|
Current through coils
Gene Fuller wrote:
As you know, generating the helix coils and using them are two separate things. I have only EZNEC version 3, which does not support automatic helix generation. However, there does not appear to be any reason why helices cannot be used in EZNEC version 3. That is what I did. I copied your wires, edited them, and re-input into EZNEC. That probably explains everything. Version 4, with the helix generation option, does a geometry check. The geometry of your coil is unacceptable to Version 4 of EZNEC. As for the height, you asked for an 8 foot whip. I adjusted my model until I got to a 10 foot whip. Actually, you stopped at 11.775 ft., ~12 feet as I stated earlier. It won't do any good to keep going. The coil you generated is unacceptable to EZNEC 4.0. But thanks for your effort. I learned something about EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote: I did what you "challenged", with the exception of the exact whip length. (And the version I sent had a total height of 11 feet 9 inches, which is not absurdly unreasonable.) I have to say I am surprised that it took you more than 24 hours to misinterpret what I sent (10 turns per foot) and then to blame the tools. I don't see any of the errors on my computer. There is little point of carrying this any further. You already stated that the results did not make technical sense to you and that perhaps EZNEC cannot be used for this task. I cannot repair your "technical sense", and I have no control over the capabilities of EZNEC. Gene, Send me the file please. Don't use my akorn newsgeroup addres. I do not check it. Use my callsign at contesting.com 73 Tom |
Current through coils
wrote:
Send me the file please. Don't use my akorn newsgeroup addres. I do not check it. Here's just about all you need to know about Gene's EZNEC file: http://www.qsl.net/w5dxp/ezerror.GIF EZNEC doesn't like 4 TPI coils at 4 MHz. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote:
"it seems that these references are not particularly concerned with dimensions of the coil with respect to wavelength, or to the mode of propagation within the coil. OK. I gave an example of a traveling wave tube which uses a coil specifically to retard wave progress ao that an electron beam could keep up with a signal winding its way through the coil.Terman describes the Traveling Wave Tube (TWT) starting on page 678 of his 1955 edition of "Electronic and Radio Engineering". Here is another version of how the TWT works. The TWT was developed to provide wideband gain, about 10 to 60 dB over 10% of the operating frequency or more, and produce a power output of one kilowatt, if needed. The TWT consists of an electron gun similar to those used in CRTs, a wire helix, and a collector. The gun at one end of the helix produces a focused beam of electrons directed through the center of the helix. The helix is a uniform coil of wire used to slow down the forward progress of an RF signal fed into the gun-end of the helix inside a glass vacuum tube. Output is taken from the helix at the collector end of the helix. The collector and the helix are positively charged. The collector is the electrode which catches the spent electrons which have traveled through the length of the tube. A magnetic field distributed along the length of the TWT is used to keep rhe electron beam from spreading during flight. Transfer of power from the direct current of the electron beam to the RF signal is by velocity modulation of the beam into periodic bunches of electrons. these accelerating electron bunches generate a stronger signal along its path. Interaction between the electron beam and the helix is continuous and accumulative. Amplitude of the signal grows as it travels down the helix. The axial wave velocity is fixed by the helix while the initial eleectron velocity (before modulation) is proportional to the positive potential on the helix and collector. The signal to be amplified is fed to the end of the helix nearer the electron gun. This RF signal travels as a surface wave around the turns of the helix, toward the collector, at about the velocity of light. The forward or axial movement of the signal is slower, of course, because of the pitch and diameter of the helix. This forward movement of the wave is analogous to the travel of a finely threaded screw where many turns are required to drive it into position. The signal wave generates an axial electric field which travels with it along the longitudinal axis of the helix. This velocity modulates (slows down and speeds up) the electrons of the beam current. So, the wave traveling from one end of the coil towards the other is a "slow-wave" while the wave travelimg around the coil turns is only slightly slowed below the speed of light. This is how a coil works. Frequency and coil form matter but don`t change the basics. Best regards, Richard Harrison, KB5WZI |
