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Yuri Blanarovich wrote:
My "case" is to bring this to attention of those who are still "knowing" that the current in loading coils is the same at both ends. The current can be the same at both ends if the coil is positioned at a current minimum or current maximum point which is NOT the case with mobile antennas. The key to understanding is to recognize that the coil causes the opposite phase change in the forward current as it does in the reflected current so they *cannot* track each other 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! =----- |
Tdonaly wrote:
What is "the radiating part of the antenna," Yuri? The part of the antenna under the ideal top hat. -- 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! =----- |
What happens when the coil is a flat pancake ?
--- Reg. |
What happens when the coil is a flat pancake ? --- Reg. It tastes good :-) Wouldn't make a difference. W9UCW used toroid and got the same results. Have you read the article? Yuri |
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Reg Edwards wrote:
What happens when the coil is a flat pancake ? Don't you have a program for predicting the electrical characteristics of a flat pancake coil? :-) Seriously, what are those characteristics? Is there a formula? -- 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! =----- |
NM5K:
At the base, there is not much difference, just like in cosine of the angle corresponding to the electrical length of radiator at that point. I'm not sure what you mean by this. Do you mean the current across the coil would be more steady than if the coil were higher? Does this include using the top loading wires? It is roughly like this: Consider quarter wave vertical (90 degree radiator), no coils or loading, you will get current max at the base and then diminishing towards the end to zero. Distribution is in the form of cosine function, nice cosine curve. Now if you would insert the coil anywhere in that radiator and shorten it and tune it back to resonance, the current distribution accross the coil would correspond to the "missing" portion of the radiator that coil replaces. Efficiency of the antenna is roughly proportional to the area under the curve. ON4UN pictures show that. Appears that the best compromise position for the loading coil is about 2/3 from the base. Having top loading, it "stretches" the high current carrying portion of the radiator. The lower the loading coil is, the less difference in current drop accross the coil (cosine function) but shortening of the more current carrying radiator - less efficiency. Again, this subject of current distribution is important in optimizing the antenna design by fine tuning the position of the loading coil in the antenna, combination with top loading etc. Morew current flowing in the radiating part of the antenna - the stronger the field and louder signal. Sure. But this is old news. I beat Reg's vertload program to death finding the best overall coil height for my mobile antenna. Basically I ended up putting it as high as I could. Which ended up a center load at 5 ft up, with a 10 ft whip. Or 8 ft up on a 13 ft whip when parked, and using the "Super" mode...:) That perhaps points to some error in validity of the formula, and confirms our findings. Experience and W5DXP reported shootout results point to reverse dimensions, 10 feet mast and 5 ft whip, coil about 2/3 up the antenna. You want to have as much as possible the mast length and then best compromise between the coil inductance (properties) and remaining whip (and hat). The "linear" current distribution mentioned in ARRL Compendium and Antenna Book is the simplification propagated from Belrose's 1955 QST article. It is close, but not exact and introduces confusion as it is demonstrated by the flat earth society. Dunno, I've never read it. Maybe calling the distribution as "linear" is the wrong term, but the current is still fairly steady along the radiator in the case of the vertical with the large top hat. I'm looking at a model of one now. The current distribution is almost like a twin tower standing next to the vertical. There is a slight decrease from bottom to top, but it's very small. It's still my view that the difference in current at each end of the coil used in such a case is fairly small. No matter where the coil was mounted. I've never said they would be exactly the same. Seems to me I started off by saying they could vary a bit depending on the antenna. So if you are saying they would be close, but not exact, you seem to be saying the same thing I said to begin with, which seems to be the same thing Cecil is saying. ??? Crap, I'm becoming confused.... I'm not good at playing these type games. That's why I didn't even bother reading the "current war" over on e-ham. *Sounds* like a 598 thread nit pick contest just judging from what I've heard... It's not "that" important to me, being I don't see what it would do for me, even if I found there to be a fairly large difference from each end. If you have pertinent info which shows the current is not even close to being constant across the coil, please enlighten us. "I guess you are attempting to" But at this point, I think everyone is starting to chase their tales and bark at the moon. I'm not really seeing the point, being the art of improving