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Yagi antenna design question
I wonder whether anyone can formulate a convincing answer to the following
question. Let us assume you wish to design a 3-element Yagi antenna for good performances, but with NO REGARD AT ALL TO ITS IMPEDANCE (i.e. assume that you anyway intend to have a matchbox at the antenna terminals, so that the antenna impedance is of no concern at all for you). At this point you run a good antenna design program, giving it no constrain in terms of antenna impedance. The program will give you the "optimal" solution in terms of element length and spacing, typically also showing the antenna impedance at the feedpoint, that we here assume to be e.g. 30 ohm. At this point you change your mind and, instead of using a 30-to-50 ohm matchbox, you decide to match the antenna to the cable using the well known hairpin technique, by which the radiator length is reduced somewhat (to create some capacitive reactance in series with the antenna resistance) and an inductor is put in parallel to the antenna (to resonate the residual capacitance after resistance transformation). Doing so the radiator length will result to be shorter that the length calculated by the computer program, and one could then presume that the actual antenna radiation characteristics (gain & front-to-back performance, radiation pattern) do not correspond to those calculated by the program any longer. Even though the changes may be small, I would anyway be interested to understand whether, in principle, the hairpin technique results in a change of the antenna radiation characteristics. If the change is confirmed, we would inevitably also come to the conclusion that the antenna radiation characteristics depend on the technique which is adopted to match the antenna to the cable (e.g. matchbox or hairpin). This would sound real odd! Thanks and 73 Tony I0JX |
Yagi antenna design question
On Sun, 4 Feb 2007 15:39:49 +0100, "Antonio Vernucci"
wrote: I wonder whether anyone can formulate a convincing answer to the following question. Let us assume you wish to design a 3-element Yagi antenna for good performances, but with NO REGARD AT ALL TO ITS IMPEDANCE (i.e. assume that you anyway intend to have a matchbox at the antenna terminals, so that the antenna impedance is of no concern at all for you). Hi Tony, That is a good start for discussion, but you abandon this care-free attitude almost immediately: ...that we here assume to be e.g. 30 ohm. Chances are it will be much less, possibly 5 Ohms. So, you see, you have already introduced a constraint, and you continue adding mo At this point you change your mind and, instead of using a 30-to-50 ohm matchbox, you decide to match the antenna to the cable using the well known hairpin technique, ... Which leads to another constraint: Doing so the radiator length will result to be shorter ... As you are using a modeler from the beginning, you should also use these constraints from the beginning. Perhaps you are thinking of this as a two step process starting with no constraints and then adding them. That works too and it requires you to perform successive refinement. You can not escape this anyway. If the change is confirmed, we would inevitably also come to the conclusion that the antenna radiation characteristics depend on the technique which is adopted to match the antenna to the cable (e.g. matchbox or hairpin). This would sound real odd! The change could be small. The question is how much change makes it a "real odd" result? 73's Richard Clark, KB7QHC |
Yagi antenna design question
"Antonio Vernucci" wrote in message ... I wonder whether anyone can formulate a convincing answer to the following question. Let us assume you wish to design a 3-element Yagi antenna for good performances, but with NO REGARD AT ALL TO ITS IMPEDANCE (i.e. assume that you anyway intend to have a matchbox at the antenna terminals, so that the antenna impedance is of no concern at all for you). At this point you run a good antenna design program, giving it no constrain in terms of antenna impedance. The program will give you the "optimal" solution in terms of element length and spacing, typically also showing the antenna impedance at the feedpoint, that we here assume to be e.g. 30 ohm. At this point you change your mind and, instead of using a 30-to-50 ohm matchbox, you decide to match the antenna to the cable using the well known hairpin technique, by which the radiator length is reduced somewhat (to create some capacitive reactance in series with the antenna resistance) and an inductor is put in parallel to the antenna (to resonate the residual capacitance after resistance transformation). Doing so the radiator length will result to be shorter that the length calculated by the computer program, and one could then presume that the actual