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#1
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Gene Fuller wrote:
Cecil Moore wrote: Tom Donaly wrote: What is the characteristic impedance of Tom's coil? A few thousand ohms. Use equation 50 at: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf What's your formula for the velocity factor of Tom's coil? Is it from the same Tesla coil crackpot you quoted in previous posts? Do you reject all IEEE white papers? The formula is equation 32. Cecil, Have you actually read and understood that article? Corum mentions several times that everything he reduces to the simple formulas applies only to quarter-wave resonance conditions. Look at the author's highlight between equations 31 and 32. Look at the discussion near equation 47. Look at the discussion following equation 60. Read the entire discussion in section 5. Note that he does not say the characteristic impedance is a constant that can be deduced from resonance conditions and then applied to operating conditions. In fact, he says exactly the opposite. "It is worth noting that, for a helical anisotropic wave guide, the effective characteristic impedance is not merely a function of the geometrical configuration of the conductors (as it would be for lossless TEM coaxial cables and twin-lead transmission lines), but it is also a function of the excitation frequency." I have no comment on the validity of the Corum analysis. He makes a lot of approximations and simplifications which may or may not be completely correct. However, it is clear that you are mis-quoting him. 73, Gene W4SZ The Corum duo model their Tesla coil as "an isotropically conducting cylindrical boundary." Later, they call it a "helically disposed surface waveguide." Later, they write, "Further, the Tesla coil passes to a conventional lumped element inductor as the helix is electrically shortened." Do the first two quotes resemble a description of a typical ham antenna loading coil? Has anybody here used a Tesla coil to load an antenna? The Corums also state in one part of their paper that their method of analysis is "fraught with danger." Indeed. Cecil's misuse of the formulas certainly proves that. Many people over the years have done just fine loading their antennas with lumped inductors. There's no need to put a "helically disposed surface waveguide" on a mobile antenna, and if someone thinks that modeling a coil as "an isotropically conducting cylindrical boundary" actually turns that coil into an isotropically conducting cylindrical boundary, that someone should seek help. 73, Tom Donaly, KA6RUH |
#2
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Tom Donaly wrote:
Many people over the years have done just fine loading their antennas with lumped inductors. That's not the point of this discussion, Tom. The only question that needs to be answered here is: Can a 2" dia, 100 T, 10" long loading coil have a delay of 3 nS through it at 4 MHz? Do you support such a technical absurdity? The Corum IEEE white paper suggests that delay is in error by a magnitude. All of the boundary test conditions given in Corum's IEEE white paper are satisfied by a 75m bugcatcher loading coil. There is no reason to believe that the underlying principles of physics do not apply. In fact, the diagram of the 1/4WL resonant system looks exactly like a base loading coil, stinger, and top hat as is used for 75m mobile operation. -- 73, Cecil http://www.w5dxp.com |
#3
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Cecil Moore wrote:
Tom Donaly wrote: Many people over the years have done just fine loading their antennas with lumped inductors. That's not the point of this discussion, Tom. The only question that needs to be answered here is: Can a 2" dia, 100 T, 10" long loading coil have a delay of 3 nS through it at 4 MHz? Do you support such a technical absurdity? The Corum IEEE white paper suggests that delay is in error by a magnitude. All of the boundary test conditions given in Corum's IEEE white paper are satisfied by a 75m bugcatcher loading coil. There is no reason to believe that the underlying principles of physics do not apply. In fact, the diagram of the 1/4WL resonant system looks exactly like a base loading coil, stinger, and top hat as is used for 75m mobile operation. Do you really believe that an antenna + loading coil has to be a quarter wave long to resonate? 73, Tom Donaly, KA6RUH |
#4
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Tom Donaly wrote:
Do you really believe that an antenna + loading coil has to be a quarter wave long to resonate? Note: I am NOT talking about *physical* lengths. The phase shift from feedpoint to tip has to be *electrically 90 degrees* so the answer is yes. For a base-loaded mobile antenna, the sum of the phase shifts a PS1. The phase shift through the loading coil. PS2. The phase shift at the coil to stinger junction. PS3. The phase shift in the stinger. PS1 + PS2 + PS3 = 90 degrees. In a typical 75m base-loaded mobile antenna, PS1 may be about 40 degrees, PS2 about 40 degrees, and PS3 about 10 degrees. PS2 is a freebie lossless phase shift compliments of Mother Nature caused by the impedance discontinuity between the coil and the stinger. If that phase shift can be maximized, it should add to antenna efficiency. -- 73, Cecil http://www.w5dxp.com |
#5
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Cecil Moore wrote:
Tom Donaly wrote: Do you really believe that an antenna + loading coil has to be a quarter wave long to resonate? Note: I am NOT talking about *physical* lengths. The phase shift from feedpoint to tip has to be *electrically 90 degrees* so the answer is yes. For a base-loaded mobile antenna, the sum of the phase shifts a PS1. The phase shift through the loading coil. PS2. The phase shift at the coil to stinger junction. PS3. The phase shift in the stinger. PS1 + PS2 + PS3 = 90 degrees. In a typical 75m base-loaded mobile antenna, PS1 may be about 40 degrees, PS2 about 40 degrees, and PS3 about 10 degrees. PS2 is a freebie lossless phase shift compliments of Mother Nature caused by the impedance discontinuity between the coil and the stinger. If that phase shift can be maximized, it should add to antenna efficiency. So, since the phase shift has to be 90 degrees, the antenna should always resonate at the same frequencies a quarter wave stub of the same electrical length would resonate at, right? 73, Tom Donaly, KA6RUH |
#6
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Tom Donaly wrote:
So, since the phase shift has to be 90 degrees, the antenna should always resonate at the same frequencies a quarter wave stub of the same electrical length would resonate at, right? Not sure what you mean by this statement. 90 degrees is 90 degrees. A mobile antenna physically shorter than 1/4WL is still close to 90 degrees long at resonance. (It is not exactly 90 degrees because of the well-known end effects.) In order for the reflected wave to be in phase with the forward wave at the feedpoint (purely resistive feedpoint impedance), the reflected wave must traverse 180 *electrical degrees* during its round trip. That fact inticates that the antenna is electrically 90 degrees long. -- 73, Cecil http://www.w5dxp.com |
#7
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"Cecil Moore" wrote
All of the boundary test conditions given in Corum's IEEE white paper are satisfied by a 75m bugcatcher loading coil. There is no reason to believe that the underlying principles of physics do not apply. In fact, the diagram of the 1/4WL resonant system looks exactly like a base loading coil, stinger, and top hat as is used for 75m mobile operation. _____________ Cecil, Do you believe that a 75m mobile antenna system using an artificially resonant (as in bugcatcher-loaded), electrically short whip produces the same elevation pattern and groundwave field strength at 1 km as an unloaded 1/4-wave vertical monopole for 75m with the same applied power using a good, buried radial r-f ground (say, 2 ohms or less)? RF |
#8
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Richard Fry wrote:
Do you believe that a 75m mobile antenna system using an artificially resonant (as in bugcatcher-loaded), electrically short whip produces the same elevation pattern and groundwave field strength at 1 km as an unloaded 1/4-wave vertical monopole for 75m with the same applied power using a good, buried radial r-f ground (say, 2 ohms or less)? No, the radiation pattern depends upon the *physical* length. The feedpoint impedance depends upon the *electrical* length. (I haven't said anything about the radiation pattern in my postings.) Unless the antenna is "full-sized", the physical length and electrical length are different. There is a free lossless phase shift between the top of a loading coil and the stinger. There's obviously zero radiation from that dimensionless point. That 40 electrical degrees of antenna is not physically there so it cannot radiate. -- 73, Cecil http://www.w5dxp.com |
#9
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On 29 Nov, 09:42, "Tom Donaly" wrote:
Gene Fuller wrote: Cecil Moore wrote: Tom Donaly wrote: What is the characteristic impedance of Tom's coil? A few thousand ohms. Use equation 50 at: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf What's your formula for the velocity factor of Tom's coil? Is it from the same Tesla coil crackpot you quoted in previous posts? Do you reject all IEEE white papers? The formula is equation 32. Cecil, Have you actually read and understood that article? Corum mentions several times that everything he reduces to the simple formulas applies only to quarter-wave resonance conditions. Look at the author's highlight between equations 31 and 32. Look at the discussion near equation 47. Look at the discussion following equation 60. Read the entire discussion in section 5. Note that he does not say the characteristic impedance is a constant that can be deduced from resonance conditions and then applied to operating conditions. In fact, he says exactly the opposite. "It is worth noting that, for a helical anisotropic wave guide, the effective characteristic impedance is not merely a function of the geometrical configuration of the conductors (as it would be for lossless TEM coaxial cables and twin-lead transmission lines), but it is also a function of the excitation frequency." I have no comment on the validity of the Corum analysis. He makes a lot of approximations and simplifications which may or may not be completely correct. However, it is clear that you are mis-quoting him. 73, Gene W4SZ The Corum duo model their Tesla coil as "an isotropically conducting cylindrical boundary." Later, they call it a "helically disposed surface waveguide." Later, they write, "Further, the Tesla coil passes to a conventional lumped element inductor as the helix is electrically shortened." Do the first two quotes resemble a description of a typical ham antenna loading coil? Has anybody here used a Tesla coil to load an antenna? The Corums also state in one part of their paper that their method of analysis is "fraught with danger." Indeed. Cecil's misuse of the formulas certainly proves that. Many people over the years have done just fine loading their antennas with lumped inductors. There's no need to put a "helically disposed surface waveguide" on a mobile antenna, and if someone thinks that modeling a coil as "an isotropically conducting cylindrical boundary" actually turns that coil into an isotropically conducting cylindrical boundary, that someone should seek help. 73, Tom Donaly, KA6RUH- Hide quoted text - - Show quoted text - Tom, May I point out that a Tesla coil is an "antenna" that does not conform to Maxwells laws with respect to the adherance to the LC ratio. The LC ratio is out of balance such that the capacitor is not of the correct size to store and then return the imposed energy from the inductive heavy coil which is visually seen as resulting in a spark. Regards Art |
#10
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![]() Tom, May I point out that a Tesla coil is an "antenna" that does not conform to Maxwells laws with respect to the adherance to the LC ratio. The LC ratio is out of balance such that the capacitor is not of the correct size to store and then return the imposed energy from the inductive heavy coil which is visually seen as resulting in a spark. Regards Art Huh... tesla coils follow all of Maxwells equations quite nicely. Paul Nicholson did some very nice analysis on this a few years back, published at a link previously posted. They're two coupled LC resonant circuits, with the coupling adjusted to around k=0.2. There are higher order systems with 3 or more resonators, as well (called Magnifiers in the TC world) The challenge in spark making is choosing appropriate operating parameters (coupling, radius of curvature, topload capacitance, etc.) to optimally promote spark growth. |
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