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Gamma-Match formulas--design?
Anyone work with the gamma-match to the point of becomming a guru?
I am looking for "Everything you wanted to know about a gamma-match--in a nutshell." In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? What conditions requiring a match is the gamma best suited for? What would need to be taken into consideration if one is using the match on a monopole? A dipole (T-match version)? A driven element in a yagi? A loop? Regards -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? |
John Smith wrote:
In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? EZNEC will give you ballpark answers that require some adjustments to length and capacitance. The free version of EZNEC is available at www.eznec.com. What conditions requiring a match is the gamma best suited for? When your electrical dipole is one piece of metal, i.e. a physical monopole. The center of 1/2WL of one piece of metal has the voltage equal to zero so you cannot feed it there but you can connect ground to there. Then feed it some distance away from center through a parallel element and a series capacitor. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
I am sorry, I abbreviate my questions and think everyone psychic and will
know what I am thinking, it is a fault of mine, many have pointed it out to me, I am working on correcting it (progress, as you can tell, has been slow)... let me attempt to correct my error. I am sure EZNEC is an excellent application. But with such applications, you spend your time learning the application, rather than the underlying principals; it requires you to structure yourself to fit the program. For my hobby efforts with antennas, I would rather just learn and possess the skills and do the calculations and design myself (I am rather eccentric this way.) Learning to rely on EZNEC I would just remain lazy and dependent on it and, un-knowledgeable to the math workings and methods underneath it. Since my son graduated college, I inherited his old "TI-83 Plus" programmable graphing calculator. I was looking more for the actual formulas and design methods to plug into the calculator--I would simply translate them to basic language (maybe later assembly, its' a Z80 processor.) The "Monopole" I had pictured in my mind was a 1/2 wave end-fed, but, I was not sure if the gamma would even be suitable for this use--and I attempted to leave my original question open-ended to catch this, if that was the case. I am glad you pointed out the center of a driven element, such as in a yagi, is "dead" and can be attached directly to ground. If a 1/2 end-fed monopole can be matched with gamma--would that still be the same case, only here the "end" could be attached to a grounded mast? Thank you for your reply, it is greatly appreciated. Warmest regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Cecil Moore" wrote in message ... John Smith wrote: In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? EZNEC will give you ballpark answers that require some adjustments to length and capacitance. The free version of EZNEC is available at www.eznec.com. What conditions requiring a match is the gamma best suited for? When your electrical dipole is one piece of metal, i.e. a physical monopole. The center of 1/2WL of one piece of metal has the voltage equal to zero so you cannot feed it there but you can connect ground to there. Then feed it some distance away from center through a parallel element and a series capacitor. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
John Smith wrote:
I am sure EZNEC is an excellent application. But with such applications, you spend your time learning the application, rather than the underlying principals; I have learned many, many principles from using EZNEC which is a really great learning tool. Look at it as reverse engineering. You wonder why EZNEC reports such results and then you go discover why. Modeling with ELNEC and EZNEC has taught me as much about antennas as any other single source including Dr. Balanis' graduate level college antenna course at ASU. One doesn't learn anything by avoiding learning EZNEC. Dr. Balanis was amazed that an Intel digital engineer already knew so much about antennas and I owe that, in large part, to ELNEC and EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Yes, I am quite sure you are correct.