antenna radiation characteristics (gain & front-to-back performance, radiation pattern) do not correspond to those calculated by the program any longer. Even though the changes may be small, I would anyway be interested to understand whether, in principle, the hairpin technique results in a change of the antenna radiation characteristics. If the change is confirmed, we would inevitably also come to the conclusion that the antenna radiation characteristics depend on the technique which is adopted to match the antenna to the cable (e.g. matchbox or hairpin). This would sound real odd! Thanks and 73 Tony I0JX Tony, by using hairpin matching, you take out portion of the highest current on the element and fold it into the hairpin where it is taken out of antenna "participation" for the price of match. Better solution is to feed the element off center (K7GCO idea), find the 50 ohm point, insert the insulator and feed it with balun. This way you preserve the full size of the driven element and its coupling to parasites and higher antenna efficiency. Better way is to use quad elements where the stacked elements, higher impedance and full size elements produce most gain per boom length (up to 5 elements) 73 Yuri, K3BU |
Yagi antenna design question
On Feb 4, 2:35 pm, "Yuri Blanarovich" wrote:
[snip] Tony, by using hairpin matching, you take out portion of the highest current on the element and fold it into the hairpin where it is taken out of antenna "participation" for the price of match. You're kidding right? Disclosu I use a hairpin (beta) match on my HB Yagi. |
Yagi antenna design question
"Wes" wrote in message ups.com... On Feb 4, 2:35 pm, "Yuri Blanarovich" wrote: [snip] Tony, by using hairpin matching, you take out portion of the highest current on the element and fold it into the hairpin where it is taken out of antenna "participation" for the price of match. You're kidding right? Disclosu I use a hairpin (beta) match on my HB Yagi. In that case I must be :-) Can you elaborate why would I be kidding? As far as I know: If you use hair pin inserted in the middle of the element, you get the shorter physical length of the element - smaller high current carrying length. Half wave resonant element has maximum current in the center, by folding portion of that element into a hair pin we take that portion "out of the picture". Just like a loading coil at the base of the vertical - current drop along the coil. Hairpin is usually folded back on the boom, 90 deg. to radiator, with any current left, not participating in the plane of the elements. Hairpin loading stubs were proven to be worse loading elements than good quality coils. You would be better off by inserting coil at the feedpoint instead of (Beta match) hairpin, or use Delta match, or offset feeding at the 50 ohm pointas mentioned before. We might be splitting hairs here, but I hate to lose even fraction of dB if there is a better way. I know Beta match works, I used it in some antennas (don't like Gamma matches), even made a QSO with a ligthbulb as an antenna. It's all relative. Contesters like to chase every fraction of a dB lost, soon they can add up to some noticeable real dBs. YMMV 73 Yuri, K3BU |
Yagi antenna design question
On Feb 5, 7:59 am, "Yuri Blanarovich" wrote:
"Wes" wrote in message ups.com... On Feb 4, 2:35 pm, "Yuri Blanarovich" wrote: [snip] Tony, by using hairpin matching, you take out portion of the highest current on the element and fold it into the hairpin where it is taken out of antenna "participation" for the price of match. You're kidding right? Disclosu I use a hairpin (beta) match on my HB Yagi. In that case I must be :-) Can you elaborate why would I be kidding? As far as I know: If you use hair pin inserted in the middle of the element, you get the shorter physical length of the element - smaller high current carrying length. I believe that your first problem is that you are considering the hairpin (Beta) to be part of the radiator instead of considering the actual case; it's part of the matching network. Half wave resonant element has maximum current in the center, by folding portion of that element into a hair pin we take that portion "out of the picture". Just like a loading coil at the base of the vertical - current drop along the coil. op cit. I'm not "folding a portion of the element." If you subscribe to the idea that part of the antenna can be "folded into" the feeder and that by selecting the right feeder length you can "lengthen the antenna" (as shown in a lot of old ARRL literature) then I have a new limited space antenna for you. It's a one foot long radiator with a variable length feeder (a la Cecil) that "makes up" the missing antenna length. Hairpin is usually folded back on the boom, 90 deg. to radiator, with any current left, not participating in the plane of the elements. If I