Current through coils
Cecil Moore wrote: wrote: Send me the file please. Don't use my akorn newsgeroup addres. I do not check it. Here's just about all you need to know about Gene's EZNEC file: http://www.qsl.net/w5dxp/ezerror.GIF EZNEC doesn't like 4 TPI coils at 4 MHz. -- 73, Cecil http://www.qsl.net/w5dxp Sorry Cecil, I was talking to John, and not you. I prefer low distortion accurate information that has not been run through a "Cecil Moore filter". 73 Tom |
Current through coils
Cecil,
I have no idea what you did, but you screwed something up quite royally. There is no way that segment 3 is too close to segment 197. I just ran a cut-down version in the EZNEC 4 demo, and I found no geometry errors. Yes, each segment length is too short, about 80% of the recommendation, but Roy indicated a couple of days ago that should not present a big problem. I cannot say much more about EZNEC, except that I did not see any problems. The coil I modeled is very similar to the Texas Bugcatcher model 680 coil. ( http://www.texasbugcatcher.com ) I don't own a Texas Bugcatcher coil, but I suspect they actually work more or less as advertised. 73, Gene W4SZ Cecil Moore wrote: wrote: Send me the file please. Don't use my akorn newsgeroup addres. I do not check it. Here's just about all you need to know about Gene's EZNEC file: http://www.qsl.net/w5dxp/ezerror.GIF EZNEC doesn't like 4 TPI coils at 4 MHz. |
Current through coils
On Thu, 30 Mar 2006 00:04:28 GMT, Gene Fuller
wrote: The coil I modeled is very similar to the Texas Bugcatcher model 680 coil. ( http://www.texasbugcatcher.com ) Hi Gene, Could you pass a copy my way too? 73's Richard Clark, KB7QHC |
Current through coils
Richard Clark wrote: On Thu, 30 Mar 2006 00:04:28 GMT, Gene Fuller wrote: The coil I modeled is very similar to the Texas Bugcatcher model 680 coil. ( http://www.texasbugcatcher.com ) Hi Gene, Could you pass a copy my way too? 73's Richard Clark, KB7QHC Be sure you get a copy that has not been edited in a DXP filter. Although free, the corrupted or selectively filtered data is useless. 73 Tom |
Current through coils
Cecil,
I forgot to say one thing. It appears that the files I sent you got corrupted somehow. First there was the problem of "10 turns per foot" and now all the geometry check errors. (Did you drop the card deck on the floor?) 8-) 8-) The original files are still good at my end. I will resend if that will help. 73, Gene W4SZ Cecil Moore wrote: Here's just about all you need to know about Gene's EZNEC file: http://www.qsl.net/w5dxp/ezerror.GIF EZNEC doesn't like 4 TPI coils at 4 MHz. |
Current through coils
Gene Fuller wrote:
I just ran a cut-down version in the EZNEC 4 demo, and I found no geometry errors. You only get the geometry warning after the creation of the helix, not after you store and reload the file. Create the helix and you will get those geometry warnings. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
The original files are still good at my end. I will resend if that will help. Gene, you won't understand what the problem is until you create the coil in EZNEC 4.0. Right after creation of the coil, EZNEC will display the geometry errors. After that, the geometrical errors appear to be down the list from the segment errors and unavailable for viewing. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
The original files are still good at my end. I will resend if that will help. I've been wondering why you could create close spaced coils and I couldn't without objections from EZNEC. I've been sitting here creating coils to see where the geometry check fails. On 4 MHz, with a 25 turn coil and a 0.5 ft. diameter, the turn spacing passes the geometry test at 0.175 ft. and higher but fails at 0.174 ft. and lower. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Gene Fuller wrote: The original files are still good at my end. I will resend if that will help. I've been wondering why you could create close spaced coils and I couldn't without objections from EZNEC. I've been sitting here creating coils to see where the geometry check fails. On 4 MHz, with a 25 turn coil and a 0.5 ft. diameter, the turn spacing passes the geometry test at 0.175 ft. and higher but fails at 0.174 ft. and lower. It just occurred to me that this geometry check failure that I have been seeing might be a bug in EZNEC. I just downloaded and installed the latest update and the problem seems to have been resolved. I apologize for any confusion. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote: It just occurred to me that this geometry check failure that I have been seeing might be a bug in EZNEC. I just downloaded and installed the latest update and the problem seems to have been resolved. It just took from post number 808 to post number 840, about 30 posts, to resolve an error occuring in one person's computer. For a real treat, go back to post 808 and start reading the tone of the entire exchange, and make a written list of the errors. Imagine how long it would take to resolve something complicated in this thread! Now you see why I won't get into this. I go to Waffle house when I want to look at someone turning out waffles at a high rate of speed. 73 Tom |
