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Cecil Moore wrote:
Jim Kelley wrote: Cecil Moore wrote: We have been told that lumped inductors have zero phase shift. I think the claim is that there is zero current differential in magnitude across a lumped inductor. It's certainly true of a pure inductor. Presumably, one in which radiation is not a factor, and for which the electrical length is short compared to wavelength. For a lumped inductance, the electrical length is zero. Presumably, that has a zero effect on the current. Assuming that only the voltage is affected, the phase relationship between the voltage and current is blown compared to an unloaded antenna. But the relationship is somehow (magically?) restored by the time the end of the antenna is encountered. Exactly how is that relationship restored? The problem seems to be caused by the assumption that an inductor has no current lag in an antenna circuit. In my experience, lumped circuit elements are just a simplified way of expressing the characteristics of device that has distributed reactances and resistance. You draw the equivalent circuit as inductors, capacitors, and resistors in series and shunt where appropriate, and assign the appropriate values to each. You can do that just as easily with an antenna as with a transformer. In the case of a loading coil, perhaps you could say that a portion of the "lumped" inductance of the antenna is replaced with a coil inductor. From a relative size standpoint, the inductance of the coil is certainly "lumped" compared the inductance of the rest of the antenna. But does size matter? :-) As Richard alluded, an inductor with zero phase shift must have zero inductance. I think it's safe to assume loading coils cause a phase shift. But what of the current differential? Seems difficult to believe that current can go from max to min, and impedance and voltage go from min to max along the 15" of a 40 meter hamstick whip. 73, Jim AC6XG |
On 06 Nov 2003 19:38:27 GMT, oSaddam (Yuri Blanarovich)
wrote: Hi Yuri, What is the problem with going back to a post and responding to that? Duplicated unnecessarily, but obviously needed: 100mA on an 8 Ampere full scale 3.5 inch meter is slightly more than 1% deflection (less than the width of the needle). The 100W excitation current levels near and through the model's solenoid exhibit values in the 1 Ampere region or at 12% deflection for an instrument that is arguably as accurate as 10%. This does not bode well for a compelling exhibition of any conclusive results. NOW, if I were wrong to presume that 100W is going to be the excitation - is that MY fault? If we jack up the power applied (easily within the means of an amateur so empowered, so to speak) then that region can certainly be forced into readings of vastly improved accuracy relative to the available metering. HOWEVER, this now inhibits doing the full length survey because the lower section would clearly overload the metering. You can't win for losing. Well, you can win if you are accomplished at the bench (a rare talent in this ivory tower where merit is weighed by angel population counts) by modifying your metering through shunts. I will warn you, however, it is incumbent upon you to reveal how that was accomplished, how it was confirmed and the data to support that too. You will also have to measure the surface temperatures and conspire to replicate them to your metering (something that you have not really responded to) to observe the systematic error introduced by these ever growing power applications. This, in a sense, is a turn of "you can't win for losing, but you can get close, but you still might lose anyway." Given your failure to respond/correct/aknowledge forced speculations, I had to cover many angles "implicit" in your vague specifications. You found an error, skipped the correct guess and still did not actually offer a hard specification. I have not done it yet. You have technical questions about W9UCW measurements and setup, ask him You haven't done what? I've asked how large the radiator, how large the coil, what size the radial field. WAS not WILL BE. All of these are fundamental questions for specifications that supposedly are part and parcel to your evidence and you ask ME to confirm the details? Why do you expect this to be compelling evidence that blows Tom out of the water? I did far more with a simple model that anyone could review for completeness' sake. You didn't responded to that! What's the program here? You left me to speculate about the model - NO RESPONSE to that either. What model? Hardware "model" W9UCW used was 60 quarter wave radials on ground (40m - see the picture) shorted radiator tuned to resonance with loading coil (see picture). Normal loaded antenna. Soft model by W5DXP was described by him. GAD! Why do you bother to come here for support? This all started with your avowed problem of Significant impact on modeling software. If the stuff is not accomodated properly, then results (mainly efficiency) are way off. Which had already been answered before you started this thread. You say so in your web page. 3 Days ago I offer my model that disputes Tom, supports you inferentially and you ask "what model?" Boy how lazy. OK, the plain vanilla radiator 93" tall (3/8" stock) in 93 segments surrounded by 60 X 93" radials (#12 wire) ALL elevated 6" above a real, medium ground. SRC DATA @ 7.1MHz = 0.7995 - J 810.9 ohms Current varies from 1A at drive point to 0 at tip The adornment consists of this underspecified coil being decimated and spread across 10 inches of space in the middle of the radiator with lumped values of 30µH each. For the life of me, I don't know what this exercise was to prove given the results: SRC DATA @ 7.1MHz = 1.258 - J 1561 ohms Current varies from 1A at the drive point to 0 at the tip One variation on the first pass design is that when this current hits the decimated inductor, the current drops to 0 a few inches before the first inductor section and quickly develops an 180° shift over those next few inches which persists on out to the tip. At the bottom of the coil sections, the current again picks up to roughly 100mA climbing to roughly 150mA at the top and then declining over the remaining length of radiator. It would seem that anyone could craft any assortment of conditions