And, perhaps no one knows, or no one does it the old fashioned way and has the formulas and steps at their disposal, I may have to seek other sources than here. However, I am a software engineer, once I understand the underlying math and methods I can write such an application myself. When the final drafts of these programs are released, antenna design, I am sure you will just draw your antenna on virtual graph paper with ruled lines, such as many of the draw programs have. And, be able to add any inductance or capacitance just by selecting the point with the mouse, and then entering values--the application will do everything else for you, including making suggestions for improvement, matching, special conditions, etc, etc--much like CAD (Computer Assisted Drafting) applications. However, whether I use software, or simply divide 468/Fmhz, I still get a half-wave. It is fine if one wants to rely on software--I make my living on those who do, I LOVE those people!--I just don't wish to invoke that method, later when my understanding is absolute (well, greater than it is now) I may, or write software specific to my needs... Warmest regards -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Cecil Moore" wrote in message ... John Smith wrote: I am sure EZNEC is an excellent application. But with such applications, you spend your time learning the application, rather than the underlying principals; I have learned many, many principles from using EZNEC which is a really great learning tool. Look at it as reverse engineering. You wonder why EZNEC reports such results and then you go discover why. Modeling with ELNEC and EZNEC has taught me as much about antennas as any other single source including Dr. Balanis' graduate level college antenna course at ASU. One doesn't learn anything by avoiding learning EZNEC. Dr. Balanis was amazed that an Intel digital engineer already knew so much about antennas and I owe that, in large part, to ELNEC and EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith"
wrote: I am looking for "Everything you wanted to know about a gamma-match--in a nutshell." In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? Hi Brett, That question rather goes beyond the nutshell lead-in. However, for the nutshell: 1/20th wave gamma rod; capacitance about 5 to 8pF/Meter-of-wavelength; gamma rod roughly half diameter as the radiator and spaced roughly 1/100th wavelength from it. With all the "roughlies" (a product of nutshell precision) it pays to make the capacitor a variable, or the gamma loop length variable. All such roughlies are also contingent upon the radiator's size WRT wavelength. To translate the capacitor characteristic: for 20M band it would be 100 to 160pF 73's Richard Clark, KB7QHC |
Richard:
Thank you Sir! This is information is exactly the type I was/am searching for. Warmest regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Richard Clark" wrote in message ... On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith" wrote: I am looking for "Everything you wanted to know about a gamma-match--in a nutshell." In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? Hi Brett, That question rather goes beyond the nutshell lead-in. However, for the nutshell: 1/20th wave gamma rod; capacitance about 5 to 8pF/Meter-of-wavelength; gamma rod roughly half diameter as the radiator and spaced roughly 1/100th wavelength from it. With all the "roughlies" (a product of nutshell precision) it pays to make the capacitor a variable, or the gamma loop length variable. All such roughlies are also contingent upon the radiator's size WRT wavelength. To translate the capacitor characteristic: for 20M band it would be 100 to 160pF 73's Richard Clark, KB7QHC |
John Smith wrote:
"In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value----?" It looks experimental to me. My ARRL Handbook says that the T match has an advantage in that a pair of transmission line attachment points equidistant from the center of a resonant wire has a resistance between them. Therefore it is possible to choose points which match the line Zo. Problem is the physical distance between the attachment points probably does not match the line spacing. The handbook suggests a T match made like a folded dipole with single-wire extensions at its ends. This looks as if it would require experimentation.. It seems suited for parallel-wire lines. The gamma match seems to be similar but an ubbalanced scheme where the grounded line conductor is attached to the center of the radiator and the ungrounded conductor is connected to the wire at a distance from the center of the radiator which results in a low SWR on the transmission line. A variation treats the gamma match as if it were a shunt tower feed arangement. The gamma match becomes a feed loop containing a ground path. The feed loop is sized to that required for a resistive component which matches the Zo of the transmission line. The loop inductively couples the antenna with the transmission line. The loop`s reactance is always inductive and can be tuned out with a series connected variable capacitor. It seems a good cut-and-try project to me. Maybe perfect for Art Unwin. Best regards, Richard Harrison, KB5WZI |
ok...
