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You claim to be a science minded person, yet you choose to accept theoretical results over contradicting empirical data, and do so, without even an iota of curiosity. That is not science, it's closed-minded silliness! Equally as silly, is your raising such a stink over 1/3 of a dB... which will prove to be your Waterloo. :) 73, Chuck, WA7RAI I'l second that! Very precisely put :-) Yuri |
Roy Lewallen wrote in message ... Sorry, Chuck, I can't thing of one reason why I should accommodate you. Gee, Roy... does this mean you don't want me to know your reply to my acceptance of your challenge? Having second thoughts about this, perhaps? In any event, there's always Google... aside from that, some good person here will post it, I'm sure. Does this also mean that you cannot back up your bi-directional claims with facts? A pity... Chuck, WA7RAI Roy Lewallen, W7EL Chuck wrote: Roy, Linear, yes... bi-directional? Not as I see it... and leaves one wondering why NEC3 is available only to government entities and contractors... To confirm your claim, please post a demonstration that confirms energy in the load is flowing into the input. Also, please repost your reply to my post with the header "another lie..." as it did not show up in my newsreader. Thanks, Chuck, WA7RAI |
Ian, if I ever understood, I have long ago lost track of the raging arguments and consequences. You are quite correct, of course, in your analysis of what goes on in and around a loading coil. But in the face of such rigid minds and attitudes your attempts to convince people of the errors in their ways by simple logic is doomed to failure. A solenoidal coil of wire, a loading coil of any proprtions, can be considered to be a continuously loaded, fat, relatively short, single wire, transmission line. Because of the inductive loading it will have a much higher Zo than a solid cylinder of the same length and diameter. Its inductance per unit length will be that of the coil. Its capacitance per unit length will be largely unchanged. For close-wound turns tt will be the same as the solid cylinder. For spaced turns capacitance will only be slightly reduced and calculable. Zo = Sqrt(L/C) and R is the wire HF resistance including proximity effect. To simplify, for a first approximation R can be neglected and the line becomes loss-less. If the length of coil is long enough then its radiation resistance Rrad may be high enough to be taken into account alongside R. The propagation velocity V = 1/Sqrt(L*C) from which phase-shift per unit length of coil can be calculated. (Phase shift appears to be a sore point in the arguments) If necessary, attenuation per unit length can be calculated from R+Rrad. The properties of this line, the coil, is now amenable to normal transmission line analysis with a fair degree of accuracy. Accuracy is limited by the accuracy of determining coil dimensions. Such things as the increase in overall diameter by wire diameter matter. Input impedance can be calculated from the terminating impedance. The terminating impedance is the remainder of the antenna (another transmission line) but for the purpose of settling arguments arbitrary values can be chosen. The phase shifts relative to feedpoint at each junction along the loaded antenna can be calculated. Some of my programs use the above-described calculating method. But none of them have relative-phase outputs for the simple reason that nobody has yet found any practical use for such useless data and in any case there's usually not enough space on the screen. All phases are relative. I've a feeling arguments have arisen because of confusion about what phases are relative to. You've been arguing about different things and you can't ALL be that stupid. Unfortunately, communication via newsgroups cannot make use of body-language. ;o) ;o) ---- Reg, G4FGQ |
I wouldn't bother responding, but I'm afraid some readers might be
misled by what's being said here. Chuck wrote: Yes Roy, It has been well established that the available NEC engines model extremely well with conventional designs. That is not the issue. Your innuendo regarding 'professional' customers is silly. In my 67 years, have been Chief Engineer of commercial radio and television stations, as well as having designed commercial radio and television stations, including the first all solar powered commercial (5 KW) FM station in the US. You seem to opine that the ability to make measurement's is limited to a only special few. Since none of your customers are producing critically coupled designs, your arguments in this regard are without merit, and IMO, the intent of this post was a failed attempt to reduce my standing. The statement about professional users wasn't meant to be innuendo or any sort of slight, but simple fact. I was referring to the aerospace companies, government agencies, universities, broadcast consultants, international broadcast companies, space agencies, and the like that routinely use EZNEC, and some of whom continue to buy additional copies of the professional versions. (Surely you regard these as professional users?) And they don't tell me (or hardly anyone else) specifically the kinds of antenna they design. Since your antenna is seemingly the only one which is incapable of being modeled (other than ones which can't be modeled for well known and documented reasons), you alone must have the key to the magic involved. The NEC-2 manual is available from the web. It explains in detail how the network model, which is used for transmission lines, is implemented. Surely someone with your extensive professional background is able to read and understand it. You claim to be a science minded person, yet you choose to accept theoretical results over contradicting empirical data, and do so, without even an iota of curiosity. Ah, here we go again. Someone makes claims that contradict known and widely accepted principles. Then the charge is made that anyone who disbelieves is narrow minded and without curiosity, and challenged to disprove the extraordinary assertions. I have no obligation to once more show the validity of accepted science; the evidence is there in abundance for anyone with curiosity to see. It's up to you to back up your extraordinary claims with evidence. All I've seen from you for evidence is a mention of back-yard measurements. This is hardly enough to convince me or any rational person that established physics is wrong. I've even put my money where my mouth is, and offered to pay for a real, objective test of your antenna. That's all you're going to get. That is not science, it's closed-minded silliness! Equally as silly, is your raising such a stink over 1/3 of a dB... which will prove to be your Waterloo. :) And that isn't even worthy of a response. Roy Lewallen, W7EL |