current distribution in short verticals using coil placement is old news. MK Well, looking at fairly simple example of typical 40m loaded mobile model antenna, as W9UCW used, having current vary 40 to 60% is significant, measured differences in field strength are in order of 10 dB and that is significant. I guess it must be like religion, you believe what you want and if the reality doesn't matter, than let everybody be happy. But this has tremendous impact on modeling especially in loaded parasitic arrays. If W8JI showed that Eznec calculated current to be different by fractions and the measurements show around 50% difference, then we have huge discrepancy and warning not to rely on results like that. There is too much reliance now going on modeling program results, ignoring some realities. Some people are becoming "experts" on antennas based on modeling results, without building one. But, even lightbulb can radiate and make some people happy, but it is not my intention to argue with those. My goal is to maximize the performance of the antenna and take advantage of propagation modes for maximum results in the contests, where every fraction of dB counts. It just amazes me that some people go to great length to speculate, calculate, rather than go and verify the measurements and see what it REALY is. You can see that in the threads after the articles. What I was looking for is to see 1. if anyone else MEASURED the current in loading coils, and what results they arrived at (and if we are wrong, then where did we go wrong). 2. If this is right than to have modeling software implement it with least error. I would like to use that for optimizing, say, loaded elements for receiving arrays on low bands, optimizing mobile antennas, loaded multielement beams, etc. Yuri, K3BU/m |
Mark Keith wrote:
I've never said they would be exactly the same. Seems to me I started off by saying they could vary a bit depending on the antenna. So if you are saying they would be close, but not exact, you seem to be saying the same thing I said to begin with, which seems to be the same thing Cecil is saying. ??? Nope, not what I am saying at all. I'm saying the magnitude of the forward current doesn't change much through the coil and the magnitude of the reflected current doesn't change much through the coil. That satisfies Kirchhoff. But the net current, which is the superposition of those two currents, can change drastically because of the relative phase differences on each side of 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! =----- |
Current through a coil in an antenna.
If we feed an antenna at the current point, the current decreases as the voltage increases along the antenna element from feed point to end.. That being said, a coil replacing a segment of an antenna (in order to physically shorten it) will exhibit the same properties (relating to currents) as the segment it replaced. "Richard Clark" wrote in message ... On 30 Oct 2003 22:59:26 GMT, oSaddam (Yuri Blanarovich) wrote: If we suppose the loading coil is heating up equally Hi Yuri, You have already testified twice that it does not - so why IF it around? 1.) If you trasmit for short period of time (not enough for heat to equalize) and feel it, or use thermal strips to check temperature, you would see the taper in the current from bottom to top. It is in order of 50%, not negligible. 2.) Put 500W to it for longer period and watch the heatshrink tubing shrivel from the bottom up. 73's Richard Clark, KB7QHC |
w4jle wrote:
Current through a coil in an antenna. If we feed an antenna at the current point, the current decreases as the voltage increases along the antenna element from feed point to end.. That being said, a coil replacing a segment of an antenna (in order to physically shorten it) will exhibit the same properties (relating to currents) as the segment it replaced. Yep, if the feedpoint impedances are the same and both are lossless, that has to be true. Here's a repeat of a diagram I drew earlier. -----y----------x-----FP-----x----------y----- 1/2WL dipole -----coil-----FP-----coil----- loaded dipole Assume the physical length of the loaded dipole is 1/4WL. Each coil replaces the section between 'x' and 'y'. The currents at 'x' and 'y' are quite different, being 1/8WL apart. Consider an 8 foot center-loaded 75m mobile antenna. 87% of the electrical length of the antenna is in 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! =----- |
Yuri Blanarovich wrote:
What I was looking for is to see 1. if anyone else MEASURED the current in loading coils, and what results they arrived at (and if we are wrong, then where did we go wrong). 2. If this is right than to have modeling software implement it with least error. I would like to use that for optimizing, say, loaded elements for receiving arrays on low bands, optimizing mobile antennas, loaded multielement beams, etc. Hi Yuri, try this out for your argument in the other group. Using EZNEC: Example 1: 102' CF dipole with loading coils in the center of each arm to cause the antenna to resonate on 3.76 MHz. I get XL=j335 ohms. Example 2: Replace the above loading coils with series inductive stubs hanging down. Ten foot stubs with six inch spacing between the wires is what I used. What happens to the current across that six inch gap is obvious from the current plot using EZNEC. Hint: There is a step function across that six inch gap just as there will be with a six inch coil. Then ask: Why doesn't EZNEC treat these two cases the same way? -- 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 Blanarovich wrote:
There is too much reliance now going on modeling program results, ignoring some realities. Yuri, here is a modeling result that you might like. :-) I took a 102' dipole and loaded it in the center of each leg with an inductive stub that made the dipole resonant on 3.76 MHz. I added a one ohm series 'load' to each side of the stub. Drawing one leg of the dipole, it looks like this: ----------R2-+ +-R1----------FP--- ... other half | | | | inductive | | stub +-+ EZNEC reports 0.85 amps through R1 and 0.57 amps through R2, a difference of 33%. If one could model the inductive loading reactance as an actual physical coil instead of a lumped single point impedance, results would be similar to the above. Now here is something that might blow some minds. The inductive stub above is ten feet long. That's about 1/8WL on 20m. A 1/8WL shorted stub equals +jZ0. The results of running the above antenna on 20m is that the current through R1 is 185 degrees out of phase with the current through R2. At the time when the current through R2 is flowing toward the end of the antenna, the current through R1 is flowing toward the feedpoint. Wonder what Kirchhoff would say about that. If you replace the stub with a coil of the same reactance, not much changes. Tell W8JI to stop using lumped circuit analysis when he should be using distributed circuit analysis. :-) -- 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! =----- |
Thank you Cecil and Fred!
(Where is Roy? We could use expert guidance in modeling the case.) I will post your comments on eHam.net. The analogy using stubs is excellent. That brings the question of using nice coils, vs. stubs, vs. toroids in shortened antennas. But we will save that for another thread with proper name. Now watch for W8JI twisting into: "I said that all along" see him changing his web page and become a guru who "discovered" that current accross the loading coil in the antenna is significantly different and Yuri (et al) will remain the idiot who can't get the things right :-).... Happened many times before :-( Thanks again! Yuri, K3BU/m As Ken, K7GCO keeps saying: "Don't they get tired of being wrong?" |
Yuri Blanarovich wrote:
Thank you Cecil and Fred! (Where is Roy? We could use expert guidance in modeling the case.) I sent Roy a copy of the EZNEC file that I sent to you. Anyone else who wants a copy of those files, send me an email. I will post your comments on eHam.net. Which forum/topic? -- 73, Cecil, W5DXP |
Cecil wrote,
Tell W8JI to stop using lumped circuit analysis when he should be using distributed circuit analysis. :-) -- 73, Cecil http://www.qsl.net/w5dxp You know, it's against the law to kill people, Cecil. I almost choked to death on my morning cup of Bo Lee when I read that. :-) 73, Tom Donaly, KA6RUH |
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Tdonaly wrote:
Cecil wrote, Tell W8JI to stop using lumped circuit analysis when he should be using distributed circuit analysis. :-) You know, it's against the law to kill people, Cecil. I almost choked to death on my morning cup of Bo Lee when I read that. :-) I apologize for that, Tom. If you had choked to death, would there have been enough evidence to convict me? :-) -- 73, Cecil, W5DXP |
Cecil wrote,
I apologize for that, Tom. If you had choked to death, would there have been enough evidence to convict me? :-) -- 73, Cecil, W5DXP Not in California, Cecil. It would have been the perfect crime. 73, Tom Donaly, KA6RUH |
"Mark Keith" wrote I beat Reg's vertload program to death finding the best overall coil height for my mobile antenna. Basically I ended up putting it as high as I could. Which ended up a center load at 5 ft up, with a 10 ft whip. =============================== There are 3 losses - coil loss resistance, ground loss resistance and radiation resistance. To calculate and maximise efficiency all 3 values must be transformed to a common point - the base feedpoint. The length of radiator between coil and base behaves is a transmission line transformer which transforms the coil loss resistance (XL/Q) to another value at the base. Would-be modellers should take this into account. The Cosine current distribution along the radiator is a direct consequence of its behaviour as a lossy line. (Actually, it is not an exact cosine shape because of end-effect) Efficiency = Rrad / ( Rrad+Rcoil+Rground ). Rground is constant. For short antennas Rrad is the smallest of the 3 resistances. As the coil is moved further up the antenna both Rrad and Rcoil increase. But even if the coil is located at the extreme top of the antenna, radiation resistance cannot increase to more than 4 times the radiation resistance when the coil is located at the base feedpoint. Usually it is considerably less than 4. So the rapidly increasing coil loss resistance very soon overtakes the increase in radiation resistance. Even if coil Q remains constant, coil loss resistance increases just by virtue of its necessary increase in inductive reactance. To maintain resonance coil inductance increases inversely proportional to the length of the whip above it. So when the coil