Current through coils
|
Current through coils
wrote:
Now you see why I won't get into this. It's not hard to see why you are afraid to comment on the graphic at: http://www.qsl.net/w5dxp/1WLDIP.GIF My statements there are either right or wrong. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
wrote: Now you see why I won't get into this. It's not hard to see why you are afraid to comment on the graphic at: http://www.qsl.net/w5dxp/1WLDIP.GIF My statements there are either right or wrong. They're just disembodied statements, Cecil. Come back when you can supplement them with some theory and experimental proof. 73, Tom Donaly, KA6RUH |
Current through coils
"Tom Donaly" wrote:
Cecil Moore wrote: It's not hard to see why you are afraid to comment on the graphic at: http://www.qsl.net/w5dxp/1WLDIP.GIF My statements there are either right or wrong. They're just disembodied statements, Cecil. Come back when you can supplement them with some theory and experimental proof. It is trivial to use EZNEC to stick a coil at those points. I have offered EZNEC proof on my web site. Nobody wants to discuss it. Wonder why? -- 73, Cecil, W5DXP |
Current through coils
"Gene Fuller" wrote: What's that old saying? Something like, "It's a poor workman who blames his tools." When I was at Intel we didn't blame our customers for Intel's programming bugs and software problems. I am happy to find out that my years-long struggles to create a decent coil in EZNEC was a program bug. Thanks to you, EZNEC is twice as useful to me today as it was yesterday. -- 73, Cecil, W5DXP |
Current through coils
"Reg Edwards" wrote: But the propagation delay, with a true transmission line, should be constant versus frequency as it depends only on coil dimensions and hence on L and C. The velocity factor should also be a constant. Reg, if the SWR on a piece of transmission line is infinite and one tries to use the standing wave current phase to measure the propagation delay in a piece of that transmission line, what would be the result? -- 73, Cecil, W5DXP |
Current through coils
Sorry Cec, but I havn't the foggiest idea what you are talking about.
---- Reg ========================================= "Cecil Moore" wrote in message . com... "Reg Edwards" wrote: But the propagation delay, with a true transmission line, should be constant versus frequency as it depends only on coil dimensions and hence on L and C. The velocity factor should also be a constant. Reg, if the SWR on a piece of transmission line is infinite and one tries to use the standing wave current phase to measure the propagation delay in a piece of that transmission line, what would be the result? -- 73, Cecil, W5DXP |
Current through coils
"Reg Edwards" wrote:
Sorry Cec, but I havn't the foggiest idea what you are talking about. Let me ask it a little differently. We all know what a plot of the standing wave current magnitude looks like up and down an open-circuit transmission line. But what does a plot of the associated standing wave current *phase* look like up and down that same open-circuited transmission line? -- 73, Cecil, W5DXP |
Current through coils
Tom, W8JI wrote:
"Many people vizualize current in a small loading inductor as starting at one end and traveling through the conductor turn-by-turn. That`s how the experts say the coul in a TWT works, and it is no different from other coils. RF energy travels in waves which induce currents on conductors in their paths which in turn induce more waves. Energy has no choice but to follow the conductor. It is nonsense to say this is not the means used by energy traveling through an inductor while riding on its surface due to skin effect. The energy follows the conductor wrapping its way around the form fron start to finish. Energy hits the speed limit of physics if it can at 300,000,000 meters per second. but its interaction with any conductor slows it depending on the characteristics of the conductor guiding it. An inductor reduces the group velocity (actual energy velocity) of any wave traveling along its surface. The group velocity is always less than the velocity of light (300,000,000 m/sec.). Phase velocity may exceed the velocity of light but only to the extent that the actual group velocity is slower than the velocity of light. An inductor reduces the group velocity of a wave traveling upn is surface.Inductors are also known as "retardation coils". The RF`s changing current generates waves. In an inductor, it ideally lags voltage across that inductor (as a circuiy element) by 90-degrees. Time represented by a 90-degree delay can be calculated by: velocity = frequency x wavelength. 