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#271
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And so your prediction is. . . ?
Roy Lewallen, W7EL Richard Harrison wrote: Roy, W7EL wrote: "And, Richard (Harrison), who said something like "an inductor without phase shift is like"...I don`t recall ; hot dog without ketchup or something." My analogy may not have been apt, but fact is that you don`t have an inductor without phase shift. The current lags the voltage in an inductor. My dictionary says that phase is a particular stage or point of adbvancement in a cycle; the fractional part of the period through which the time has advanced, measured from some arbitrary origin. Apply a voltage or the voltage across the inductance. Current does not change instantaneously in an inductance, but it lags the imposed voltage change. Lag is to move slowly or fall behind. In a circuit containing resistance and inductance, almost all real world circuits, current lags the voltage. This is phase shift by definition. We correct power factor to overcome phase lag and to eliminate the excess current and loss from the inductive charging and discharging current of an inductive circuit. Reactance only stores energy and does no useful work. I reiterate the accuracy of my postings in this thread, and indeed, inductance and phase shift are inseparable. Please note that inductance can be neutralized with capacitance. Best regards, Richard Harrison, KB5WZI |
#272
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Can I conclude from this that if I were to make a coil with more or less
inductance, then I would see a current difference between the ends of the coil? So tell you what. If you'll pull out your equations and calculate the expected current difference, I'll replace the coil with one of 100 ohms reactance and remeasure. How much current difference (magnitude andd phase, of course) between the ends of a 100 ohm inductor at the base of that same antenna? Roy Lewallen, W7EL Cecil Moore wrote: Yuri Blanarovich wrote: Judging by description, I would guess that there wasn't much difference. The feedpoint of the radiator alone is 35-j185. The impedance of the loading toroid is 0.6+j193. Assuming perfect predictability, that gives the antenna system a feedpoint impedance of 35.6+j8, i.e. it is *longer* than resonant. That moves the current maximum point inside the toroid making the current in and out even closer to equal. If a coil is installed at a current maximum point or a current minimum point, the current in and out will be the same. If a coil is installed at a place where the slope of the current envelope is positive, the current will actually increase through the coil. |
#273
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I'll accept your prediction. It doesn't seem to correlate with your
disagreement with Ian that the current into and out of a lumped inductor are equal. You accused him of "mental masterbation" and being "seduced by the steady state model" for even thinking such thoughts. I also asked you a while back if we should expect a very small inductor to act the same when connected at the base of an antenna as when connected to a simple series RC or RL. Your response was that the analysis couldn't be done using conventional circuit theory, but required "distributed network analysis". Conventional circuit theory predicts equal currents going in and out, so from your response I had presumed that the fancier analysis would predict something else. You've also stated that the current shift through the inductor should equal the "electrical length" of the antenna "replaced" by the inductor. In this case, the inductor is "electrically lengthening" the antenna by either about 45 degrees, or about half that amount, depending on how you assign the effect of the mounting arrangement. So in the past, you've predicted no difference, something like 20 or 45 degrees phase shift, or an indeterminate amount. It's good to see you've settled on one figure. My inductor was placed at the antenna base because I could measure the currents there with reasonable accuracy. The inductor size was chosen to resonate the antenna, hopefully duplicating the situation reported by Yuri in his quote of W9UCW's measurements. On his web site, Yuri quoted W9UCW as measuring the currents at the ends of a toroid mounted at the base of the antenna as being 100 mA at the bottom and 79 at the top. You must, then, believe these measurements to be in error. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: Our educations differ a great deal. Mine enabled me to give a numerical prediction, which as anyone who has read my earlier postings, is 1. Yours has evidently not prepared you to meet this onerous challenge. Roy, I have repeated a statement three or four times earlier on this newsgroup. My statement predicts a result of 1. Here is that statement again: "If a loading coil is placed at a current maximum point, the current in and out of the coil will be equal." I have been assuming that is why your coil was placed at the current maximum point, to ensure that the currents would be equal. Depending upon where the coil is placed, the currents in and out of the coil can be equal, greater than, or less than. |
#274
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Yuri, the inductor I put at the base of the antenna "replaced" something