is located 95% of the way to the top of the antenna its loss resistance is TWENTY times greater than that of a base loading coil even when Q is unchanged. In practice, a coil having 20 times the inductance but with the same overall dimensions will very likely have a lower Q and an even higher resistance. Its easy to see the fixed value of Rground in the above efficiency formula has the following effects - When coil loss is less than ground loss, higher radiating efficiency is achieved by placing the coil nearer to the top of the antenna. And vice-versa. When ground loss is very small (zero if antenna is a pair of two back-to-back radiators to form a dipole) efficiency is relatively high anyway, maximumum efficiency perhaps occurring with the coil located in the lower half of the antenna. The slight improvement relative to base loading (as part of a tuner) may not then be worth the mechanical inconvience of fitting a coil in the antenna anyway. An important factor, not considered quantitatively by anybody, is that a mobile antenna is not just a loaded vertical - the vehicle body, just by looking at it, obviously forms the major portion of the antenna and is floating above ground. The vehicle body plus loaded whip should be considered to be an off-centre-fed, short, 1/2-wave resonant vertical dipole and modelled as such. --------------------------------------------------------- Regarding antenna modelling - program LOADCOIL considers all 3 parts parts of the antenna, the mast, loading coil and whip, as consecutive lengths of transmission line each with its own Zo and loss resistance. It is obliged to do this because it covers actual antenna heights approaching 1/4-wavelength as may be erected in your backyard. And it continues to do this for very short antennas with very short loading coils even where there would be negligible error by assuming the current going into one end of the coil is the as what comes out of the other. There's a companion program TOPHAT2. There's no coil in it. ---- ======================= Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.g4fgq.com ======================= |
NM5K snip, snip and...
Besides, I've never really worried about it much. I don't think it would have any effect on how I build my short verticals. Good for you :-) Granted, we are close to optimum with mobile verticals. If I understand how and why things work, I can do better job on optimizing and maximizing the performance of the antennas, especially when it comes to more element loaded arrays. You would see significant difference in designing/optimizing say 3 element loaded beam. Modeling software uses currents in elements and calculates mutual interaction between the elements. If the current distribution and magnitude are off by 50% then we have major problem. Yuri |
I sent Roy a copy of the EZNEC file that I sent to you. Anyone else who wants a copy of those files, send me an email. I didn't get it, for direct mail take noSaddam out :-) I will post your comments on eHam.net. Which forum/topic? -- 73, Cecil, W5DXP The article and follow up comments are at: http://www.eham.net/articles/6512 Yuri, www.K3BU.us |
G4FGQ:
When ground loss is very small (zero if antenna is a pair of two back-to-back radiators to form a dipole) efficiency is relatively high anyway, maximumum efficiency perhaps occurring with the coil located in the lower half of the antenna. The slight improvement relative to base loading (as part of a tuner) may not then be worth the mechanical inconvience of fitting a coil in the antenna anyway. But not in the far field, affecting low angle radiation. Practical results and measurements show that it is worth the mechanical inconvinience to place the coils where they belong. Just ask Cecil about results of mobile antenna shootouts. An important factor, not considered quantitatively by anybody, is that a mobile antenna is not just a loaded vertical - the vehicle body, just by looking at it, obviously forms the major portion of the antenna and is floating above ground. At this time it is "bad" enough to look at this one aspect of loaded antennas. Of course in mobile antennas, the vehicle plays important role. W9UCW excluded that, used "perfect" radial field ground to eliminate other variables in order to have a closer look at the current distribution. Another interesting finding was that there was almost negligible difference in Q of coils. When they compared "perfect" loading coil (Bugcatcher type) with "poor" coil of Webster Bandspanner, thay saw fractions of dB difference. Yuri, K3BU/m |
Yuri Blanarovich wrote:
Practical results and measurements show that it is worth the mechanical inconvinience to place the coils where they belong. Just ask Cecil about results of mobile antenna shootouts. I feel the same way, Yuri, but at a shootout, +2dB is worth it's weight in tachyons. +2dB may or may not be noticeable during normal operation. I use a screwdriver even though I know how to do better. -- 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 Blanarovich wrote:
The article and follow up comments are at: http://www.eham.net/articles/6512 Egads, did I get the last word? (so far) That's proof of action at a distance. I'm a thorn in the side of hams who are not even on the same newsgroup as I. :-) -- 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 in message ...