90-degrees is 1/4-wavelength. It is possible to measure the delay of a circuit but when your measurement seems to violate the laws of physics it`s more likely your measurement was flawed than you have discovered any new physics. Tight coupling does not speed transfer of energy through a coil. TWT coils are tightly coupled. Remember, the coil does not allow current to change instantly. Lenz`s law prevails. Current lag enforces a delay. Tom also wrote on "Welcome to W8JI.com": "An inductor delays the flow of current in relationship to applied voltages as the magnetic field inside the coil expands. Voltage increases before current starts to flow. This phase relationship berween voltage and current is often confused with time delay in the inductor." I`m done with my critique only because I`m out of time. Best regards, Richard Harrison, KB5WZI |
Current through coils
"Cecil Moore" wrote in message . net... "Reg Edwards" wrote: Sorry Cec, but I havn't the foggiest idea what you are talking about. Let me ask it a little differently. We all know what a plot of the standing wave current magnitude looks like up and down an open-circuit transmission line. But what does a plot of the associated standing wave current *phase* look like up and down that same open-circuited transmission line? -- 73, Cecil, W5DXP ================================ What is 'phase'? --- Reg. |
Current through coils
"Reg Edwards" wrote: What is 'phase'? I'll send you a .jpg image of a page from Kraus's book. Phase is the phase of a phasor. :-) -- 73, Cecil, W5DXP .. |
Current through coils
Cecil Moore wrote:
"Reg Edwards" wrote: Sorry Cec, but I havn't the foggiest idea what you are talking about. Let me ask it a little differently. We all know what a plot of the standing wave current magnitude looks like up and down an open-circuit transmission line. But what does a plot of the associated standing wave current *phase* look like up and down that same open-circuited transmission line? -- 73, Cecil, W5DXP By now you should be able to calculate that, Cecil. 73, Tom Donaly, KA6RUH |
Current through coils
Tom Donaly wrote: Cecil Moore wrote: "Reg Edwards" wrote: Sorry Cec, but I havn't the foggiest idea what you are talking about. Let me ask it a little differently. We all know what a plot of the standing wave current magnitude looks like up and down an open-circuit transmission line. But what does a plot of the associated standing wave current *phase* look like up and down that same open-circuited transmission line? -- 73, Cecil, W5DXP By now you should be able to calculate that, Cecil. 73, Tom Donaly, KA6RUH Indeed. And I even gave the answer some time ago -- the phase of the total current (which Cecil seems to like calling the "standing wave" current) is the same all along the line. That's true only for the case of a line that's completely short or open circuited. In any other case, the phase of total voltage and current vary along the line. This can be easily calculated by adding the values of the forward and reverse traveling waves at each point to get the total at each point. Or, if you're lazy, just plug the numbers into the equations you'll find in _Reference Data for Radio Engineers_ or your favorite reference. Or if you're lazier yet you can model a transmission line with EZNEC or the modeling program of your choice and let it tell you what the phase of the current is at each point along the line. Any of the three methods will give the same result if done correctly. As I mentioned before, a plucked guitar string is a good physical analogy. Each point along the string moves in the same direction at the same time, showing that the motions at all points along the string are in phase. That's very basic transmission line theory. If Cecil really doesn't know the answer to the question he asked, it's no wonder he has such conceptual problems with inductors and transmission lines. Roy Lewallen, W7EL |
Current through coils