to support any of a dozen new theories from this kind of legerdemain. If there are ANY details that are wrong, I haven't seen one syllable written by you to the matter. I would point out that nothing about this model quoted above resonates in spite of your assertion that it did for the hardware tested. You never read this did you? I said that W9UCW set the drive level to show 100 mA deflection on the bottom meter, to eliminate errors you worried about, can't get any better than full scale deflection. The objective was to see the how much current decreases from the bottom to the top of the coil. Is it +-0 as Tom camp claims or is it significantly more like around 50% we found and claim. How is that terribly wrong that would prove Toms are right? Have you actually read any of my posts? You describe the enormous heat issues that come with these characteristics that have been UNRESPONDED to. Huh? I mentioned heat effect, where "lousy" Hustler coil demonstrates more heat generation at the bottom than at the top, therefore higher current at the bottom than at the top. What's wrong with that and conclusion that there must be more current flowing in the bottom turns than in top turns? Huh? Can you elaborate? Yuri, it is your statement that begs elaboration. Do you have data that supports nitpicking in the .01 area of significance - obviously not. What has bottom third of the coil heating up from the current (no meters) has to do with caloric based measuring device? You are now removing the frog's legs to prove it is deaf? You stick heat sensitive strip on the coil you will see the rapid change of colors going from the bottom to the top. What is wrong with that? Do you know how that ammeter works? You have here, and repeatedly, offered a description of considerable heat. The RF Ammeter works on the basis of heat (that's why it is called a thermocouple type). It is in close proximity to a source of heat by simple observation of the photos offered and undoubtedly what you anticipate in repeating at elevated power levels (more heat). What more does it take to suggest this heat is a source of error? 88's Yuri Blanarovich, K3BU still waiting for ONE PROPER MEASUREMENT, hellooooo???? otherwise you flat earth (er equal loading coil current) believers are the ones flying in the la-la land. Still waiting for you to 1.) provide a complete specification of the a.) radiator b.) solenoid c.) ground d.) drive applied (not readings) 2.) respond to the model offered; 3.) describe the errors possibly attending all this heat. Do I get real technical specifications OR should I be applauding? Please tell me what form of support you expect. 73's Richard Clark, KB7QHC |
Richard Clark wrote:
You are now removing the frog's legs to prove it is deaf? Cricket's leg, Richard, cricket's leg. Still waiting for you to 1.) provide a complete specification of the a.) radiator b.) solenoid c.) ground d.) drive applied (not readings) 2.) respond to the model offered; 3.) describe the errors possibly attending all this heat. Too bad you don't hold the other side to the same standards. One wonders why. Others asserted the positive premise. Why is it not up to them to prove their assertions? Why is it up to Yuri to disprove the positive assertions by others that triggered this entire discussion? You're not prejudiced, are you? -- 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! =----- |
Jim Kelley wrote:
Seems difficult to believe that current can go from max to min, and impedance and voltage go from min to max along the 15" of a 40 meter hamstick whip. Not difficult at all for True Believers of Old Wives' Tales or hams seduced by the steady-state model. :-) Component energy waves don't matter, don'tcha know? Never mind that standing waves are probably impossible without forward waves and reverse waves. -- 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! =----- |
The time I am spending arguing here, I will be better off to do my own
measurements and start to write the article. I think this is about what I needed, I have got the picture, explanation for what are we seeing, its time to put it all together. I will just comment on your ending comments, unless I see any serious and measured arguments, further arguments are just running around in circles. Do you know how that ammeter works? You have here, and repeatedly, offered a description of considerable heat. The RF Ammeter works on the basis of heat (that's why it is called a thermocouple type). It is in close proximity to a source of heat by simple observation of the photos offered and undoubtedly what you anticipate in repeating at elevated power levels (more heat). What more does it take to suggest this heat is a source of error? I know how ammeters work. I key the TX, the ammeter almost instantaneously shows the current. W9UCW used good quality coils that would not heat up with 100 mA current. No time for coil to get red hot and fry the meters. You can see that from the pictures. I mentioned Hustler coil, wound with small gage aluminum wire and have experienced heating of the bottom with no meters screwing it up or vice versa. I put 500 W to it and saw that heatshrink tubing fried at the bottom = more current there, no meters to show error. So what's the horrendous heat got to do with what W9UCW measured? Try it, measure it. If I will do measurement I will not use Hustler aluminum coils but 1/4" tubing. Got that? 88's Yuri Blanarovich, K3BU still waiting for ONE PROPER MEASUREMENT, hellooooo???? otherwise you flat earth (er equal loading coil current) believers are the ones flying in the la-la land. Still waiting for you to 1.) provide a complete specification of the a.) radiator b.) solenoid c.) ground d.) drive applied (not readings) You pick typical mobile antenna, mount the coil from half way up, pick pair of radials or any ground, drive with what you have and see what you get. The objective is to prove or disprove that current across the loading is not the same, but more in the order of 50% drop with +/-10% error if you like. 2.) respond to the model offered; 3.) describe the errors possibly attending all this heat. Do I get real technical specifications OR should I be applauding? Please tell me what form of support you expect. 