I cut a 1/2 wave monopole for 28.4Mhz and used the dimensions according to what you stated. The capacitor is homebrew from 3/16 acrylic sheet with aluminum plates, configured as a compression variable, true pf is unknown (with spacing and dielectric of acrylic and size of plates, should max at ~150 pf) --but plenty of adjustment, both sides of "null" on swr meter. However, the shorting bar on the gamma rod had to be raised to ~3 ft. (adjustment above or below this height only increases swr), here the swr is ~1.7:1. I cannot find a configuration on the gamma which brings the swr under that figure... lengthing/shorting monopole +2 to -2 inches has negligible effect and not for the better. Lenght of coax from rf source to ant seems critical, when coax is shortened or lengthened, gamma must be adjusted (but is always around 3 ft) The gamma rod length seems to be quite above what the figures you gave me would suggest (from what you suggested, 1/20 wave (~20 inches or do I have that correct?)--what am I too blind to see to see here, or what I am I ignorant of? Your continued help and advice would be most appreciated... Warmest regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Richard Clark" wrote in message ... On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith" wrote: I am looking for "Everything you wanted to know about a gamma-match--in a nutshell." In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? Hi Brett, That question rather goes beyond the nutshell lead-in. However, for the nutshell: 1/20th wave gamma rod; capacitance about 5 to 8pF/Meter-of-wavelength; gamma rod roughly half diameter as the radiator and spaced roughly 1/100th wavelength from it. With all the "roughlies" (a product of nutshell precision) it pays to make the capacitor a variable, or the gamma loop length variable. All such roughlies are also contingent upon the radiator's size WRT wavelength. To translate the capacitor characteristic: for 20M band it would be 100 to 160pF 73's Richard Clark, KB7QHC |
John Smith wrote:
I cannot find a configuration on the gamma which brings the swr under that figure... As Richard H. said, find the point where the feedpoint resistance is 50 + jXL ohms. That must occur somewhere. Then tune out the reactance with a series capacitor. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Sun, 3 Apr 2005 20:06:45 -0700, "John Smith"
wrote: Lenght of coax from rf source to ant seems critical, when coax is shortened or lengthened, gamma must be adjusted (but is always around 3 ft) Hi Brett, This is a classic symptom of feedline interaction with the feedpoint Impedance. Basically, the exterior of the cable is acting as an uncontrolled tuning element that is bridging your attempt to tune the antenna. To correct this one indication, you need to choke the feedline. This is accomplished by one of several methods. We frequently recommend what is called a "Current BalUn" which is a series of ferrite beads strung onto the coax near the feed point. Another method is to simply coil the coax with half a dozen turns of about 6 inches diameter. Either method will decouple the feedline from the feedpoint. There's more to be said, but that can be discussed at another time, or you can research that in the archives using the keywords in quotes above. This is successful with Low-Z loads because the choke is Hi-Z in comparison - your drive point choice presents a problem in that regard. That problem is that a halfwave is extremely sensitive to environment, especially in the face of unchoked lines. This is a fact of life in that for a Hi-Z load, nearly everything nearby looks like a short circuit unless you can hoist the antenna out of the way. The choking action will have to be extremely good to overcome this (or you will have to insure that the external coax length is also halfwave in length - this is one of those CB antenna/coax issues that rarely gets discussed and becomes lore instead of learning). Hi-Z loads are usually matched with Hi-Z circuits through voltage matching, the Gamma match is more a Low-Z device working as a current transformer. Its standard application, nearer the middle of the halfwave antenna, would be more suitable. To achieve this, isolate the bottom end of the halfwave (mount it on an insulator, the details which follow will be challenging). Make sure you can snake the coax up inside the antenna (this presumes it is tubular of sufficient diameter to pass cable up inside). Break out the cable halfway up (care must be given that this does not substantially weaken the whole of the antenna). Build the gamma match (external of course) here and drive it against the radiator body with one lead of the coax going to the gamma structure, the other side going to the break out hole. All in all, a SWR of 1.7 is not shabby for a first pass approximation for a physical solution. If you decide to stick with your current implementation, you might try making the gamma tube larger than the diameter of the radiator (capacitance stays the same). We are departing from the regime of nutshell math. By this (classical design), the work revealed in full sized, folded dipoles (and monopoles) teaches that the size ratio of the two elements (in this case approximated by the radiator and the gamma element), and their proximity, yield a step-up or step-down relationship in drive point Z (depending on which, larger or smaller, is being driven). This is like conventional transformer winding ratios, except in RF it is embodied in diameters and separation with complex results (not as simple as counting turns and being done with it). This is further complicated by the structure not being a classic folded design - I am merely extending the metaphor, returning this to nutshell theory. This means it is up to you to close the gap through experimentation, observation, and correlation. There may be a limit in what you can achieve, but you seem close enough to vary a few parameters to see if there is any progress. 73's Richard Clark, KB7QHC |