placed a discrete (lumped element) L-network at the feedpoint the current in it would not be "participating" either. Hairpin loading stubs were proven to be worse loading elements than good quality coils. When, where, by whom, etc? Oh, BTW, did I mention "THE HAIRPIN IS NOT A LOADING ELEMENT. It's the inductance in an LC L-network. You would be better off by inserting coil at the feedpoint instead of (Beta match) hairpin, or use Delta match, or offset feeding at the 50 ohm pointas mentioned before. Why? The hairpin will handle all the power an amateur can supply, it can (does in my case) form an integral balun and it DC grounds the element. We might be splitting hairs here, but I hate to lose even fraction of dB if there is a better way. No gain is lost. I can model my Yagi with and without the Beta, resonating the antenna without it by lengthening the element and the gain remains the same within 0.01 dB. I know Beta match works, I used it in some antennas (don't like Gamma matches), even made a QSO with a ligthbulb as an antenna. It's all relative. Contesters like to chase every fraction of a dB lost, soon they can add up to some noticeable real dBs. I've been a moonbouncer, I know all about fractions of a dB. |
Yagi antenna design question
"Wes" wrote in message oups.com... On Feb 5, 7:59 am, "Yuri Blanarovich" wrote: "Wes" wrote in message ups.com... On Feb 4, 2:35 pm, "Yuri Blanarovich" wrote: [snip] Tony, by using hairpin matching, you take out portion of the highest current on the element and fold it into the hairpin where it is taken out of antenna "participation" for the price of match. You're kidding right? Disclosu I use a hairpin (beta) match on my HB Yagi. In that case I must be :-) Can you elaborate why would I be kidding? As far as I know: If you use hair pin inserted in the middle of the element, you get the shorter physical length of the element - smaller high current carrying length. I believe that your first problem is that you are considering the hairpin (Beta) to be part of the radiator instead of considering the actual case; it's part of the matching network. Do you have to shorten the (driven) element if you insert the hairpin in the middle or not (to maintain the resonant frequency)? Telrex 40m Yagis did use hairpins at the center of the element as a loading and shortening the element length. To me that is the matching network too, but at the expenses of shortening the element length - center loading, similar to base loading the resonant quarter wave vertical. Half wave resonant element has maximum current in the center, by folding portion of that element into a hair pin we take that portion "out of the picture". Just like a loading coil at the base of the vertical - current drop along the coil. op cit. I'm not "folding a portion of the element." If you subscribe to the idea that part of the antenna can be "folded into" the feeder and that by selecting the right feeder length you can "lengthen the antenna" (as shown in a lot of old ARRL literature) then I have a new limited space antenna for you. It's a one foot long radiator with a variable length feeder (a la Cecil) that "makes up" the missing antenna length. You fold the portion of the element, it's called loading, at the base, in the middle or anywhere along the element length. The folded hairpin has inductance, just like a coil, and can be replaced with the coil of similar inductance. The loading element is not the limited space antenna, look at the currents at its ends and see the difference in curent distribution along it and how it participates in the overall radiator current distribution and corresponding area under the cosine curve representative of the efficiency. We are back to the loading coil "problem" and that's why we pointed out the efect and its impact on the antenna performance. Hairpin is usually folded back on the boom, 90 deg. to radiator, with any current left, not participating in the plane of the elements. If I placed a discrete (lumped element) L-network at the feedpoint the current in it would not be "participating" either. Not much, but help with cleaner pattern. Hairpin loading stubs were proven to be worse loading elements than good quality coils. When, where, by whom, etc? Oh, BTW, did I mention "THE HAIRPIN IS NOT A LOADING ELEMENT. It's the inductance in an LC L-network. Here we go again? We are talking about standing wave circuit - antenna radiator or element. So inductance is not a loading element? As far as I know inductance (coil, hairpin) or capacitance (top hat, L, T loading) are used as a loading elements to shorten the physical length of the antenna element, while maintaining electrical length. There was an article by W6?? in CQ and other examples when they replaced hairpin loading on Yagi elements with coils and got significant improvement in the performance of