like 20 - 45 degrees, depending on how you judge the effect of the mounting arrangement. Barry, W9UCW also measured a substantial current magnitude difference between the ends of a base-mounted toroid. So, as a successful and award-winning engineer, what do you calculate as being the ratio of currents across my inductor, and how did you calculate it? Roy Lewallen, W7EL Tdonaly wrote: Yuri wrote, Our theory is that the current drop across the inductor should be roughly proportional to the current in the radiator (in degrees) that it replaces (Cosine law). That's a pretty good theory, Yuri. I'd like to know where you got this "Cosine law" you keep talking about. I can't seem to find mention of any such _law_ anywhere but on this newsgroup. Does that mean I should throw away my method of moments software because I don't need it any more? And what is a current drop? I've heard of voltage drops and cough drops but never current drops. Finally, how do you measure the "current in the radiator (in degrees)?" Why not use amperes like everyone else? I won't believe your theory, Yuri, until you and Cecil take the time to present it in terms of field theory. Since you guys have taken EM classes in college you should have no trouble doing this, right? 73, Tom Donaly, KA6RUH |
#275
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Roy Lewallen wrote:
Can I conclude from this that if I were to make a coil with more or less inductance, then I would see a current difference between the ends of the coil? So tell you what. If you'll pull out your equations and calculate the expected current difference, I'll replace the coil with one of 100 ohms reactance and remeasure. How much current difference (magnitude andd phase, of course) between the ends of a 100 ohm inductor at the base of that same antenna? I know you are not that naive, Roy. I have said many times over the past few days that if you locate a coil at a current maximum point, the current will be approximately equal at each end. So what did you do? You locate your coil at a current maximum point and I assume your measurements proved me to be correct. As long as you install the coil at the base of the antenna, the currents are guaranteed to be close to equal as I have said any number of times. If you place the coil at a location where the slope of the current is maximum and positive, the current through the coil will *INCREASE*. If you place the coil at a location where the slope of the current is maximum and negative, the current through the coil will decrease. This is typical of center-loaded mobile HF antennas. Incidentally, Kraus engages in some of your alleged "pseudo-analysis" in his book. He clearly shows the current drop through loading coils. He even says a coil can be used to shift the current by 180 degrees. Come to think of it, my 440 MHz mobile antenna has a coil in the center that shifts the current by 180 degrees yielding considerable gain from those two phased elements. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#276
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I've uploaded a closeup photograph of the inductor and current probes to
my web site. You can view it at http://eznec.com/rraa/Inductor_Current_Measurement.html. Roy Lewallen, W7EL |
#277
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Roy Lewallen wrote:
I'll accept your prediction. It doesn't seem to correlate with your disagreement with Ian that the current into and out of a lumped inductor are equal. You accused him of "mental masterbation" and being "seduced by the steady state model" for even thinking such thoughts. Yes, for center-loaded electrical 1/4WL mobile antennas, that is true. You seem to be protecting the same sacred cow as Ian. For the sixth time: If a loading coil is located at a current maximum or current minimum point, the current into and out of the coil will be approximately the same. If a loading coil is located where the slope of the current is positive, the current will actually increase through the coil. If a loading coil is located where the slope of the current is negative, the current will decrease through the coil. This is typical of center- loaded mobile HF antennas. Conventional circuit theory predicts equal currents going in and out, so from your response I had presumed that the fancier analysis would predict something else. Not if the coil is located at a current maximum or current minimum point. How many times do I have to say that before it soaks in? You've also stated that the current shift through the inductor should equal the "electrical length" of the antenna "replaced" by the inductor. In this case, the inductor is "electrically lengthening" the antenna by either about 45 degrees, or about half that amount, depending on how you assign the effect of the mounting arrangement. Nope, it isn't. You antenna is somehow already loaded and is equivalent to a 50 foot unloaded antenna. Your feedpoint reactance should be around +j370 for an unloaded antenna so you have about 27 degrees of extraneous loading somewhere. So in the past, you've predicted no difference, something like 20 or 45 degrees phase shift, or an indeterminate amount. It's good to see you've settled on one figure. There are three possibilities listed earlier. What happens with a coil depends upon where it is located. Please read that over and over until it soaks in. My inductor was placed at the antenna base because I could measure the currents there with reasonable accuracy. Yep, you are looking for your keys under the streetlight because the light is better there than it is where you really lost the keys. On his web site, Yuri quoted W9UCW as measuring the currents at the ends of a toroid mounted at the base of the antenna as being 100 mA at the bottom and 79 at the top. You must, then, believe these measurements to be in error. If the toroid is not mounted at a current maximum point, i.e. if the feedpoint impedance is slightly capacitive, then those figures could be accurate. I didn't pay any attention to them. Could be his coil causes a larger phase shift than your coil. You making your antenna too long ensured that the current maximum point would fall inside the coil. Whether you realize it or not, you are biasing the outcome of your experiment to agree with your pre-conceived (sacred cow) notions. Please note that I am not defending everything Yuri and W9UCW have said so don't treat that set of three people as a lumped constant. I am not guilty by association. My postings stand on their own merits or lack thereof. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#278
