the value at the impedance discontinuity. Now on a Smith Chart normalized to 600 ohms, lay out the x degrees of 600 ohm line from the zero point to the point where -j567/600 is located. Read the number of degrees required. It is Arctan(567/600) which is equal to ~43 degrees. The phase shift at the impedance discontinuity is therefore 90-10-43 = 37 degrees. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Wed, 5 Dec 2007 16:21:39 -0800 (PST), art
wrote: On 5 Dec, 12:35, Richard Clark wrote: On Wed, 5 Dec 2007 12:18:17 -0800 (PST), art wrote: do not stray from the term "RESULTANT VECTOR" It might help to know the vector units; it might help to know result of what vector operation. 73's Richard Clark, KB7QHC Richard, You are obviously behind in physics with this succession of questions like a prosecutor adressing the accused. You start off with a vector along the axis What is the vector's unit? 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Wed, 05 Dec 2007 22:02:50 -0600, Cecil Moore
wrote: Richard Clark wrote: On Wed, 05 Dec 2007 15:43:11 GMT, Cecil Moore wrote: Toroidal current pickup coils designed by W7EL with the standard voltage probes. What did you load those pickup coils with? Do you have an URL to the design? It was in an article by Roy, W7EL, but I can't lay my hands on it at the moment. What did you load those pickup coils with? |
Loading Coils; was : Vincent antenna
On Wed, 05 Dec 2007 15:43:11 GMT, Cecil Moore
wrote: Richard Clark wrote: Using what probes? Toroidal current pickup coils designed by W7EL with the standard voltage probes. What voltages did they present to the O'scope? |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
AI4QJ wrote: Going further, I am still trying to consider how the extra angle can also be absorbed "into" an impedance discontinuity. I have started a phasor diagram of it but it is not finished yet. Maybe a Smith Chart explanation will work. All lines are lossless. On a Smith Chart normalized to 100 ohms, lay out the 10 degrees of 100 ohm line from the infinity point, i.e. the open-circuit point. The reactance value is tan(90-10) = 5.67. That means the reactance value is 5.67*100 = -j567 ohms which has to be the value at the impedance discontinuity. Now on a Smith Chart normalized to 600 ohms, lay out the x degrees of 600 ohm line from the zero point to the point where -j567/600 is located. Read the number of degrees required. It is Arctan(567/600) which is equal to ~43 degrees. The phase shift at the impedance discontinuity is therefore 90-10-43 = 37 degrees. Wrong. In the first place, you obviously don't know the criterion for resonance. In the second place you just assume the number 90 without any reason. In the third place, the number 37 has only your assumption for the necessity of a 90 degree phase shift to justify its existence. As I wrote before, this is pretty poor shooting for a professional symbol slinger. 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
What did you load those pickup coils with? Sorry, I don't remember. I just copied what W7EL suggested. It may have been a 50 ohm carbon resistor at the end of a length of 50 ohm coax. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Dec 5, 8:47 pm, "AI4QJ" wrote:
And I was making a big mistake considering it as a lumped component (like the 1950's concept) until I was brought up to date here so I should not badmouth ARRL. That photo using a thermocouple type ammeter on both ends of the coil, where they even turned the coil upside down and repeated the measurement was pretty convincing although there is enough controversy by the people in this ng that it needs to be verified more. Going further, I am still trying to consider how the extra angle can also be absorbed "into" an impedance discontinuity. You are saying that 44 degrees phase shift is equal to 44 degrees electrical length? Thus, using "phase shift", provided (resistance free) by nature, it is possible to have electrical length over zero physical length? I still have some considering to do on that one but it is immensly interesting to say the least. In your deliberations, do consider the case where the impedance matching is obtained using lumped components. All of the "phase shift" will then be occurring over 0 length. I am reminded of the small joke: Three people need to rent a room for the night. The each give the clerk $10 for a total of $30. The clerk realizes the price is $25 and gives the valet 5 one dollar bills to refund to the people. But it is hard to split $5 three ways, so they each take $1 and tip the valet $2. So 3 people each paid $9 and the valet got $2 for a total of $29. But the original was $30. Where did the extra $1 go? Perhaps there is just no reason why the "phase shifts" should add to 90. That would make the problem go away. ....Keith |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
What voltages did they present to the O'scope? Sorry, I don't remember and can't find my lab notebook at the moment. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Tom Donaly wrote:
Wrong. In the first place, you obviously don't know the criterion for resonance. In the second place you just assume the number 90 without any reason. In the third place, the number 37 has only your assumption for the necessity of a 90 degree phase shift to justify its existence. As I wrote before, this is pretty poor shooting for a professional symbol slinger. Tom, you obviously don't know what you are talking about or how to do the analysis and are now just waving your hands in emotional frustration. The criterion for resonance is a 90 degree phase shift end-to-end in the stub. MicroSmith and antenna analyzer measurements verify the shortened stub is resonant at the design frequency with the 100 ohm section of 10 degrees and the 600 ohm section a tad longer than 43 degrees. I have been designing these shortened dual-Z0 stubs for at least 20 years. The larger question is: Why don't you know how to verify or disprove my figures? Is this subject beyond your engineering comprehension level? -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Keith Dysart wrote:
Perhaps there is just no reason why the "phase shifts" should add to 90. That would make the problem go away. But there is every reason why the phase shifts *must* add up to 90 degrees (or 270 or 450 or ...). The only way you can get zero ohms looking into an open stub is if the phase shift end-to-end is 90 degrees (or 270 or 450 or ...). The reflected current must arrive back at the feedpoint in phase with the forward current for the stub to be 1/4WL resonant. In a typical loaded mobile antenna, the only way to get a resistive feedpoint impedance is if the antenna is electrically 90 degrees long. Take a 1/4WL straight monopole wire. It is electrically 90 degrees long. Put one turn of loading in it. Is it still electrically 90 degrees long or not? Proceed until the antenna is all coil, i.e. self-resonant. Is it still electrically 90 degrees long or not? -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Dec 6, 8:59 am, Cecil Moore wrote:
Keith Dysart wrote: Perhaps there is just no reason why the "phase shifts" should add to 90. That would make the problem go away. But there is every reason why the phase shifts *must* add up to 90 degrees (or 270 or 450 or ...). The only way you can get zero ohms looking into an open stub is if the phase shift end-to-end is 90 degrees (or 270 or 450 or ...). The reflected current must arrive back at the feedpoint in phase with the forward current for the stub to be 1/4WL resonant. In a typical loaded mobile antenna, the only way to get a resistive feedpoint impedance is if the antenna is electrically 90 degrees long. Take a 1/4WL straight monopole wire. It is electrically 90 degrees long. Put one turn of loading in it. Is it still electrically 90 degrees long or not? Proceed until the antenna is all coil, i.e. self-resonant. Is it still electrically 90 degrees long or not? You are good at building scenarios that align with your hypotheseses. To test your hypothesis for correctness you need to examine the scenarios that may not align rather than those that do. And you already have one. You have needed to invent a phase shift occuring at an impedance discontinuity to explain the missing "electrical length". You should also consider a shortened monopole where lumped elements are used to tune out the reactance. Also consider a lengthened monople where either distributed or lumped elements are used to tune it. You should consider a pure lumped element circuit that presents the same impedance. Identify the locations that sum to a 90 degree "electrical length". Lastly, for real fun, find the 90 degree "electrical length" in a crystal. ....Keith |
Loading Coils; was : Vincent antenna
On Thu, 06 Dec 2007 13:00:06 GMT, Cecil Moore
wrote: Richard Clark wrote: What voltages did they present to the O'scope? Sorry, I don't remember and can't find my lab notebook at the moment. What was used as the phase reference? |
Loading Coils; was : Vincent antenna
On Thu, 06 Dec 2007 13:00:06 GMT, Cecil Moore
wrote: Richard Clark wrote: What voltages did they present to the O'scope? Sorry, I don't remember and can't find my lab notebook at the moment. How much power was applied to the network? |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Keith Dysart wrote: Perhaps there is just no reason why the "phase shifts" should add to 90. That would make the problem go away. But there is every reason why the phase shifts *must* add up to 90 degrees (or 270 or 450 or ...). That's true only if you assume the desired feedpoint impedance must be the lowest possible value. And I think, as you have pointed out on more than one occasion, the current maximum is not usually located at the feedpoint, where it would otherwise be if the current minimum is located 90 degrees away. 73 jk |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Tom Donaly wrote: Wrong. In the first place, you obviously don't know the criterion for resonance. In the second place you just assume the number 90 without any reason. In the third place, the number 37 has only your assumption for the necessity of a 90 degree phase shift to justify its existence. As I wrote before, this is pretty poor shooting for a professional symbol slinger. Tom, you obviously don't know what you are talking about or how to do the analysis and are now just waving your hands in emotional frustration. The criterion for resonance is a 90 degree phase shift end-to-end in the stub. MicroSmith and antenna analyzer measurements verify the shortened stub is resonant at the design frequency with the 100 ohm section of 10 degrees and the 600 ohm section a tad longer than 43 degrees. I have been designing these shortened dual-Z0 stubs for at least 20 years. The larger question is: Why don't you know how to verify or disprove my figures? Is this subject beyond your engineering comprehension level? I'm not an engineer, so I don't have an engineering comprehension level. Secondly, you must have figured this out with the aid of a Smith chart or you'd know exactly how many degrees you need for your 600 ohm line. Finally, if you don't know how to prove your own figures, how do you expect me to be able to do it? Do you know how to figure the other zeros in this line? Are they the same as they would be in a quarter wave line with identical Zo's? 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
Keith Dysart wrote:
You should also consider a shortened monopole where lumped elements are used to tune out the reactance. Please feel free to pursue that line of development if you are so inclined. Since lumped elements do not exist in reality, they are outside of the scope of real-world 75m mobile loading coils that I am trying to cover here. I am not proposing a theory of everything nor do I intend to waste my time with such. But be my guest. The ARRL Antenna Book equations for a small loop are "wrong" for a large loop. Moral: Recognize the limitations of the model being used. Lastly, for real fun, find the 90 degree "electrical length" in a crystal. Even Einstein's theory of relativity has its limitations. It is a diversion to try to require every model to cover every real and imagined possibility. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
What was used as the phase reference? Channel 1 was used for the phase reference for Channel 2. The time-phase difference between the two signals at zero-crossing was the the delay through the coil measured using traveling-wave current. -- 73, Cecil http://www.w5dxp.com |
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