73's Richard Clark, KB7QHC As I said, you want to verify W9UCW measurements, contact him, I don't have ALL the details of his experiment. I will provide that info on my setup, when I get around to do it. What I expected? To see if anyone else measured the current in the coils and what they found, or if we are in error, where did we committed error and show us where we are wrong, if we are. (no one yet) I was looking for explanation of the effect. (thanks Cecil, makes sense) We found that software (EZNEC) does not treat the effect properly. We found that people learned that coil "must" have the same current and they will not accept reality and argue to death that it ain't so, if it is. I am happy to confirm that I was right, I found out about the effect and reasons behind it, opened my eyes wider and got me some ideas to improve loaded and mobile antennas. I corrected my opinion about reflected waves, I don't like them on feedlines, but I appreciate them on the radiators now (thanks Cecil). I found that presently we can approximate loading coil as a loading stub in the soft modeling (thanks Cecil) to get some more meaningful results rather than using imaginary coil. Unless someone shows that 7 points I raised are not valid, I am happy with results of this interesting exercise. Thanks all! Yuri |
Yuri Blanarovich wrote:
Unless someone shows that 7 points I raised are not valid, I am happy with results of this interesting exercise. Here's an interesting EZNEC result. I took the 102' loaded dipole that was resonant on 3.76 MHz and ran it on 14.3 MHz. I repositioned the loading coils at a current minimum point with a one ohm resistor on each side so there is 0.03 wavelength between resistors. --------------R1--coil1--R2-------FP--------R3--coil2--R4-------------- EZNEC sez: Current through R1 is 0.1618 amps at -156 degrees Current through coil1 0.09643 amps at -130 degrees Current through R2 is 0.08098 amps at -70 degrees In the ten degrees between R1 and R2, the current doubles and shifts phase by 86 degrees. Can we use these results to prove there is a phase shift through a lumped inductor? :-) -- 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! =----- |
Cecil Moore wrote:
Yuri Blanarovich wrote: Unless someone shows that 7 points I raised are not valid, I am happy with results of this interesting exercise. Here's an interesting EZNEC result. I took the 102' loaded dipole that was resonant on 3.76 MHz and ran it on 14.3 MHz. I repositioned the loading coils at a current minimum point with a one ohm resistor on each side so there is 0.03 wavelength between resistors. --------------R1--coil1--R2-------FP--------R3--coil2--R4-------------- EZNEC sez: Current through R1 is 0.1618 amps at -156 degrees Current through coil1 0.09643 amps at -130 degrees Current through R2 is 0.08098 amps at -70 degrees In the ten degrees between R1 and R2, the current doubles and shifts phase by 86 degrees. Can we use these results to prove there is a phase shift through a lumped inductor? :-) No. It'll take a lot more than an EZNEC analysis, or back yard measurement for that matter, to disprove theory that's been verified and used successfully for more than a century. Roy Lewallen, W7EL |
Roy Lewallen, W7EL, wrote: No. It'll take a lot more than an EZNEC analysis, or back yard measurement for that matter, to disprove theory that's been verified and used successfully for more than a century As I followed this topic thread both in this forum and on eHam, I formed my own opinion about the observed disparity between currents entering and leaving an antenna loading coil. My conclusion was that the parasitic capacitances between the coil turns and ground were responsible for shunting a fraction of this current away from the coil terminal that connects to the top part of the antenna (in the present case of a shortened, vertical monopole - the typical HF mobile antenna). To confirm this notion, I created the following EZNEC(tm) model of a 13-foot, inductively loaded monopole fed against a perfect ground: (1) a 3-ft bottom section containing the RF source, (2) a set of four inductors connected in series and occupying a physical length on the antenna of 2 feet, (3) a set of three "gimmick" wires attached to the internal nodes of the inductor assembly and extending horizontally for 2 feet that simulate the parasitic capacitances between the coil turns and ground and (4) an 8-foot whip on the top to complete the antenna. The operating frequency was chosen to be 3900 kHz and the inductors were adjusted in value to resonate the entire antenna at this frequency. The results are shown below as an EZNEC printout of the load data for the four inductors (Inductor 1 is the one closest to the bottom): EZNEC ver. 3.0 Yuri's Mobile #1 11/7/2003 6:05:04 AM --------------- LOAD DATA --------------- Frequency = 3.9 MHz Load 1 Voltage = 4280 V. at 89.99 deg. -- Current = 10.24 A. at -0.01 deg. Impedance = 0 + J 418 ohms Power = 0 watts Load 2 Voltage = 4144 V. at 89.98 deg. -- Current = 9.914 A. at -0.02 deg. Impedance = 0 + J 418 ohms Power = 0 watts Load 3 Voltage = 3756 V. at 89.97 deg. -- Current = 8.985 A. at -0.03 deg. Impedance = 0 + J 418 ohms Power = 0 watts Load 4 Voltage = 3125 V. at 89.97 deg. -- Current = 7.476 A. at -0.03 deg. Impedance = 0 + J 418 ohms Power = 0 watts Total applied power = 156.6 watts As can be seen, there is roughly a 25% reduction in current from bottom to top on the "loading coil". Interestingly, most of this current-shunting appears to take place near the top of the "coil". This model is admittedly quite crude. The conclusions I reached were that there was at least a qualitative effect from the parasitic shunting capacitances on the current flow through a loading coil and that quantitatively it appears to be fairly significant. I have included the text description of the model from EZNEC below: EZNEC ver. 3.0 Yuri's Mobile #1 11/7/2003 6:24:20 AM --------------- ANTENNA DESCRIPTION --------------- Frequency = 3.9 MHz Wire Loss: Zero --------------- WIRES --------------- No. End 1 Coord. (in) End 2 Coord. (in) Dia (in) Segs Conn. X Y Z Conn. X Y Z 1 GND 0, 0, 0 W2E1 0, 0, 36 0.1 8 2 W1E2 0, 0, 36 W3E1 0, 0, 42 0.1 1 3 W4E1 0, 0, 42 24, 0, 42 0.1 1 4 W2E2 0, 0, 42 W5E1 0, 0, 48 0.1 1 5 W6E1 0, 0, 48 0, 24, 48 0.1 1 6 W4E2 0, 0, 48 W7E1 0, 0, 54 0.1 1 7 W8E1 0, 0, 54 -24, 0, 54 0.1 1 8 W6E2 0, 0, 54 W9E1 0, 0, 60 0.1 1 9 