KLM 3 el 80 Yagi, better gain, much better pattern due to less interference of the folded back hairpin with the element. Measurements and modeling before and after showed that. pointas mentioned before. Why? The hairpin will handle all the power an amateur can supply, it can (does in my case) form an integral balun and it DC grounds the element. No argument here, you can do that with coil and gain some edge. We might be splitting hairs here, but I hate to lose even fraction of dB if there is a better way. No gain is lost. I can model my Yagi with and without the Beta, resonating the antenna without it by lengthening the element and the gain remains the same within 0.01 dB. No gain lost would be 0.0000 dB :-) I know Beta match works, I used it in some antennas (don't like Gamma matches), even made a QSO with a ligthbulb as an antenna. It's all relative. Contesters like to chase every fraction of a dB lost, soon they can add up to some noticeable real dBs. I've been a moonbouncer, I know all about fractions of a dB. Then you should appreciate the above. 73 Yuri, K3BU |
Yagi antenna design question
Wes wrote:
op cit. I'm not "folding a portion of the element." If you subscribe to the idea that part of the antenna can be "folded into" the feeder and that by selecting the right feeder length you can "lengthen the antenna" (as shown in a lot of old ARRL literature) then I have a new limited space antenna for you. It's a one foot long radiator with a variable length feeder (a la Cecil) that "makes up" the missing antenna length. Why didn't I think of that? The SWR on the ladder line on 40m would only be 47,000,000:1 and the feedpoint impedance would be 10 micro-ohms at system resonance. -- 73, Cecil http://www.w5dxp.com |
Yagi antenna design question
This will be the last word I have on this topic.
I have placed two files he www.k6mhe.com/n7ws/N7WS_Yagi_Resonant.EZ and he www.k6mhe.com/n7ws/N7WS_Yagi_Shortened.EZ The files are models of my 20-meter three-element Yagi that are as nearly representative of the physical antenna and its location as I can make them. The only difference between them is the half-length of the DE. The actual antenna uses the shortened version with a stub (Beta) matching/balun arrangement. Two photos of the details of this are he www.k6mhe.com/n7ws/YagiFeed-1a.jpg and he www.k6mhe.com/n7ws/YagiFeed-2a.jpg The photos were taken with the antenna mounted on the tower and the tower folded over in case you're wondering about the orientation. For the purposes of the discussion I have removed the stub matching system from the model. The following transformation and matching exercise can be performed using a Smith Chart, your favorite computer program or with pencil on the back of an envelope. I happen to prefer, and highly recommend, AC6LA's XLZIZL.xls Excel workbook for this stuff. First let's analyze the full-length, resonant DE version. After running the analysis we (should) have a feedpoint Z of 26.76 +j0 and a gain at the selected elevation of 12.91 dBi. The SWR is 1.87:1. Instead of the integral stub, which Yuri believes is part of the antenna that is "folded back" along the boom, I will move the matching system away from this location using an ideal ½ wavelength (34.7 foot) transmission line with an ideal current balun at the antenna end. I don't believe anyone would argue that the feedpoint impedance is not replicated exactly at the input end of this line. At the input end of the lossless line, the Z is of course, 26.76 +j0. Because, as will be shown, the stub matching system is nothing more than an L-network; I will use the same at the input of the half- wavelength line. I begin by inserting a series capacitor, C = 448 pF and Q = 1000. At the input side of this capacitor the Z is now: 26.785 -j25.062. If using XLZIZL, the loss in this capacitor is shown as 0.004 dB, because Q is not infinite. Continuing, I place a shunt inductor, L = 0.6, Q = 200 across the input of the series capacitor. The resulting input Z = 50.00 +j0.2. The total network loss is 0.02 dB. This is the baseline. Returning to the shortened driven element version, after analysis, we find that the input Z = 24.55 -j25.2 and the gain is unchanged at 12.91 dBi. At the input end of our magical ½ wavelength line, the Z remains 24.55 -j25.2. Once again using the L-network system, I find that the series capacitor is unnecessary and I can proceed by adding a shunt inductance. Rather than using Yuri's "preferred" discrete inductor, let's use a "lossy" stub. Instead of using the large diameter, parallel tube stub of the actual antenna, I'll use a standard transmission line for the stub. XLZIZL has a number if transmission lines and their parameters "built in," including the Wireman ladder lines. The parameters for these are those I derived in my ladder line paper. http://www.k6mhe.com/n7ws/Ladder_Line.pdf