Richard Harrison wrote: Tom, W8JI wrote: "Many people vizualize current in a small loading inductor as starting at one end and traveling through the conductor turn-by-turn. That`s how the experts say the coul in a TWT works, and it is no different from other coils. That's not correct at all Richard. The coil in a TWT tube behaves considerably different than a small inductor operted at a low frequency. Nearly everyone on this thread seems to understand mutal coupling is very high in a conventional loading inductor. This is why the inductor comes close to following a square of the turns change in inductance. A TWT has a loose coil operated in an entitrely different mode, behaving much more like a axial mode helice than an inductor. It can easily be proven inductors don't behave the same way when they have wide turns spacing and long form factor and low values of distributed capacitive reactance to the outhside world...when compared to an inductor who's displacement current is very low compared to through current. Coils or inductors can range from having very low phase difference between each terminal (almost immeasureable) to very high values (a helical antenna or tesla coil at resonance). The only real argument against this seems to be from Cecil, and as I understood it he thinks standing waves are what causes current to be different at each end and somehow sets the phase difference between ends of the inductor. I can have a fixed style of antenna on a fixed frequency, change only the inductor design, and go from something that almost perfectly behaves like a lumped component to something that has noticable current taper across the component. Most people had this stuff right from about post one. I rarely see a thread go nowhere like this one has. It reminds me of the Fractal antenna threads years ago, or that silly conjugate match stuff that went on for years and years. 800 posts later the same major group of people seem to agree, the same one or two people seem to think something magical occurs in an antenna making a regular lumped inductor behave like a self-resonant helice with standing waves and all. It's sure a time waster. 73 Tom |
Current through coils
Roy Lewallen wrote:
Indeed. And I even gave the answer some time ago -- the phase of the total current (which Cecil seems to like calling the "standing wave" current) is the same all along the line. But Roy, you measured the phase of the standing wave current to try to convince us there was no phase shift through a loading coil. You cannot have it both ways. You cannot use the phase of the standing wave current to measure a phase shift through a loading coil and then tell us the phase of the standing wave current is the same all along the line. So which story are you going to chose? I suspect that when you made those measurements, you didn't realize that standing wave antennas have standing wave currents and that the currents reported by EZNEC for standing wave antennas are standing wave currents with unchanging phase. If the phase of the standing wave current cannot be used to measure the delay through a wire, what made you think it could be used to measure the delay through a loading coil? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
That's not correct at all Richard. The coil in a TWT tube behaves considerably different than a small inductor operted at a low frequency. A 75m bugcatcher coil is not a small inductor. You guys have backed so far out of the basic real world argument that we can't even see your coils anymore without a microscope. Of course, microscopic coils have delays that can be ignored. 75m bugcatcher coils are not microscopic. They are HUGE! How you can argue that the magnitude of the current is the same at both ends of the coil when 12 out of 13 of the measurements showed they were different is magical thinking, divorced from reality. The only real argument against this seems to be from Cecil, and as I understood it he thinks standing waves are what causes current to be different at each end and somehow sets the phase difference between ends of the inductor. If you don't understand that fact of physics, you don't understand the distributed network model at all. In a standing wave antenna, there exist forward current and reflected current. Any model that doesn't take that fact into account is doomed to failure. 800 posts later the same major group of people seem to agree, the same one or two people seem to think something magical occurs in an antenna making a regular lumped inductor behave like a self-resonant helice with standing waves and all. The magic is that current travels through coils faster than the speed of light. That's what your lumped-circuit argument presupposes. It also completely ignores reflected waves. Doesn't it seem logical to use a model that includes reflected waves when one installs a loading coil in a standing wave antenna? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
you measured
You cannot have You cannot use you going you made you didn't you think What are dreams made of? |
Current through coils
Cecil,