Chuck wrote:
Linear, yes... bi-directional? Not as I see it... and leaves one wondering why NEC3 is available only to government entities and contractors... . . . It's not clear why you have a problem with NEC-3 when it was superceded long ago by more-advanced NEC-4. NEC-4 can be purchased by nearly anyone, as a little web research would have quickly revealed. Yes, even you can buy NEC-4. But alas, it also doesn't take into account magical phenomena. Roy Lewallen, W7EL |
Ian,
The equivalent shunt self-capacitance of a coil obviously affects the magnitude and phase of the current which flows in it. This particularly applies when a high-value loading coil is near to the top of a vertical antenna which is terminated with a very short rod or whip. (The self-capacitance of an isolated coil is calculable and can be easily checked by using one of these small hand-held antenna analysers to measure a coil's self-resonant frequency extremely accurately.) In the extreme case, when there is no whip, the only capacitance across the coil is its own self-capacitance. Yet to behave as a loading coil and draw current up the antenna below it, it is required to have a low impedance. A circuit analysis becomes quite involved. The coil impedance has to be in the form of a series resonance with the length of antenna wire below it. So we have a series resonance in the presence of the coil's shunt capacitance. From ordinary lumped circuit theory the equivalent coil Q drastically falls, a very large voltage appears across the coil, and a very large circulating current flows around the coil and its own self-capacitance. Efficiency goes for a Burton and with a high power transmitter either the coil melts or collapses due to voltage-breakdown between turns. The moral of this story is never to locate a loading coil near the top of an antenna. It also explains why maximum efficiency usually occurs between half-way and 2/3 of the way up. With an exceptionally good ground maximum efficiency occurs with bottom loading. In which case you don't need a coil in the antenna at all. You can include it in the tuner. To see how radiating efficiency of a short or long vertical changes with coil height and how coil loss increases extremely rapidly as the coil nears the top of the antenna, download in a few seconds program LOADCOIL from website below. Its quite safe to use the program - there's no danger of setting the coil on fire. You can slide the coil up and down the antenna from the keyboard and immediately observe how a variety of parameters change. Also copious notes. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Ian White, G3SEK wrote:
"Step 1: I am starting from the fundamental AC current behaviour of an ideal inductor." Good start, but incomplete. Fundamental a-c does not include a standing-wave wehich causes a variation of voltage, current, and impedance along the length of the inductor whether straight or coiled. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
Ian White, G3SEK wrote: "Step 1: I am starting from the fundamental AC current behaviour of an ideal inductor." Good start, but incomplete. Fundamental a-c does not include a standing-wave wehich causes a variation of voltage, current, and impedance along the length of the inductor whether straight or coiled. I was going to get back to you about that (but Life intervened), to say that I agree with your entire analysis of standing waves on antennas... except for that one point. We need to be very clear about the difference between an ideal inductor and any practical inductor. An ideal inductor has only one property: inductance. It does not have length, diameter, self-capacitance, parasitic capacitance or any of the extra properties that a practical coil has. Let's ignore those for the moment, and try to understand how an antenna is loaded by pure inductance alone. The behaviour of loading inductANCE does not not involve any variation in current between one terminal of the inductance and the other. It cannot, because that is not one of the properties of inductance - not ever, in any circumstances. With a pure loading inductance, the current profile on the antenna has to fit the constraint that the current immediately above the inductance must be equal to the current immediately below it. In the real-life case this is not necessarily true - but we need to be absolutely clear that any difference in current between the top and bottom of a practical loading coil has to be due to those "extra" properties mentioned above. It is not due to the inductance alone, because inductance alone doesn't do that. Unless we understand this fundamental point about how an antenna is loaded by pure inductance, we have no hope of understanding how real-life loading coils actually behave. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Ian White, G3SEK wrote:
"The behaviour of loading inductANCE does not involve any variation in current between one terminal of the inductance and the other." Yuri has attached a photo in this thread again of an antenna loading coil in action as a psrt of a too-short vertical antenna. RF ammeters are mounted in series, one at the coil top and one at the coil bottom. The lower ammeter clearly shows more current than the upper. That`s exactly as should be expected. The too-short whip above the coil has an impedance consisting of a high capacitive reactance and a few ohms of radiation resistance. It`s the coil`s job to cancel the capacitive reactance so it doesn`t oppose current into the too-short whip. Pure inductance alone can cancel pure capacitive reaxctance. In an antenna loading coil as used in a "Texas Bug Catcher", the coil resides about in the middle of the antenna. The coil has length and current, the two factors which produce radiation. The Bug Catcher is approximately a 90-degree antenna, including the phase delay in the loading coil/. ON4UN shows in Fig 9-22 on page 9-15 of "Low=Band DXing", a center-loading example which may represent the Bug Catcher The current taper shown by ON4UN is similar to that shown by other authors deliberately and unmistakenly. A pure series inductance invokes a phase lag. This would be 90-degrees in a pure inductance but we always have some resistance which reduces the phase lag to less than 90-degrees. In olden times, chokes were often called "retard coils". Best regards, Richard Harrison, KB5WZI |
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