Selecting Wireman 553, shorting one end and placing the other in parallel with the input to the lossless line and doing a little manipulation and I find that a 14.85" length makes the Z = 50.12 +j0.18. The network loss remains 0.02 dB. So much for this less than ideal stub vs. Yuri's preferred discrete inductor. There you have it. The stub matching method is equal to a discrete L- network in efficiency, it does not detract from the antenna efficiency one bit, it can incorporate the balun function without additional components, it grounds the feedpoint, with a little sealant on the cable, it is weatherproof and unlike Gammas and Tee-matches, it will handle full power without being prone to capacitor breakdown. It is not part of the radiator; it is part of the matching network. Period. |
Yagi antenna design question
Wes wrote: This will be the last word I have on this topic. I have placed two files he www.k6mhe.com/n7ws/N7WS_Yagi_Resonant.EZ and he www.k6mhe.com/n7ws/N7WS_Yagi_Shortened.EZ The files are models of my 20-meter three-element Yagi that are as nearly representative of the physical antenna and its location as I can make them. The only difference between them is the half-length of the DE. The actual antenna uses the shortened version with a stub (Beta) matching/balun arrangement. Two photos of the details of this are he www.k6mhe.com/n7ws/YagiFeed-1a.jpg and he www.k6mhe.com/n7ws/YagiFeed-2a.jpg The photos were taken with the antenna mounted on the tower and the tower folded over in case you're wondering about the orientation. For the purposes of the discussion I have removed the stub matching system from the model. The following transformation and matching exercise can be performed using a Smith Chart, your favorite computer program or with pencil on the back of an envelope. I happen to prefer, and highly recommend, AC6LA's XLZIZL.xls Excel workbook for this stuff. First let's analyze the full-length, resonant DE version. After running the analysis we (should) have a feedpoint Z of 26.76 +j0 and a gain at the selected elevation of 12.91 dBi. The SWR is 1.87:1. Instead of the integral stub, which Yuri believes is part of the antenna that is "folded back" along the boom, I will move the matching system away from this location using an ideal ½ wavelength (34.7 foot) transmission line with an ideal current balun at the antenna end. I don't believe anyone would argue that the feedpoint impedance is not replicated exactly at the input end of this line. At the input end of the lossless line, the Z is of course, 26.76 +j0. Because, as will be shown, the stub matching system is nothing more than an L-network; I will use the same at the input of the half- wavelength line. I begin by inserting a series capacitor, C = 448 pF and Q = 1000. At the input side of this capacitor the Z is now: 26.785 -j25.062. If using XLZIZL, the loss in this capacitor is shown as 0.004 dB, because Q is not infinite. Continuing, I place a shunt inductor, L = 0.6, Q = 200 across the input of the series capacitor. The resulting input Z = 50.00 +j0.2. The total network loss is 0.02 dB. This is the baseline. Returning to the shortened driven element version, after analysis, we find that the input Z = 24.55 -j25.2 and the gain is unchanged at 12.91 dBi. At the input end of our magical ½ wavelength line, the Z remains 24.55 -j25.2. Once again using the L-network system, I find that the series capacitor is unnecessary and I can proceed by adding a shunt inductance. Rather than using Yuri's "preferred" discrete inductor, let's use a "lossy" stub. Instead of using the large diameter, parallel tube stub of the actual antenna, I'll use a standard transmission line for the stub. XLZIZL has a number if transmission lines and their parameters "built in," including the Wireman ladder lines. The parameters for these are those I derived in my ladder line paper. http://www.k6mhe.com/n7ws/Ladder_Line.pdf Selecting Wireman 553, shorting one end and placing the other in parallel with the input to the lossless line and doing a little manipulation and I find that a 14.85" length makes the Z = 50.12 +j0.18. The network loss remains 0.02 dB. So much for this less than ideal stub vs. Yuri's preferred discrete inductor. There you have it. The stub matching method is equal to a discrete L- network in efficiency, it does not detract from the antenna efficiency one bit, it can incorporate the balun function without additional components, it grounds the feedpoint, with a little sealant on the cable, it is weatherproof and unlike Gammas and Tee-matches, it will handle full power without being prone to capacitor breakdown. It is not part of the radiator; it is part of the matching network. Period. Hi Wes, A very interesting design and discussion. Thank you for posting it. I could be wrong but I think Yuri's main point was that if [fill in the blank] loading unit radiates at right angles to the beam pattern (or out of phase with it) it detracts from the gain of the antenna. I think that's probably a reasonable claim. 73, ac6xg |