On Sun, 03 Apr 2005 21:47:02 -0700, Richard Clark
wrote: By this (classical design), the work revealed in full sized, folded dipoles (and monopoles) teaches that the size ratio of the two elements (in this case approximated by the radiator and the gamma element), and their proximity, yield a step-up or step-down relationship in drive point Z (depending on which, larger or smaller, is being driven). This is like conventional transformer winding ratios, except in RF it is embodied in diameters and separation with complex results (not as simple as counting turns and being done with it). This is further complicated by the structure not being a classic folded design - I am merely extending the metaphor, returning this to nutshell theory. Hi All, For others following my strained metaphors, consult Johnson and Jasik's "Antenna Engineering Handbook," "Impedance Transformation as a Function of the Ratio of Conductor Sizes" (pg. 4-17 of the second edition). This topic has always been confined to full sized folded quarterwave monopoles or halfwave dipoles and I have not observed any equal (that is, comprehensive) treatment given in terms of T or Gamma matches. Of course, there may be every reason why such has never been done. 73's Richard Clark, KB7QHC |
Yes, I understand about the transformer action of differing conductor sizes
at rf freqs. I interned for a tranformer manufacturer many moons ago. I will experment with differing diameters of the gamma rod. That is one new variable I can introduce.... Regards -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Richard Clark" wrote in message ... On Sun, 03 Apr 2005 21:47:02 -0700, Richard Clark wrote: By this (classical design), the work revealed in full sized, folded dipoles (and monopoles) teaches that the size ratio of the two elements (in this case approximated by the radiator and the gamma element), and their proximity, yield a step-up or step-down relationship in drive point Z (depending on which, larger or smaller, is being driven). This is like conventional transformer winding ratios, except in RF it is embodied in diameters and separation with complex results (not as simple as counting turns and being done with it). This is further complicated by the structure not being a classic folded design - I am merely extending the metaphor, returning this to nutshell theory. Hi All, For others following my strained metaphors, consult Johnson and Jasik's "Antenna Engineering Handbook," "Impedance Transformation as a Function of the Ratio of Conductor Sizes" (pg. 4-17 of the second edition). This topic has always been confined to full sized folded quarterwave monopoles or halfwave dipoles and I have not observed any equal (that is, comprehensive) treatment given in terms of T or Gamma matches. Of course, there may be every reason why such has never been done. 73's Richard Clark, KB7QHC |
Richard:
Thanks, I think you have at least one problem I created in check. I forgot to place ferrite beads over the coax, at the antenna, I guess I was thinking the gamma was some sort of increased isolation. It is now so apparent--now that you mentioned it... Regards -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Richard Clark" wrote in message ... On Sun, 3 Apr 2005 20:06:45 -0700, "John Smith" wrote: Lenght of coax from rf source to ant seems critical, when coax is shortened or lengthened, gamma must be adjusted (but is always around 3 ft) Hi Brett, This is a classic symptom of feedline interaction with the feedpoint Impedance. Basically, the exterior of the cable is acting as an uncontrolled tuning element that is bridging your attempt to tune the antenna. To correct this one indication, you need to choke the feedline. This is accomplished by one of several methods. We frequently recommend what is called a "Current BalUn" which is a series of ferrite beads strung onto the coax near the feed point. Another method is to simply coil the coax with half a dozen turns of about 6 inches diameter. Either method will decouple the feedline from the feedpoint. There's more to be said, but that can be discussed at another time, or you can research that in the archives using the keywords in quotes above. This is successful with Low-Z loads because the choke is Hi-Z in comparison - your drive point choice presents a problem in that regard. That problem is that a halfwave is extremely sensitive to environment, especially in the face of unchoked lines. This is a fact of life in that for a Hi-Z load, nearly