W8E2 0, 0, 60 0, 0, 156 0.1 1 Total Segments: 16 -------------- SOURCES -------------- No. Spec. Pos. Actual Pos. Amplitude Phase Type Wire # % From E1 % From E1 Seg (V/A (deg.) 1 1 1.00 6.25 1 10 0 I -------------- LOADS (R + jX Type) -------------- Load Spec. Pos. Actual Pos. R X Wire # % From E1 % From E1 Seg (ohms) (ohms) 1 2 50.00 50.00 1 0 418 2 4 50.00 50.00 1 0 418 3 6 50.00 50.00 1 0 418 4 8 50.00 50.00 1 0 418 No transmission lines specified Ground type is Perfect Just to complete the picture, here is the Source data: EZNEC ver. 3.0 Yuri's Mobile #1 11/7/2003 6:48:30 AM --------------- SOURCE DATA --------------- Frequency = 3.9 MHz Source 1 Voltage = 16.43 V. at 17.66 deg. Current = 10 A. at 0.0 deg. Impedance = 1.566 + J 0.4984 ohms Power = 156.6 watts SWR (50 ohm system) = 31.937 I will be happy to send out the .EZ file for this to any interested parties. Splice together the e-mail address below to contact me. 73, Jim Bromley, K7JEB k7jeb (at) qsl (dot) net |
Roy Lewallen wrote:
It'll take a lot more than an EZNEC analysis, or back yard measurement for that matter, to disprove theory that's been verified and used successfully for more than a century. Nobody is out to disprove theory. But it seems apparent that the lumped inductor conceptual model and a real-world inductor have little in common. For the same reason, one cannot use a model of a lossless transmission line to determine real-world efficiency. Models do not dictate reality. It is supposed to be the other way around. -- 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! =----- |
Yuri, K3BU wrote:
"Point by point please." to a list of 7 facts supporting his contention that a non-uniform current exists in a 1/4-wave antenna with a loading coil inserted at a spot from 50 to 70% of the radiator length, on Wed. Nov. 5, 2003, 3:15 am (CST + 6). 1. Coil is warmer at bottom than top. As power dissipation is proportional to the square of the current, it shows that in a uniform structure heat is where the current is high. 2. Current indicators at the top and bottom of a loading coil show 40 to 60% difference in ends of the loading coil. High accuracy may not be available, but the argument is between same current or dissimilar currents at the ends of the coil. High accuracy is not needed. 3. Let`s look at the RF choke. It`s not what the coil is called. It`s position and size with respect to wavelength. 4. W9UCW used a toroid and got the same results. The results were based on phase delay, not coil radiation. Antenna current in a coil results from overcoming an opposition. This impedance is a vector sum of reactance and resistance. The reactance of the coil is the same in both directions of energy travel. The impedance the antenna presents at the ends of the coil is not the same in both directions. Any coil reactance produces a delay. Inductors used in telephone circuits to block audio and pass d-c and low-frequency ringing current are called "retardation coils". A delay time of the signal is called "phase lag". These are appropriate names. Toroid coils cause phase lag too. 5. Cecil explained the reflected wave situation and delay in the coil---. Cecil did it accurately and well. 6. ON4UN in his Low Band DXing book for years has shown and explained the distribution of current in various configurations of loading coils----etc. ON4UN did it right and it has stood the test of time. Don`t hold your breath waiting for revisions. 7. How could it be if the voltage (neon bulb test) is increasing along the coil towards the top, current has to be decreasing. Yes, unless the power is increasing in the same direction, and it`s not. The neon shows high potential gradient points. In the driven quarter-wave radiating element, loaded or unloaded, the maximum voltage always seems to be at the tip end. We know that as in a transmission line, in a standing-wave antenna, reflection produces current maxima at voltage minima, and vice versa. Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only shows there is not much to contradict. Best regards, Richard Harrison, KB5WZI |
Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only shows there is not much to contradict. Best regards, Richard Harrison, KB5WZI Hi Richard, thanks very much for the positive reinforcement. Seems that those who get their hands dirty from antenna grease know a thing or two, those who model their world on the computer know their paper stuff. So far not a one "overthrow" of my 7 points, so I take it that we are on the right track and hope that others get it too and help us to use it properly. BTW I just found good source for liquid crystal strip thermometers, they have them in the pet shops, they are used for aquarium temperature measurements cost around $2. Cheap and easy way to verify the heat from current. I will get some and run som visual tests on Hustlers. 73 Yuri |
K7JEB wrote:
I will be happy to send out the .EZ file for this to any interested parties. Splice together the e-mail address below to contact me. Good stuff, as usual, Jim. It comes as no surprise to me that a three dimensional component with distributed resistance, distributed inductance, and distributed capacitance changes the voltages and currents at each end of the component. The changes are accentuated in a standing-wave environment. And to improve on your model a tad, make the capacitive wires equal on each side of the installation point, i.e. instead of a 2 foot wire sticking out horizontally, make it one foot of wire sticking out in two opposite directions. That will minimize radiation from those wires. -- 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! =----- |
Cecil, W5DXP, wrote:
And to improve on your model a tad, make the capacitive wires equal on each side of the installation point, i.e. instead of a 2 foot wire sticking out horizontally, make it one foot of wire sticking out in two opposite directions. That will minimize radiation from those wires. Good suggestion, Cecil. I had planned to make the capacitive wires into little square-shaped contraptions having about the same size as a turn of wire on the loading coil and then duplicate them up and down in the Z direction. I may still do this, but I wanted to publish the preliminary results as soon as I saw an effect, however imperfectly perceived. Jim, K7JEB |