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Tdonaly wrote:
"He doesn`t say a single thing about a "cosine law" for a real antenna...." Like Cecil, I didn`t either, but I am surprised a challenge exists to sine or cosine current distribution which most serious antenna authors assume and illustrate. If the projected height of of a sine wave is cast upon a circle, its amplitude is completely described by the projection of the radius on the diameter of the circle. A sine wave amplitude is the vertical or "y" value of the (x,y) coordinates of the tip of a radius vector rotating counter-clockwise in a circle of unit value. The angle considered is that made by the radius vector with the "x" axis. Antenna discussions often use cosine waves. These are identical to sine waves except that they are displaced by 90-degrees, or 1/4-cycle, or pi radians (all different names for the same thing). When sine equals +1, the cosine equals 0-degrees, and it is about to go negative. This is because the sine starts at a value of zero at zero degrees. At the same 0-degree start, cosine is +1. There is no difference between a sine and a cosine wave except for 90-degrees phase lead of the cosine wave. The sine of an angle is the same as the cosine of (that angle minus 90-degrees). Example: sine of 90-degrees = 1. Cosine of 0-degrees = 1 also, etc. etc. etc. Ed Laport in "Radio Antenna Engineering" says on page 19: "The principles of the electrically short antenna are better understood from Fig.1.1, in which the natural sinusoidal current distribution along a straight uniform section quarter-wavelength vertical is used for reference. A straight uniform vertical antenna with a height of 20 degrees would have the relative current distribution shown for the sine curve above the 20-degree level A." And in John Devoldere, ON4UN`s now famous Fig 9-22: "Short loaded verticals with their current distribution." Note the cosines given for each antenna height demarcation. Best regards, Richard Harrison, KB5WZI |
#279
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Roy Lewallen wrote:
Yuri, the inductor I put at the base of the antenna "replaced" something like 20 - 45 degrees, Nope, it didn't, Roy. Your 33' vertical was already equivalent to a 50' vertical apparently due to extraneous loading. I calculate that your coil replaced 18 degrees of wire with a current maximum point located inside the coil. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#280
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Ah,
So now you're saying that any coil at the base of a short vertical antenna, regardless of its value, will have equal currents at the input and output? Ok, suppose I make the measurement at, say, 10 MHz, where the coil is no longer at the current maximum. Tell you what. I'll set up a 33 foot wire vertical, to eliminate the difficulty of the mounting arrangement. I'll furnish you the base impedance at 10 MHz, and even let you choose the inductor value. Be sure and choose a value that will clearly illustrate your point. Using the fine education you received from Balanis et al, calculate the current into and out of the inductor (phase and magnitude), and I'll set it up and measure it. Since it is a fair amount of work on my part, though, I'd like to do a dry run first, using, say, the base impedance predicted by EZNEC. Then, after you've shown us how you make the calculations, I'll build the antenna and do the measurement. I'd hate to go to the considerable trouble of setting it up and find that you somehow aren't able to do the calculation. Other predictions would be welcome, too, such as Yuri's, based on the "missing antenna length" theory of inductor currents. Better yet, you can do the measurement yourself. As you can see from the picture I just posted to my web site, the measurement ain't exactly rocket science. I don't have much time to burn, but still shook loose enough to set it up. Anybody with a two channel scope, a soldering iron, and a signal generator or transmitter can do just what I've done. You can too. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: Can I conclude from this that if I were to make a coil with more or less inductance, then I would see a current difference between the ends of the coil? So tell you what. If you'll pull out your equations and calculate the expected current difference, I'll replace the coil with one of 100 ohms reactance and remeasure. How much current difference (magnitude andd phase, of course) between the ends of a 100 ohm inductor at the base of that same antenna? I know you are not that naive, Roy. I have said many times over the past few days that if you locate a coil at a current maximum point, the current will be approximately equal at each end. So what did you do? You locate your coil at a current maximum point and I assume your measurements proved me to be correct. As long as you install the coil at the base of the antenna, the currents are guaranteed to be close to equal as I have said any number of times. If you place the coil at a location where the slope of the current is maximum and positive, the current through the coil will *INCREASE*. If you place the coil at a location where the slope of the current is maximum and negative, the current through the coil will decrease. This is typical of center-loaded mobile HF antennas. Incidentally, Kraus engages in some of your alleged "pseudo-analysis" in his book. He clearly shows the current drop through loading coils. He even says a coil can be used to shift the current by 180 degrees. Come to think of it, my 440 MHz mobile antenna has a coil in the center that shifts the current by 180 degrees yielding considerable gain from those two phased elements. |
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