Yagi antenna design question
"Wes" wrote in message
ups.com... This will be the last word I have on this topic. As: This is the last word from the higher authority, like, no more arguments, I am right, case closed? Just in case you might be wrong, here we go:-) I have placed two files he www.k6mhe.com/n7ws/N7WS_Yagi_Resonant.EZ and he www.k6mhe.com/n7ws/N7WS_Yagi_Shortened.EZ The files are models of my 20-meter three-element Yagi that are as nearly representative of the physical antenna and its location as I can make them. The only difference between them is the half-length of the DE. The actual antenna uses the shortened version with a stub (Beta) matching/balun arrangement. What you mean half length of DE? Resonant DE is 410.68" long Shortened DE is 399.64" long - that is 11.04" difference Resonant frequency on resonant model is 14.18 and shortened is 14.48 Instead of the integral stub, which Yuri believes is part of the antenna that is "folded back" along the boom, I will move the matching system away from this location using an ideal ½ wavelength (34.7 foot) transmission line with an ideal current balun at the antenna end. I don't believe anyone would argue that the feedpoint impedance is not replicated exactly at the input end of this line. Yuri believes? Is anyone there who does not believe that hairpin loading stub or beta match stub inserted in the middle of driven element is not the part of the element, aka, standing wave resonant circuit? Like there is no RF current flowing into the hairpin? Like element does not have to be shortened to compensate for the insertion of the stub? Doesn't Yagi antenna work with half wave (+-) resonant elements? If you loaded, inserted stubs in the parasitic elements, you would not have to shorten them? "Calculations" proving ??? snipped The network loss remains 0.02 dB. So much for this less than ideal stub vs. Yuri's preferred discrete inductor. There you have it. The stub matching method is equal to a discrete L- network in efficiency, it does not detract from the antenna efficiency one bit, it can incorporate the balun function without additional components, it grounds the feedpoint, with a little sealant on the cable, it is weatherproof and unlike Gammas and Tee-matches, it will handle full power without being prone to capacitor breakdown. It is not part of the radiator; it is part of the matching network. Period. Claiming that beta match or hairpin loading inductance is not the part of the radiator is news to me. Claiming that driven element was shortened to half, when in fact just by 11" and resonant frequency moved from abt 14.18 to 14.48 MHz, and modeling the antenna without the beta match hair pin, and then "calculating" 0.02 dB difference in gain, sure "proves" the point. Here I described the real life situation and modeling by using simple case of 40m dipole, resonant and resonant shortened with "beta match" hairpin. I maintain the resonant frequency and compensate for the effects of inserting the hairpin. The gain on the dipole drops by 0.15 dB when fed at the 75 ohm point and by 0.2 dB when fed close to 50 ohm point. You can read the rest at my web site: http://www.k3bu.us/beta_match.htm Again, it has ben proven by modeling and in practice that loading solenoid coils are better performers as loading element than hairpins, especially when better symetry along the element is important for bettern pattern and F/B. But I guess, that's another story to argue. Not the last word from me, if I am wrong and made error in modeling, I would like to be corrected. (I tried to post the EZNEC files, but having problem downloading them. Will try to rectify.) 73 Yuri, K3BU.us |
Yagi antenna design question
On Feb 10, 7:27 pm, "Yuri Blanarovich" wrote:
My previous ISP sold me off to a new one. SInce that time I've had no end of email problems and in addition the new guys don't provide newsgroups, so I've been reduced to using Google Groups. Yuch. I spent too much time composing a response to Yuri's last post and then did not see it appear after posting. I will not waste further time, but in a nutshell I offered another case using the self- reactance of the DE as part of the matching network. In this example, to avoid any "loss due to loading" resulting from shortening the DE, I *lengthen* the DE to obtain an inductive reactance for the series arm of an L-network and then use a shunt capacitor for the second matching element. The model is he http://www.k6mhe.com/n7ws/N7WS_Yagi_Lengthened.EZ Run the analysis, and add a shunt 195 pF and see what you get. Regards, Wes N7WS |
Yagi antenna design question
Looks like W8JI type of response: I am right, I will not respond to