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However Yuri your experimenting supplies an advantage over the experts
in that it is in the real world that true invention has its value. Art I guess it is a sign of where "modern" technology and modeling is leading us - to the imaginary paper world. It just disturbs me that some of the "learned" people would not "lower" themselves to the reality, question the facts and adjust their "knowledge" out of the modeling world. As Cecil said, modeling supposed to model reality or close to it, not the other way around. In view of this exercise I am going to revise and investigate some of the topics I asked about here before. Looks like the "advice" I got might not be based on reality. I am sorry to see some of the "gurus" ridiculing and making snotty remarks, rather than pausing and stepping back to have a closer look or question or discuss it in a civil manner. Oh well, good thing it is only a hobby :-) 73 Yuri, K3BU |
Somehow I'm getting the image here of engineers sitting at their
computers, proposing lofty but unsupportable theories and modeling idealized but impossible circuits, while the tinkerers -- REAL MEN -- with grease under their fingernails, wrenches in hand, are designing and producing the practical items that REALLY WORK. Lemme tell 'ya. Those generators that make your power, those turbine blades that spin them. Those jet engines and airframes that get you across the country with nearly unbelievable reliability and safety. The little HTs you yak on. The signal generators, spectrum analyzers, oscilloscopes you use to make measurements. The marvelous ICs that do everything from running your microwave oven to being the guts of your PC. Those weren't designed by technicians or back room tinkerers. Those were designed by engineers who know and understand basic principles and how to apply them. Nearly anything designed in the last couple of decades has been extensively modeled before the first metal is cut, the first wire soldered, the first circuit board or IC produced. And when the extensively modeled airplane is built, it flies. The IC and circuit board work. They work by the thousands or hundred of thousands, despite tolerances, component variations, and temperature changes. Because they were modeled and they were understood. Not because somebody made one sorta work once on a workbench by experimenting. People who reject modeling as "paper stuff" and decry established theory have simply crippled themselves. It's their choice, but there's no reason to be proud of it. Part of the everyday work of an engineer involves making measurements of one sort or another. And it's when the results are surprising that you'll see the difference between someone who has a solid background in fundamentals and the person who doesn't. The former will work to resolve the surprising measurement results with known and trusted theory. The latter will question the theory, not having a solid background to build on. I've seen technicians quickly reject Ohm's law on the basis of a single careless measurement. From then on, that person has lost the ability to rely on a powerful principle, and can never be quite sure what kind of relationship to expect among voltage, current, and resistance. A person who does understand the principles will search for what errors or shortcomings have been made in the measurement process, or what simplifications have been made that aren't valid, will resolve them, and will learn from them. Let me give just one example from my own experience -- there've been scores like it over the years. Years ago, I was measuring the input impedance of a simple antenna (folded dipole, as I recall) through a one wavelength piece of coax. Assuming that the measured impedance was the same as at the antenna, the results were very different than modeling had shown. Some people, it seems, would have immediately posted the results on the web, challenging the modeling and transmission line theory, loudly and forcefully demanding that everyone who doesn't believe the results should immediately go out and make measurements. After all, that's proof, is it not, that the modeling is bunk and transmission line theory is bunk. Well, the reason for the strange results turned out to be coax loss. A bit of analysis (based on known principles) shows that even a small amount of transmission line loss will skew the measured Z toward the line's Z0. The effect is surprisingly strong when the impedance to be measured is quite different from the line's Z0, as it was in this case. Another thing I learned was that the coax I was using, a small diameter 75 ohm cable, was extraordinarily lossy at the low frequency of 7 MHz where I was making the measurements. I determined this to be due to the small center conductor, made of strands of tiny Copperweld wire. The copper coating was thick in terms of percentage, but thin in terms of skin depths at the low frequency because of the very small strand diameter. So current was flowing in the steel cores. I ended up learning two important things from the episode, which I've applied ever since to similar problems, and other ones too. If I were someone who was quick to throw out conventional theory or modeling results, I never would have learned from it, and I wouldn't be able to depend on either modeling or transmission line theory. Now, getting to the issue at hand. Those of us who studied and understood basic circuit analysis know that a vanishingly small inductor or any other two-terminal component must have equal currents in and out. When measurements show results that differ from this, it means -- to we who understand and believe the principles -- that either there's something we don't know about the measurement method that's skewing the results, or the approximation of a vanishingly small component isn't valid. Of course a lengthy inductor in an antenna isn't vanishingly small, and it also couples strongly to the antenna above and below it. So no one who understands basic principles would be the least bit surprised to find different currents at the inductor ends. However, the statement that significant current differences were found at the ends of an apparently small toroid aroused my curiosity. Either there's a peculiarity in the measurement, or there's a sneak current path, such as