everything nearby looks like a short circuit unless you can hoist the antenna out of the way. The choking action will have to be extremely good to overcome this (or you will have to insure that the external coax length is also halfwave in length - this is one of those CB antenna/coax issues that rarely gets discussed and becomes lore instead of learning). Hi-Z loads are usually matched with Hi-Z circuits through voltage matching, the Gamma match is more a Low-Z device working as a current transformer. Its standard application, nearer the middle of the halfwave antenna, would be more suitable. To achieve this, isolate the bottom end of the halfwave (mount it on an insulator, the details which follow will be challenging). Make sure you can snake the coax up inside the antenna (this presumes it is tubular of sufficient diameter to pass cable up inside). Break out the cable halfway up (care must be given that this does not substantially weaken the whole of the antenna). Build the gamma match (external of course) here and drive it against the radiator body with one lead of the coax going to the gamma structure, the other side going to the break out hole. All in all, a SWR of 1.7 is not shabby for a first pass approximation for a physical solution. If you decide to stick with your current implementation, you might try making the gamma tube larger than the diameter of the radiator (capacitance stays the same). We are departing from the regime of nutshell math. By this (classical design), the work revealed in full sized, folded dipoles (and monopoles) teaches that the size ratio of the two elements (in this case approximated by the radiator and the gamma element), and their proximity, yield a step-up or step-down relationship in drive point Z (depending on which, larger or smaller, is being driven). This is like conventional transformer winding ratios, except in RF it is embodied in diameters and separation with complex results (not as simple as counting turns and being done with it). This is further complicated by the structure not being a classic folded design - I am merely extending the metaphor, returning this to nutshell theory. This means it is up to you to close the gap through experimentation, observation, and correlation. There may be a limit in what you can achieve, but you seem close enough to vary a few parameters to see if there is any progress. 73's Richard Clark, KB7QHC |
J:
If the formulas, charts, etc. don't exist, then I am extremely lucky. Most of the time (OK! Maybe ALL the time) my efforts just end up duplicating what past expermenters have already done. I make notes as I go, if I don't find what I am doing in some other obscure work--or as knowledge another has, I will be tempted to place it in a form where others might use it. What I mean is, I will not be disappointed--and very happy if what you suspect is true. "Top Down" (hey, is that guy in a convertible?) is great, however, bottom up has its uses too... OOP(s) (a pun--Object Orientated Programing--for non-coders), I hope some of my old professors aren't around here! (Darn! that Richard, now he has me doing it) grin Regards -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "J. Mc Laughlin" wrote in message ... Dear John Smith (no call, no location) Your questions contain assumptions. You assume that formulas amiable of being programmed into a TI calculator exist for what it is you wish to do. I doubt that they exist. To borrow a term from your job, top-down is needed. Start with the ARRL's Antenna Book. When you have digested its teachings, read either Kraus' 3rd edition or Balanis' 2nd edition. Start at the beginning and follow the road. It will be an interesting journey. Regards, Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "John Smith" wrote in message ... Yes, I am quite sure you are correct. And, perhaps no one knows, or no one does it the old fashioned way and has the formulas and steps at their disposal, I may have to seek other sources than here. However, I am a software engineer, once I understand the underlying math and methods I can write such an application myself. When the final drafts of these programs are released, antenna design, I am sure you will just draw your antenna on virtual graph paper with ruled lines, such as many of the draw programs have. And, be able to add any inductance or capacitance just by selecting the point with the mouse, and then entering values--the application will do everything else for you, including making suggestions for improvement, matching, special conditions, etc, etc--much like CAD (Computer Assisted Drafting) applications. However, whether I use software, or simply divide 468/Fmhz, I still get a half-wave. It is fine if one wants to rely on software--I make my living on those who do, I LOVE those people!--I just don't wish to invoke that method, later when my understanding is absolute (well, greater than it is now) I may, or write software specific to my needs... Warmest regards "Cecil Moore" wrote in message ... John Smith wrote: I am sure EZNEC is an excellent application. But with such applications, you spend your time learning the application, rather than the underlying principals; I have learned many, many principles from using EZNEC which is a really great learning tool. Look at it as reverse engineering. You wonder why EZNEC reports such results and then you go discover why. Modeling with ELNEC and EZNEC has taught me as much about antennas as any other single source including Dr. Balanis' graduate level college antenna course at ASU. One doesn't learn anything by avoiding learning EZNEC. Dr. Balanis was amazed that an Intel digital engineer already knew so much about antennas and I owe that, in large part, to ELNEC and EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp |
Richard H.:
I had only used a "universal stub" and "L-Network" to match a 1/2 wave end fed before now. The gamma seems interesting. Just for my curriosity, I will do a full-wave with a T-Match in the next few days (seems a 1 wave vertical is best suited for high angle radiation pattern.) I will keep your analysis in mind, especially at that time--thanks! Regards -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Richard Harrison" wrote in message ... John Smith wrote: "In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value----?" It looks experimental to me. My ARRL Handbook says that the T match has an advantage in that a pair of transmission line attachment points equidistant from the center of a resonant wire has a resistance between them. Therefore it is possible to choose points which match the line Zo. Problem is the physical distance between the attachment points probably does not match the line spacing. The handbook suggests a T match made like a folded dipole with single-wire extensions at its ends. This looks as if it would require experimentation.. It seems suited for parallel-wire lines. The gamma match seems to be similar but an ubbalanced scheme where the grounded line conductor is attached to the center of the radiator and the ungrounded conductor is connected to the wire at a distance from the center of the radiator which results in a low SWR on the transmission line. A variation treats the gamma match as if it were a shunt tower feed arangement. The gamma match becomes a feed loop containing a ground path. The feed loop is sized to that required for a resistive component which matches the Zo of the transmission line. The loop inductively couples the antenna with the transmission line. The loop`s reactance is always inductive and can be tuned out with a series connected variable capacitor. It seems a good cut-and-try project to me. Maybe perfect for Art Unwin. Best regards, Richard Harrison, KB5WZI |
John Smith wrote:
Anyone work with the gamma-match to the point of becomming a guru? I am looking for "Everything you wanted to know about a gamma-match--in a nutshell." Start with the ARRL Antenna Book. My 19th Edition, (C) 2000, discusses gamma matches in chapter 26: Coupling the Line to the Antenna. In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? The best resource I've found for this is lecture notes by Dr. Thomas Montoya at: http://montoya.sdsmt.edu/ee492/fall2...2_fall2004.htm Glen, kc0iyt |
Well "John Smith," wherever and whoever you are, you are receiving valuable
advice from several quarters. Our students are required to use top-down programming in computer engineering and in computer science classes. If your professors did not convince you of its importance, far be it for me to try. Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: |
John Smith wrote:
Just for my curriosity, I will do a full-wave with a T-Match ... (seems a 1 wave vertical is best suited for high angle radiation pattern.) An *end-fed* one wavelength vertical fed against ground has a high angle radiation pattern, e.g. 36 deg TOA. A one wavelength vertical with a T-Match is a center-fed antenna. Such an antenna has a *low angle* radiation pattern, e.g. 11 deg TOA. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
John, do not allow yourself be led astray by the waffle on this
newsgroup of the importance of supposed antenna gains and the differences between one exaggerated radiation pattern and another. Real professsional radio engineers (who are extremely few and far between) who, to make an honest living, are obliged to work in the real world, and are accustomed to dealing with radio-path propagation uncertaintainties of plus or minus 10, 15 or even 20 dB. But perhaps you already find enough amusement with such silly back-to-front ratios as 50 dB and this little warning is unnecessary. I'm sure it is. ---- Reg. |
After so many waffling contributions to the newsgroup from you
'experts' - where is the Gamma-match design formula? There are only 2 or 3 dimensions involved. It should be simple and straightforward enough! Or is this newsgroup just a farce? ---- Reg. |
On Mon, 4 Apr 2005 15:56:39 +0000 (UTC), "Reg Edwards"
wrote: Or is this newsgroup just a farce? Hi Reggie, Surely at your age, and experience writing here, you MUST know the answer to that by now. 73's Richard Clark, KB7QHC |
Reg:
Your point is well taken here. I was wondering if it was just me and, I ended up throwing away valuable posts because I was unable to recognize pertinent posts; some posts do leave me asking a question, "Why would some authors even post replies which contain no useable facts, data, and comments--what is their intent?" In the end, I chalked it up to, perhaps, younger people entering the arena of discussion in "the real world" and, perhaps it would take them a bit of time to experience what works and what does not. Whatever this phenomenon is, your comments have been reassuring to my not being alone in observing this behavior, THANKS! Warmest regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Reg Edwards" wrote in message ... After so many waffling contributions to the newsgroup from you 'experts' - where is the Gamma-match design formula? There are only 2 or 3 dimensions involved. It should be simple and straightforward enough! Or is this newsgroup just a farce? ---- Reg. |
On Sun, 3 Apr 2005 13:24:27 -0700, "John Smith"
wrote: [snip] The "Monopole" I had pictured in my mind was a 1/2 wave end-fed, but, I was not sure if the gamma would even be suitable for this use--and I attempted to leave my original question open-ended to catch this, if that was the case. I am glad you pointed out the center of a driven element, such as in a yagi, is "dead" and can be attached directly to ground. If a 1/2 end-fed monopole can be matched with gamma--would that still be the same case, only here the "end" could be attached to a grounded mast? The gamma is normally used to feed the center of the driven element of a Yagi where the feedpoint impedance is lower than that of the transmission line and it is desired to have an unbroken element. Another application is to shunt feed a grounded monopole, such as when a grounded tower is used as a radiator. In this case too, the base impedance is lower than the transmission line Z. Both cases use the gamma as an impedance "step-up" transformer. Because you suggest an end-fed half-wave, where the impedance is much greater than 50-70 Ohm, I see no compelling reason to opt for a gamma feed, other than the case when you want to ground the end of the radiator (which may be what you have in mind). While it is convenient to think of the gamma as a system where a "50 Ohm point" is located on the radiator and a tap made to it, the reality is that the system is *much* more complicated and involves mutual coupling, transmission line effects, etc, between the gamma rod and the radiator. A moments reflection (no pun intended) will make this obvious. If a "50 Ohm point" is the only goal then the gamma rod diameter and spacing would not be factors. Additionally, there is a multiplicity of combinations that will present a match, at one frequency. Each will have a different effective bandwidth, however. Suggested reading: "A New Look at the Gamma Match", QEX, May/June 1999, pp 23-31 |
On Mon, 04 Apr 2005 10:10:44 -0700, Wes Stewart
wrote: [snip] Another application is to shunt feed a grounded monopole, such as when a grounded tower is used as a radiator. In this case too, the base impedance is lower than the transmission line Z. Before I'm taken to task, let me add, "is usually lower" than the transmission line Z.\ Shunt feeding can be/is done on towers longer than 1/4 wavelength where the Z at the bottom of the tower is higher than Zo. |
J:
College was and is a great institution. However, the most valuable professors/instructors I ever had the pleasure to study under seemed to share one common element--they had all first worked in private enterprise before entering the academic professions (scouting rounds a guy out!) My first degree was in electronic engineering. When the focus of this seemed to move off shore and other employment opportunities became available (and the Apple, then the IBM PC, came to be), I returned to college and focused my attention in the field of computer science. Being an older student at that time and possessing a bit of "street-smarts", I was able to side step issues which I had found NOT be in "vogue" of my instructors beliefs. Although these institutions are a great forum for debate and argument--I was able to see little value in endangering my grades with such which would be contrary to my instructors favorite pet ideas (indeed, while in their classrooms, they all thought--I thought, they were the most handsome (or beautiful--if female) and gifted instructor(s) I ever had the pleasure to study under grin.) Some instructors are quick to point out, "There are NO dumb questions, just dumb people who don't ask questions." However, although they may state the above--following their own advice seemed to be a bit more of a challenge to many of them and, some were better in the implementation of that ideal than others; somehow, it left me with the opinion that a more accurate translation to this advice would have been, "If you don't agree with me and the course material I have chosen for this course--YOU WILL PAY!" But, I make no mistake--I am humbly indebted to ALL instructors for their time and efforts--I value all who lives I touched in those hallowed halls. To this day, I do work with encryption/decryption methods and protocols. Frequently I employ another questionable practice--security through obscurity; this fills my dreams with seemingly psychic visions of past instructors cringing in dark corners in loathing contempt and fear of such arcane and cheap methods... Rather frequently I utter (under my breath), "Whatever works!" guilty smile Warmest regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "J. Mc Laughlin" wrote in message ... Well "John Smith," wherever and whoever you are, you are receiving valuable advice from several quarters. Our students are required to use top-down programming in computer engineering and in computer science classes. If your professors did not convince you of its importance, far be it for me to try. Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: |