Yuri Blanarovich wrote: The article and follow up comments are at: http://www.eham.net/articles/6512 Egads, did I get the last word? (so far) That's proof of action at a distance. I'm a thorn in the side of hams who are not even on the same newsgroup as I. :-) Dunno...I finally got up enuff courage to wade thru a bunch of that myself. Both had some decent points..But....Just using my built in "BS" filter only, which rarely seems to fails me, and ignoring all other influences, I still have to side with Tom. I still think the current is fairly constant. But not perfectly so, and can vary due to the antenna and it's mount, etc. I guess I'll just wait until the smoke clears to see how far off I am. This will be a good test of my filter unit. :) As far as who wins, I could care less. Nothing personal either way...But I have learned never to ignore my BS filter, so I'm going with it. :) MK |
But....Just using my built in
"BS" filter only, which rarely seems to fails me, and ignoring all other influences, I still have to side with Tom. I still think the current is fairly constant. Nothing personal either way...But I have learned never to ignore my BS filter, so I'm going with it. :) MK Same here, did your filter filtered out W5DXP pudding? The "theoretical" proof is right there. Or are you drinking the same coolaide as Tom? :-) Yuri Reality vs. Speculations? Duuuh? |
Mark Keith wrote:
Dunno...I finally got up enuff courage to wade thru a bunch of that myself. Both had some decent points..But....Just using my built in "BS" filter only, which rarely seems to fails me, and ignoring all other influences, I still have to side with Tom. I still think the current is fairly constant. The key to understanding is to realize that the net current is the phasor sum of the forward current and reflected current (on a standing- wave antenna). Assume a 10 degree phase delay through the coil on the frequency of operation. Ifwd-in and Iref-out are on the same side of the coil. Ifwd-out and Iref-out are on the other side of the coil. Ifwd-in-- coil Ifwd-out-- -----------------------////////////------------------------- --Iref-out --Iref-in Assume that |Ifwd-in| = |Ifwd-out| which satisfies Kirchhoff Assume that |Iref-in| = |Iref-out| which satisfies Kirchhoff Ifwd-in + Iref-out = net current on left side of the coil Ifwd-out + Iref-in = net current on right side of the coil Ifwd-out lags Ifwd-in by 10 degrees Iref-out lags Iref-in by 10 degrees (Iref-in leads Iref-out) Now let's assume that Ifwd-in and Iref-out are in phase. So current on the left side of the coil equals Ifwd-in at zero degrees plus Iref-out at zero degrees which is a current maximum point. Ask yourself: Can we have a current maximum point on both sides of the coil? I trust that answer is obvious. Ifwd-out lags Ifwd-in by 10 degrees. Iref-in leads Iref-out by 10 degrees. So current on the right side of the coil equals Ifwd-out at -10 degrees plus Iref-in at +10 degrees, NOT a current maximum point. Therefore, in this example, net current on the left side of the coil cannot possibly be equal to net current on the right side of 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! =----- |
Yuri Blanarovich wrote:
Same here, did your filter filtered out W5DXP pudding? The "theoretical" proof is right there. Or are you drinking the same coolaide as Tom? :-) Yuri, my latest posting sheds more light. Apparently, W8JI doesn't realize that there are two superposing currents phasor-adding together to get the net current and the phase distribution between those two current waves are opposite because they are traveling in opposite directions. This is a characteristic of standing-wave antennas. See what happens when one tries to ignore the component waves? Because the two currents are traveling in opposite directions, any phase delay through the coil shifts the phase of the two currents IN OPPOSITE DIRECTIONS. Thus the total relative phase shift effect through a 10 degree coil is 20 degrees. -- 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! =----- |
Therefore, in this example, net current on the left side of the coil cannot possibly be equal to net current on the right side of the coil. -- 73, Cecil http://www.qsl.net/w5dxp Thanks for another gem, I apologize to Reflected Waves, for they are important and I will treat them with greater respect. I still don't like them in the feedlines, but I love them in the radiators :-) Yuri, www.K3BU.us |
Yuri Blanarovich wrote:
I apologize to Reflected Waves, for they are important and I will treat them with greater respect. I still don't like them in the feedlines, but I love them in the radiators :-) Yuri, to be perfectly consistent, you would need to change all your standing-wave antennas to traveling-wave antennas. I've got some non-inductive terminating resistors for sale at the right price. :-) -- 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, to be perfectly consistent, you would need to change all your standing-wave antennas to traveling-wave antennas. I've got some non-inductive terminating resistors for sale at the right price. :-) -- 73, Cecil http://www.qsl.net/w5dxp Well, I've been thinking on those sleepless nights, how to turn standing wave Yagis or Quads into traveling wave ones, with no back lobes. Got recipe? I've got resistors. Yuri |