stray capacitance, accounting for the current imbalance. Being curious, I made some measurements of my own of a loading inductor at the base of an antenna. The details of the test are a bit lengthy, and this posting is already long, so I'll post it separately. I feel kind of sorry for people who are quick to abandon established principles each time a casual measurement -- or even a careful one -- seems to contradict them. They're pretty much doomed to randomly trying this or that, without ever having the hope of understanding what they're doing. It's just the sort of thing that gives rise to astrology and phrenology, as ways to try to understand the mysteries around us. I greatly prefer science, but each to his own. It is true that a person with marginal math skills might not be able to discover, let alone quantitatively prove, that coax loss was the culprit in the example I gave above. Without some background in math, as well as basic principles, it's not really possible to understand things on a very fundamental level. So a person without math skills is pretty much limited to general, rather than specific, understanding. As a footnote, I was a technician for quite a few years, first self taught, and later going through the Air Force radar technician school. I worked as a broadcast engineer, and repaired various equipment from radios, TVs, and telephone answering machines to heavy ground military radar. (I was, incidentally, regarded as being a very good technician. One reason was that I did firmly believe in the basic principles as I was able to understand them, and applied them whenever possible.) But I was often frustrated because I kept encountering things I didn't understand as fully as I wanted, which is why I ended up working my way (with a little help from Uncle) through engineering school. It gave me the theoretical and mathematical tools to understand a whole lot more about how things work, and on a much deeper level. I use modeling extensively, as do nearly all my fellow engineers, and I've been able to consistently design quality electronic equipment in a wide variety of categories -- by understanding and applying basic principles. Far from converting me to the effete theoretician I'm seeing caricatured here, the education and engineering experience has added immeasurably to my ability to understand this fascinating field. Roy Lewallen, W7EL Art Unwin KB9MZ wrote: oSaddam (Yuri Blanarovich) wrote in message ... Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only shows there is not much to contradict. Best regards, Richard Harrison, KB5WZI Hi Richard, thanks very much for the positive reinforcement. Seems that those who get their hands dirty from antenna grease know a thing or two, those who model their world on the computer know their paper stuff. Yuri you make a very good point there. Those skilled in the arts have often used gimmicks or quasi ruses in their studies especialy in the use of mathematics where one can show on paper that one plus one equals three but cannot prove it factually. Engineers also use imaginary things in the search of knoweledge where those that use their hands have to deal with the real world. For many inductance is pure but imaginary as is capacitance, each of these in the real world is a network but engineers with the help of Laplace have learned to deal with the real world with altered equations yet use the same name such as inductance which in the real world there is no such thing. The fact that you used an imaginary term such as inductance instead of a network unfortunately placed you in their camp in the world of imagination. An example with respect to your subject is for you to ask them to provide you with an inductance of unlimited Q which in the imaginary world that they frequent is no big deal, where in the real world you are finding that Q beyond a 1000 is nigh impossible. Since speach itself cannot resolve factual things to the satisfaction of all then their will be no resolution. All this reminds me of a problem I had years ago when I reffered to capacitive coupling where its inherrent inductive component can be used for matching purposes. Now you tell me how you can convince experts that a capacitor is a network and thus has a usefull inductance component when they see for mathematical reasons that the word capacitance refers to an imaginary term to describe what cannot be in the real world? However Yuri your experimenting supplies an advantage over the experts in that it is in the real world that true invention has its value. Art |
Here are some preliminary details about the inductor current measurement
I made. My antenna isn't nearly as ideal as the one Yuri described. (But if my results are different from the ones reported at the web site Yuri referenced, I'll be eager to hear why.) It's about 33 feet high, and has only 7 buried radials. The feedpoint impedance indicates a loss of about 25 ohms at 7 MHz, so I'd expect it to be a bit more at 3.8. It's bolted to a galvanized fence line post which protrudes nearly four feet from the ground, with spacing between the antenna and the post of about 1/4". This mounting has only a minor effect on the feedpoint impedance at 7 MHz, which is the antenna's intended frequency of use. It's quite profound at 3.8 MHz, though. The expected 370 or so ohms of capacitive reactance is transformed to 185, while the feedpoint R is 35 ohms, not far from the expected value. So the overall feedpoint Z is 35 - j185 ohms at 3.8 MHz, measured with a GR 1606A impedance meter. (I found that my MFJ 269 was about right with the X, but measured R as zero -- apparently the combination of low frequency and large X is a problem for it in resolving the R.) So I built an inductor with measured impedance of 0.6 + j193 ohms. It's 26 turns on a T-106-6 toroid core. Q is a bit over 300. This was placed in series at the antenna feedpoint. For current measurements, I made two identical current probes. Each one consists of 10 turns wound on an FT-37-73B ferrite core. The two leads from the winding are twisted and wound in bifilar fashion on another FT-37-73B core, 10 turns. This is then connected to an oscilloscope input via a two-foot (approx.) piece of RG-58. A 50 ohm termination is also at the scope input. This gives the probe a theoretical insertion impedance of 