I guess I am a bit puzzled. The bugcatcher example I sent you showed a phase shift of about 7 degrees at 4 MHz. The current at the top of the coil drops off to about 85% of the base current. I believe the delay computes to something around 5 ns. That does not seem like a HUGE delay for a coil that contains nearly 40 feet of wire. I presume you can now duplicate and verify these results, since we have not heard any contrary information. That coil is real close in design to a genuine Texas Bugcatcher #680 from Henry Allen. Absolutely no one around RRAA clings to a rigid lumped component model, except your straw man. The distinction is that most people treat this non-ideality as a perturbation. You seem to want to elevate it to the status of realignment of the planets. It has been explained over and over why real coils are not ideal. I am sure you understand. I am not at all sure why you persist in carrying on this rather pointless argument. 73, Gene W4SZ Cecil Moore wrote: A 75m bugcatcher coil is not a small inductor. You guys have backed so far out of the basic real world argument that we can't even see your coils anymore without a microscope. Of course, microscopic coils have delays that can be ignored. 75m bugcatcher coils are not microscopic. They are HUGE! How you can argue that the magnitude of the current is the same at both ends of the coil when 12 out of 13 of the measurements showed they were different is magical thinking, divorced from reality. |
Current through coils
Gene Fuller wrote:
The bugcatcher example I sent you showed a phase shift of about 7 degrees at 4 MHz. I've been waiting for you to come back with the facts that contradict W8JI's measurements. Thanks once again. The coil has about half the inductance of the 100 uH coil measured by W8JI. He measured ~4 degrees in 100 uH. EZNEC reports 8 degrees in 60 uH for an 8.5 foot antenna. My wild ass guess was at least five times more accurate than W8JI's measurements. Thanks for pointing that out. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
I did not say anything about W8JI's measurements. He had a completely different setup, and I had nothing to do with it. You have a remarkable Teflon coating. I completely called your bluff on the bugcatcher coil, and you simply ignore the result and slide away to some other Don Quixote adventure. I am not really surprised, of course. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: The bugcatcher example I sent you showed a phase shift of about 7 degrees at 4 MHz. I've been waiting for you to come back with the facts that contradict W8JI's measurements. Thanks once again. The coil has about half the inductance of the 100 uH coil measured by W8JI. He measured ~4 degrees in 100 uH. EZNEC reports 8 degrees in 60 uH for an 8.5 foot antenna. My wild ass guess was at least five times more accurate than W8JI's measurements. Thanks for pointing that out. |
Current through coils
Richard Harrison wrote:
Tom, W8JI wrote: "Many people vizualize current in a small loading inductor as starting at one end and traveling through the conductor turn-by-turn. That`s how the experts say the coul in a TWT works, and it is no different from other coils. . . . I maintain that there's no such group as "other coils", but that coils act quite differently depending on their physical sizes and the amount of coupling between turns. I believe that current traveling down a straight wire goes at nearly the speed of light. I also believe that if you take that straight wire and wind it into a helix with very widely spaced turns, it also travels down the wire at nearly the speed of light. But if you wind a helix that's short in terms of wavelength and with a reasonable length/diameter ratio, the field from the current in each turn couples to all other turns, which makes the propagation axially from one end to the other close to the speed of light. That is, for the same length of wire, an inductor with closely coupled turns has a much lower propagation delay than one with the turns spread out in a loose helix. Do I infer from your comments that you believe that the current continues to flow along the wire at about the speed of light, so that if the wire length stays the same, the propagation delay along the widely spaced helix is the same as for the short one with close spaced turns? That is, that both these cases fall into what you categorize as "other coils", which act the same as the helix in a TWT? Roy Lewallen, W7EL |
Current through coils
Gene Fuller wrote:
Cecil, I guess I am a bit puzzled. The bugcatcher example I sent you showed a phase shift of about 7 degrees at 4 MHz. The current at the top of the coil drops off to about 85% of the base current. I believe the delay computes to something around 5 ns. That does not seem like a HUGE delay for a coil that contains nearly 40 feet of wire. I presume you can now duplicate and verify these results, since we have not heard any contrary information. That coil is real close in design to a genuine Texas Bugcatcher #680 from Henry Allen. Absolutely no one around RRAA clings to a rigid lumped component model, except your straw man. The distinction is that most people treat this non-ideality as a perturbation. You seem to want to elevate it to the status of realignment of the planets. It has been explained over and over why real coils are not ideal. I am sure you understand. I am not at all sure why you persist in carrying on this rather pointless argument. Actually Gene if you look at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm your EZNEC model's current agrees with similar coils in antennas I measured. I expect Cecil will ignore what you sent him, or announce it supports his conclusions by editing the data. 73 Tom |