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Radio amateurs and just as many professionals suffer from delusions of
accuracy where RF measurements are concerned. Especially HF current and power measurememts. Far too much importance is attached to names like GR and HP and Fluke rather than their own abilitity to assess and sum the accumulation of measuring errors. -- ======================= Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.g4fgq.com ======================= "Mark Keith" wrote in message om... oSaddam (Yuri Blanarovich) wrote in message ... But....Just using my built in "BS" filter only, which rarely seems to fails me, and ignoring all other influences, I still have to side with Tom. I still think the current is fairly constant. Nothing personal either way...But I have learned never to ignore my BS filter, so I'm going with it. :) MK Same here, did your filter filtered out W5DXP pudding? The "theoretical" proof is right there. Or are you drinking the same coolaide as Tom? :-) Yuri Reality vs. Speculations? Duuuh?'' Oh, purely speculation on my part. I have no easy way of really knowing the reality. There is a small part that keeps bugging me, but I'd have to see for sure where he is measuring the currents. I missed the pix on the site. I'll assume for now he measured at each end of the coil, pretty much at the connection to the mast or whip. The part the bugs me is a possible stunting of the current at the top of the coil due to the capacitance it is looking at, at the end of the coil. To my thinking, once you leave the coil, even right at the end, you should see a reduction of current, compared to say even a turn or two from the top of the coil. I'm just wondering if this may be giving a false indication of the true currents within the coil,if he is measuring slightly outside of the coil. I'd be more satisfied if he could measure a few turns from each end "using a large, many turns, coil for 80 or 160" to get a general view within the windings themselves. But I realize this could be very difficult. You all may be totally correct. I'd just like to be a little better convinced before I totally agree. I expect a slight decrease in current at the top vs bottom. But I don't expect it to be large. I also don't expect the bottom of the coil to be "hot", with a radical current taper on the upper windings. The main thing I see to causing a reduction of current , is the stinger on top of the coil. "capacitance" I wonder if he is seeing the effects of that capacitance in his lower measurement? Only the shadow knows for sure....:/ As far as the reverse currents Cecil mentions, I'd have to ponder that a while. Seems to me that could wildly vary from antenna to antenna depending on height, coil positions, any top loading, etc..Although it looks good on paper, I smell a hook. So I'd have to think about that more. BTW, this amount of current in the coil, is something I've also thought about myself. I've just come to the "different" conclusion it's fairly constant through the coil. I could always be wrong. Wouldn't be the first time.. But I need to see/hear a bit more to be convinced. MK |
Mark Keith wrote:
As far as the reverse currents Cecil mentions, I'd have to ponder that a while. While you are pondering, here is a quote from _Antenna_Theory_, by Balanis. "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents 'If' and 'Ib' in Figure 10.1(a)." Standing wave antennas necessarily have standing waves caused by forward waves and reflected waves. Analyze any coil subjected to forward current and reflected current and you will be forced to agree that the current at one end of the coil is not the same as the current at the other end of the coil. W8JI is thinking lumped circuits when he should be thinking distributed networks. The phase shift through the coil changes the phase relationship between the forward current and reflected current, so of course, their superposed value will be different at each end of 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! =----- |
Reg finally figured it out:
Radio amateurs and just as many professionals suffer from delusions of accuracy where RF measurements are concerned. Especially HF current and power measurememts. Far too much importance is attached to names like GR and HP and Fluke rather than their own abilitity to assess and sum the accumulation of measuring errors. Thank goodness we have your formulas, failproof programs and variety of speculations. Gentlemen, case is solved, closed. We can't measure it, we are all bunch of dumb delusional morons with faulty instruments who don't know how to use them. Current must be the same in the coil according to Rauch, Kirchoff, Ohm, Reg. So now make your antennas out of coils, you will have constant current radiator tip to tip with 300% efficiency and you can throw your instruments away. Reg has the formula for it, use it! Seriously, I thank you Cecil, Fred and few others who enlightened our case, that's what I was hoping for and found it here. It will be the springboard for further development, it already gave me some ideas how to improve efficiency of loaded aerials. The others from the flat earth society showed their colors and they ain't pretty. Just like democRATs, when they are deficient in arguments they triviliarize and ridicule. We are planning mobile antenna shootout here on east coast in the spring, so get your wares ready and see who is da king koil. Yuri, da BU/m |