0.5 ohm. While making the measurements, I moved, grabbed, and re-oriented the coax cables, with no noticeable effect. This gave me confidence that the outsides of the coax weren't carrying any significant current. One probe went to each channel of the scope. I left the two scope inputs in the cal position, put both probes on the wire at the input end of the inductor, and recorded the p-p values with the scope's digital measurement feature. Then I reversed the order of the probes and remeasured. I found a slight prejudice toward the probe closest to the source -- 1.2% in one ordering, and 2.1% in the other. Averaging the two channels, though, showed them to be the same within less than 1%. (Each probe was always connected to the same scope channel, so this is a test of the probe-scope channel combinations.) Then I moved one probe to the output side of the inductor, and measured input and output current. And I reversed the probe positions on inductor input and output. The ratio of output to input current in the two tests differed by only 1.4%. When I encounter an astrologist, they invariably ask what "sign" I "am", then proceed to tell me how my personality meets their expectations. So what I do instead is to have them tell *me* what "sign" I "am" *first* -- which they should easily be able to do, based on my personality. Well, they don't find that to be fair, for some reason (although I certainly find it amusing). And so, I doubt if the following challenge will be regarded to be fair, for much the same reason. Those with alternative rules for solving circuit problems are challenged to predict what the ratio of output current to input current will be. I'm particularly targeting Cecil, and others who have bandied about a lot of pseudo-analysis about electrical length, reflections, and the like. And, Richard (Harrison), who said something like "an inductor without phase shift is like". . . I don't recall. . .hot dog without ketchup or something. Pull out your theories, and calculate it, like any competent engineer should be able to do. For cryin' out loud, it's a simple series circuit (except for Cecil, where it's some kind of distributed thing). First post your answers, then I'll post the result of my measurements. Roy Lewallen, W7EL |
Roy Lewallen wrote:
Pull out your theories, and calculate it, like any competent engineer should be able to do. For cryin' out loud, it's a simple series circuit (except for Cecil, where it's some kind of distributed thing). First post your answers, then I'll post the result of my measurements. What is the value of the distributed capacitance between each two turns on the toroid? That distributed capacitance is what makes a 75m mobile loading coil act like a transmission line. Question: Why didn't you use a 75m bugcatcher coil for the experiment? -- 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! =----- |
Roy Lewallen wrote:
I'm particularly targeting Cecil, and others who have bandied about a lot of pseudo-analysis about electrical length, reflections, and the like. Balanis would be surprised to know that you consider the material that he teaches in his classes at ASU to be pseudo-analysis. Some of the stuff I have posted is in Balanis' book, _Antenna_Theory_ which you haven't read. In particular, he says: "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forwards and backwards) as represented by traveling wave currents If and Ib in Figure 10.1(a)." I'm just wondering how you can be so sure that what I have offered is pseudo- analysis and which of the following statements you disagree with. Please be specific. 1. The feedpoint impedance of a typical traveling wave antenna is in the hundreds of ohms since there are no reflected waves. 2. The feedpoint impedance of a standing wave antenna is the result of superposition of forward and reflected waves (which cause the observable standing waves). 3. At the feedpoint of a 1/2WL resonant dipole, the forward current, reflected current, and forward voltage are all in phase. The reflected voltage is 180 degrees out of phase. This results in a purely resistive low-voltage/high-current ratio for the feedpoint impedance. 4. The above relationship is true for any dipole, 1/2WL or physically shorter, that has a purely resistive feedpoint impedance. (No resistive loading) 5. The phases of the signals at the feedpoint are known. The phases of the signals at the open tips of the dipole are known. Any loading used in order to increase the electrical length to 1/2WL must maintain those known phase conditions in order to achieve a purely resistive feedpoint impedance. On page 18, in Figure 1.15, Balanis shows how a 1/2WL dipole is achieved by flaring out the last ~1/4WL of an unterminated transmission line. He says: "As the section of the transmission line begins to flare, it can be assumed that the current distribution is essentially unaltered in form in each of the wires." -- 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! =----- |
My challenge to you was rhetorical. Based on past experience, I had no
real expectation that you'd be able to actually calculate a current. 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. Does anyone else feel up to the task of calculating the currents in a simple circuit? It used to be that you'd have to be able to do this to get a first phone license, or probably an amateur extra. Now, it appears that even American engineering education isn't always up to the task. Roy Lewallen, W7EL Cecil Moore wrote: . . . Balanis would be surprised to know that you consider the material that he teaches in his classes at ASU to be pseudo-analysis. Some of the stuff I have posted is in Balanis' book, _Antenna_Theory_ which you haven't read. In particular, he says: "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forwards and backwards) as represented by traveling wave currents If and Ib in Figure 10.1(a)." . . . |
Roy Lewallen wrote:
My challenge to you was rhetorical. Based on past experience, I had no real expectation that you'd be able to actually calculate a current. Here's how to mask the effects that we have been discussing: 1. Choose a small inductance that replaces a very small number of degrees of the antenna. 2. Use a ferrite coil designed to minimize distributed effects. 3. Mount the coil at a place in the antenna where the slope of the current is virtually zero. That's what you have done. Here's how to showcase the effects that we have been discussing: 1. Chose a large inductance that replaces an appreciable number of degrees of the antenna. 2. Use a typical air-core loading coil like a bugcatcher that has appreciable distributed effects. 3. Mount the coil at the center of the antenna where the slope of the current curve is near maximum. When you perform your experiment with an 8 foot center-loaded bugcatcher on 75m, then you will be taken seriously. -- 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! =----- |
W5DXP wrote to W7EL:
Question: Why didn't you use a 75m bugcatcher coil for the experiment? And why did you put toroid at the base? We are talking about loading coils that are installed at half to 2/3 up the radiator. Try 12 foot radiator with loading inductor at ~65% up from the feedpoint. The results should be "magnified". 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). Judging by description, I would guess that there wasn't much difference. Put that coil up but don't use scope probes, they will detune the antenna, no wires, use thermocouple meters. Probes at the base they probably do not distort the measurements much. Nice disertation on engineers and modeling. The only small problem is what and how you model. If your modeling uses 0 size inductance and real measurement shows something else, maybe there is a reason to question modeling how well it reflects reality. I went to university first, I designed parts that human life depended on, and I would think twice about relying on some numbers without testing and verifying it. Space shuttle tiles modeled OK? Yuri |
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. -- 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! =----- |
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. -- 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! =----- |
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 |
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 |
Tdonaly wrote:
And what is a current drop? I've heard of voltage drops and cough drops but never current drops. It's is the decrease in current due to the attenuation (alpha) factor in equation 1.22 (2) in Ramo, Whinnery, & Van Duzer. It's all covered in any distributed networks course. According to Balanis, antennas have an attenuation factor due to radiation and is similar to (slightly more complicated than) this familiar transmission line equation for lossy lines. I = Im(e^-az)d^j(wt-bz) where a is alpha, w is omega (2*pi*f), and b is beta (phase factor). 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? Please reference Chapter 1 of _Fields_and_Waves_... by Ramo, Whinnery, and Van Duzer. Start with equations 1.18 (4)&(5) and 1.22 (1) & (2). Also _Antenna_Theory_ by Balanis, equations 4-81 and 10-1 and one other that I cannot locate right now. :-) The one I cannot locate is the simplified one for a 1/2WL dipole. -- 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! =----- |
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? Please reference Chapter 1 of _Fields_and_Waves_... by Ramo, Whinnery, and Van Duzer. Start with equations 1.18 (4)&(5) and 1.22 (1) & (2). Also _Antenna_Theory_ by Balanis, equations 4-81 and 10-1 and one other that I cannot locate right now. :-) The one I cannot locate is the simplified one for a 1/2WL dipole. -- 73, Cecil http://www.qsl.net/w5dxp I don't have Ramo et al's book, but I do have Balanis' book. I think anyone who wants to understand equation 4-81 should read the whole section: 4.5.6 where he makes it clear these equations are approximations that are pretty good under some circumstances and lousy under others. The standards he judges them on are the techniques of Integral Equations and Moment Method which he explains in another part of the book. He doesn't say a single thing about a "cosine law" for a real antenna, as Yuri does. I think I'll keep my EZNEC. 73, Tom Donaly, KA6RUH (P.S. I looked, in Balanis, for a section on inductively loaded antennas and couldn't find one. That doesn't mean it doesn't exist. If anyone knows where to look in that book for information on such I'd be obliged for the information.) |
Tdonaly wrote:
He doesn't say a single thing about a "cosine law" for a real antenna, ... I didn't say a single thing about a "cosine law" either. If anyone knows where to look in that book for information on such I'd be obliged for the information.) Information on inductively loaded antennas seems to be sadly lacking. But I have found one in _Antennas_ by Kraus & Marhefka, third edition. I trust that will be a good enough reference for everyone. On page 823 under "23-13 TRAPS", what he says about traps is not relevant. But what he says about traps on half their resonant frequency is absolutely choice. "At frequency F1, for which the dipole is 1/2WL long, the traps introduce some inductance so that the resonant length of the dipole is reduced." On the next page, the current distribution is shown for the trapped dipole on 1/2 the trap's resonant frequency. Needless to say, it clearly shows a current drop through the inductive trap. And talking about phasing using coils: "A coil can also act as a 180 degree phase shifter as in the collinear array of 4 in-phase 1/2WL elements in Fig. 23-21b. ... THE COIL MAY ALSO BE THOUGHT OF AS A COILED-UP 1/2WL ELEMENT." Emphasis mine. Now you guys can stop pulling our legs and confess that it was all a joke. -- 73, Cecil http://www.qsl.net/w5dxp "One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike ..." Albert Einstein -----= 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! =----- |
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 |
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. |
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. |
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 |
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! =----- |
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 |
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! =----- |
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 |
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! =----- |
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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