questions and arguments and my is last word!" Fact 1. - When hairpin or beta match is inserted in the driven element or any resonant half wave dipole, it has current flowing through it. Fact 2. That element has to be shortened if resonance is to be maintained, which means that it is a center inductive loading element, hairpin, beta match is the part of the antenna standing wave circuit. Fact 3. There is current that would more, less belong to the antenna element flowing in the hairpin, folded on itself and on right angle to driven element, not contributing to overall current distribution. That can be seen in my EZNEC model in the article. That portion of the current is not in line with the rest of the element, it is missing from as to compared to full size element and therefore efficiency is slightly lower (middle part of the cosine wave is "missing" folded with hairpin). On typical 40m dipole, as I modeled, it accounts for about 0.2 dB loss. The original argument was is the beta match lossy or not. My modeling of the real situation is ignored, also findings and experimental verification of others who replaced hairpins with solenoid coils is ignored. What you are "arguing" is that if you place the matching network in the driven element (now you even lengthen it) that there is no loss. http://www.k3bu.us/beta_match.htm Is my modeling of 40m dipole wrong? Where? On dipole it shows about 0.2 dB loss, which gets bit more when used in multielement array. If you are denying that there is a RF antenna current flowing in the Beta match hairpin, then you are denying reality and I rest my case. No point of arguing or discussing when you do not show where I am wrong, but you offer "proof" by juggling matching components at the feedpoint. We are talking about hairpin that is part of the antenna element, has current flowing in the system and it has feedline attached at the feedpoint of element and hairpin. No tricks with coils or capacitors inserted half wave somewhere. 73 Yuri, K3BU.us We are not arguing loss due to loading, we are arguing - does hairpin beta match contribute to the loss in the system or not. I mentioned that there are better alternatives, if one choses to be less lossy. "Wes" wrote in message oups.com... On Feb 10, 7:27 pm, "Yuri Blanarovich" wrote: My previous ISP sold me off to a new one. SInce that time I've had no end of email problems and in addition the new guys don't provide newsgroups, so I've been reduced to using Google Groups. Yuch. I spent too much time composing a response to Yuri's last post and then did not see it appear after posting. I will not waste further time, but in a nutshell I offered another case using the self- reactance of the DE as part of the matching network. In this example, to avoid any "loss due to loading" resulting from shortening the DE, I *lengthen* the DE to obtain an inductive reactance for the series arm of an L-network and then use a shunt capacitor for the second matching element. The model is he http://www.k6mhe.com/n7ws/N7WS_Yagi_Lengthened.EZ Run the analysis, and add a shunt 195 pF and see what you get. Regards, Wes N7WS |
Yagi antenna design question
On Feb 12, 5:58 pm, "Yuri Blanarovich" wrote:
Looks like W8JI type of response: I am right, I will not respond to questions and arguments and my is last word!" Well: Point 1. What is wrong with a W8JI type of response? Point 2. I already violated my promise to remain silent on this thread, in the pointless belief that it might be possible to reason with you. How wrong I am. Fact 1. - When hairpin or beta match is inserted in the driven element or any resonant half wave dipole, it has current flowing through it. In my "lost" post, I addressed this. I said more-or-less, of course a stub, hairpin, beta, or whatever you would like to call it has current in it. If it didn't then it could be removed without effect. So what? Also if the stub is 1/4 lambda and shorted then the current is maximum at the short. Again, so what? Fact 2. That element has to be shortened if resonance is to be maintained, which means that it is a center inductive loading element, hairpin, beta match is the part of the antenna standing wave circuit. How about calling it a point rather than a fact? The real fact is that when shortened, the DE is no longer resonant. In an earlier post I said, and you apparently chose to ignore it or were too busy formulating a response to read: "Instead of the integral stub, which Yuri believes is part of the antenna that is "folded back" along the boom, I will move the matching system away from this location using an ideal ½ wavelength (34.7 foot) transmission line with an ideal current balun at the antenna end. I don't believe anyone would argue that the feedpoint impedance is not replicated exactly at the input end of this line. " Now when the