I once had an occasion where the bottom of a coil did get warm, while the top did not. Yet my RF ammeters showed the same current on both ends. What was going on? What was he measuring, where was the coil? W9UCW used 100 mA at the bottom, I doubt that this would "cook" the coil. You see the pictures, they are good quality coils and he use two meters and flippped the coil to eliminate possible error as described here. I ultimately determined that the soldered connection from the coil to the lower antenna mast (for experimentation, it was copper) was adding some undesireable resistance. Solder is not a particularly good conductor of electricity. I copper-plated over the solder joint. Not only did the bottom section of the coil no longer get warm, but the two RF ammeters both showed about 20% more current flowing in the antenna. And my far-field instruments showed a 1.5dB increase in field strength. Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No meters, no hokus pokus, just "naked" antenna. This is one example of being fooled....If you took coil temp at face value, you would think the current taper was quite steep, judging from the temp's of the windings. But nope...A resistive connection seemed to be the culprit. Note that his meters showed the same current on both ends. :/ You can see why I'm afraid of that "hook" that usually is lurking ready to bite at a moments notice. Don't worry, if you are right, it will come out in the end. But that hook...Ouch.. MK One insufficiently described measurement is enough to throw rest out of the window? W9UCW has shown data from various measurements and positions of the coil (pictures how it was done) and W5DXP backed it up with explanation of reflected wave and simulation and comparison with loading stub. It came out, this is the ned. If you choose not to believe, its a free country :-) Yuri |
More pudding!
I added picture of current distribution when using inductance in the form of loading stub as described earlier and from Eznec file supplied by Cecil. It is at the end of the article at http://www.k3bu.us/loadingcoils.htm It shows the jump accross the stub, but when replaced by lumped inductor, the Eznec shows constant current accross the coil. Yuri |
Yuri Blanarovich wrote:
Current must be the same in the coil according to Rauch, Kirchoff, Ohm, Reg. Kirchhoff and Ohm were not wrong. For a lossless coil, the forward current magnitude must be the same in the coil and the reflected current magnitude must be the same in the coil. But the net current is the sum of those two component waves which have phase angles rotating in opposite directions. The basic problem is using lumped circuit calculations for a distributed network problem, a well known no-no. -- 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 haven't had the time to participate in this, but in a brief look, it
looks pretty silly. Of course EZNEC shows no current difference across a load. The EZNEC model of a load has zero length, so the current at both terminals has to be the same. You will see a current change over the length of a model of a conductor, because it does have length. The coil in the web site pictures certainly has length, so why should you be surprised to find a current change over its length? Did the experimenter perhaps do the same test with the meters placed the same distance apart with just a conductor in between? Would there be some great revelation in finding that the current was different at the two points? I was intrigued by the claim that a toroid measured significantly different from one end to the other. I wonder if the tester tried reversing the meters to verify that he got the same reading in both cases. If he did, I'd be interested in learning more details. Unfortunately, the main objective of the web site seems to be to insult Tom, W8JI, rather than to be objective. So in my mind that leaves the possibility open that the experimenter is more interested in finding evidence that would disprove Tom than in presenting carefully measured and objective data. Roy Lewallen, W7EL Yuri Blanarovich wrote: More pudding! I added picture of current distribution when using inductance in the form of loading stub as described earlier and from Eznec file supplied by Cecil. It is at the end of the article at http://www.k3bu.us/loadingcoils.htm It shows the jump accross the stub, but when replaced by lumped inductor, the Eznec shows constant current accross the coil. Yuri |
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