Current through coils
Gene Fuller wrote:
I completely called your bluff on the bugcatcher coil, and you simply ignore the result and slide away to some other Don Quixote adventure. The EZNEC simulation is just one more data point in a large set of data points that are already widely scattered. EZNEC does not have magic or God-like properties to override reality especially when your design results in pages and pages of segmentation guideline violations. The jury is still out on the question. You guys have a habit of declaring victory when you score your first point after trailing 10-0. When only one coil out of a dozen tests showed the current at each end of the toroidal coil to be the same, W8JI declared that was proof that all coils have the same current at each end. If you will check my postings, you will see that I said the delay through a coil is what it is and we usually don't know what it is. But we do know it is NOT instantaneous and we know it is unlikely to be the 3 nS measured by W8JI. I was surprised to see EZNEC report the delay as 20% less than my lower estimate of 10 degrees. But that 8 degrees is 100% higher than W8JI's measured values. And there's your pesky posting about standing wave currents. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. If we assume the 1.013 amp at the bottom of the coil occurs when the forward and reflected currents are in phase, then the 0.7628 amps at the top of the coil would have the currents 82 degrees out of phase, i.e. a 41 degree phase shift through the coil. That is, of course, only a rough estimate, but enough different from the 8 degrees to suspect something is wrong with my suggested traveling wave antenna. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Actually Gene if you look at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm your EZNEC model's current agrees with similar coils in antennas I measured. I still don't understand how you can continue to assert that there are equal currents at each end of a loading coil when half of your own measurements show a current at the top of the coil that is 73-79% lower than the current at the bottom of the coil. And I have shown that those currents depend upon where the coil is placed in the standing wave system: http://www.qsl.net/w5dxp/current.htm http://www.qsl.net/w5dxp/1WLDIP.GIF I expect Cecil will ignore what you sent him, or announce it supports his conclusions by editing the data. Please see my posting answering Gene. The 8 degree delay value is 20% less than my lowest estimate. The 8 degree delay value for the ~70 uH coil is 100% higher than your measured value of 3 nS for a 100 uH coil. The EZNEC value is also suspicious in the face of pages and pages of segmentation violations errors reported by EZNEC. Gene Fuller wrote: The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. The phase information in a standing wave is in its amplitude and can be used to estimate the difference in phase angles between the forward and reflected currents. If the current at the top of the coil is 75% of the current at the bottom of the coil, it means that the forward and reflected current phasors are approximately 82 degrees out of phase with each other, i.e. there is roughly a 41 degree phase shift through the coil. That comes from your own measurements. The latest EZNEC results are just one more data point on a plot already containing many scattered data points. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
I maintain that there's no such group as "other coils", but that coils act quite differently depending on their physical sizes and the amount of coupling between turns. What's wrong with grouping coils that act quite differently into a set called "other coils"? But if you wind a helix that's short in terms of wavelength and with a reasonable length/diameter ratio, the field from the current in each turn couples to all other turns, which makes the propagation axially from one end to the other close to the speed of light. This is easily proven not to be true by self-resonance testing. My 75m bugcatcher is self-resonant on my GMC pickup at about 6.6 MHz. If the signal were "propagating axially from one end to the other close to the speed of light", the self-resonant frequency would be close to 1 GHz. -- 73, Cecil http://www.qsl.net/w5dxp |
| All times are GMT +1. The time now is 07:01 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com