hairpin, beta, or lumped inductor is 1/2 lambda away from the DE and it acts *exactly* the same, are you telling me that it is still part of the radiator and "loads" the DE? If you are saying yes, then this discussion really is over. If you will keep an open mind, let's say to keep the numbers easy, that the DE feedpoint when shortened appropriately is 25 -j25. At the input to an ideal 1/2 wavelength line, terminated with the DE, we will also see 25 -j25. The parallel equivalent of this (I should use admittences, but I'll leave it as impedance) is 50 || -j50. Shunting this with an inductive reactance +j 50 results in 50 +j0, or a perfect match. Now I suppose it can be argued that this is "resonating" the DE, although I would prefer to say the system is resonant. I don't see how you can argue that the added inductor is "radiating" or "subtracting" from the radiation of the DE, or whatever your point is. Nevertheless, you give it a try below. But I'm not sure Google is going to post this anyway, so I'm stopping here. I think the OP's original question has been answered: For all practical purposes, the radiation characteristics are unaffected by the matching scheme. Fact 3. There is current that would more, less belong to the antenna element flowing in the hairpin, folded on itself and on right angle to driven element, not contributing to overall current distribution. That can be seen in my EZNEC model in the article. That portion of the current is not in line with the rest of the element, it is missing from as to compared to full size element and therefore efficiency is slightly lower (middle part of the cosine wave is "missing" folded with hairpin). On typical 40m dipole, as I modeled, it accounts for about 0.2 dB loss. The original argument was is the beta match lossy or not. My modeling of the real situation is ignored, also findings and experimental verification of others who replaced hairpins with solenoid coils is ignored. What you are "arguing" is that if you place the matching network in the driven element (now you even lengthen it) that there is no loss.http://www.k3bu.us/beta_match.htm Is my modeling of 40m dipole wrong? Where? On dipole it shows about 0.2 dB loss, which gets bit more when used in multielement array. If you are denying that there is a RF antenna current flowing in the Beta match hairpin, then you are denying reality and I rest my case. No point of arguing or discussing when you do not show where I am wrong, but you offer "proof" by juggling matching components at the feedpoint. We are talking about hairpin that is part of the antenna element, has current flowing in the system and it has feedline attached at the feedpoint of element and hairpin. No tricks with coils or capacitors inserted half wave somewhere. 73 Yuri, K3BU.us We are not arguing loss due to loading, we are arguing - does hairpin beta match contribute to the loss in the system or not. I mentioned that there are better alternatives, if one choses to be less lossy. "Wes" wrote in message oups.com... On Feb 10, 7:27 pm, "Yuri Blanarovich" wrote: My previous ISP sold me off to a new one. SInce that time I've had no end of email problems and in addition the new guys don't provide newsgroups, so I've been reduced to using Google Groups. Yuch. I spent too much time composing a response to Yuri's last post and then did not see it appear after posting. I will not waste further time, but in a nutshell I offered another case using the self- reactance of the DE as part of the matching network. In this example, to avoid any "loss due to loading" resulting from shortening the DE, I *lengthen* the DE to obtain an inductive reactance for the series arm of an L-network and then use a shunt capacitor for the second matching element. The model is he http://www.k6mhe.com/n7ws/N7WS_Yagi_Lengthened.EZ Run the analysis, and add a shunt 195 pF and see what you get. Regards, Wes N7WS |
Yagi antenna design question
Wes,
you are ignoring my questions and modeled example showing the situation in question: resonant dipole loaded and with beta match vs. full size straight, reflecting the real life situation in question. You believe what you want. I have showed dipole element and EZNEC model of effect of beta match on performance of antenna: reduced gain, narrower bandwidth. It shows the current distribution along the element and the hairpin beta match. That current along the beta match is "taken out" of the element and causing reduction in gain and narrower bandwidth. Model shows that and measurements confirm that. This is just another application of the current along the antenna coil (loading element, hairpin, etc.), its effect on the current distribution along the radiator and corresponding efficiency. Believe it, or not! 73 Yuri, http://www.k3bu.us/beta_match.htm |
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