Cecil:
I stand corrected... Warm regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Cecil Moore" wrote in message ... John Smith wrote: Just for my curriosity, I will do a full-wave with a T-Match ... (seems a 1 wave vertical is best suited for high angle radiation pattern.) An *end-fed* one wavelength vertical fed against ground has a high angle radiation pattern, e.g. 36 deg TOA. A one wavelength vertical with a T-Match is a center-fed antenna. Such an antenna has a *low angle* radiation pattern, e.g. 11 deg TOA. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Wes:
I believe you are correct--my use of the gamma is rather unconventional here (how would one describe this antenna, "A J-Pole without 1/4 wave matching section?", having been replaced with the gamma.) However, my first impressions from my limitied observations is that there IS an increase in received signal strength from the most distant stations, and appearing as 1-2 S-units with the use of a gamma match (ok, maybe something else is responsible--but I can't see it.) The gamma I am using is constructed of all copper (3/8 tubing at the moment) with soldered connections, other than the sliding clamp attaching it to the end fed monopole (copper clamp to the copper element of the monopole)--it replaces an L-Network of #8 copper wire using a capacitor of copper plates and telflon dielectric material. Unless there is another varible at work--the gamma side of the monopole seems to have a bit more of the patterns favor--but barely noticeable (spacing of the gamma rod from monopole is ~4 inches.) Regards, John -- Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw aboot speel-checkin it fer me? "Wes Stewart" wrote in message ... On Sun, 3 Apr 2005 13:24:27 -0700, "John Smith" wrote: [snip] The "Monopole" I had pictured in my mind was a 1/2 wave end-fed, but, I was not sure if the gamma would even be suitable for this use--and I attempted to leave my original question open-ended to catch this, if that was the case. I am glad you pointed out the center of a driven element, such as in a yagi, is "dead" and can be attached directly to ground. If a 1/2 end-fed monopole can be matched with gamma--would that still be the same case, only here the "end" could be attached to a grounded mast? The gamma is normally used to feed the center of the driven element of a Yagi where the feedpoint impedance is lower than that of the transmission line and it is desired to have an unbroken element. Another application is to shunt feed a grounded monopole, such as when a grounded tower is used as a radiator. In this case too, the base impedance is lower than the transmission line Z. Both cases use the gamma as an impedance "step-up" transformer. Because you suggest an end-fed half-wave, where the impedance is much greater than 50-70 Ohm, I see no compelling reason to opt for a gamma feed, other than the case when you want to ground the end of the radiator (which may be what you have in mind). While it is convenient to think of the gamma as a system where a "50 Ohm point" is located on the radiator and a tap made to it, the reality is that the system is *much* more complicated and involves mutual coupling, transmission line effects, etc, between the gamma rod and the radiator. A moments reflection (no pun intended) will make this obvious. If a "50 Ohm point" is the only goal then the gamma rod diameter and spacing would not be factors. Additionally, there is a multiplicity of combinations that will present a match, at one frequency. Each will have a different effective bandwidth, however. Suggested reading: "A New Look at the Gamma Match", QEX, May/June 1999, pp 23-31 |
John Smith wrote:
Reg: Your point is well taken here. I was wondering if it was just me and, I ended up throwing away valuable posts because I was unable to recognize pertinent posts; some posts do leave me asking a question, "Why would some authors even post replies which contain no useable facts, data, and comments--what is their intent?" In the end, I chalked it up to, perhaps, younger people entering the arena of discussion in "the real world" and, perhaps it would take them a bit of time to experience what works and what does not. Whatever this phenomenon is, your comments have been reassuring to my not being alone in observing this behavior, THANKS! Warmest regards, John (Sigh!) I put all the gamma match info I have on a.b.s.e (I think; it hasn't appeared there yet)under subject "Gamma match article and executable." One is an article in PDF format and the other is a DOS executable for designing. Use whichever one floats your boat. John - KD5YI |
Reg Edwards wrote:
After so many waffling contributions to the newsgroup from you 'experts' - where is the Gamma-match design formula? There are only 2 or 3 dimensions involved. It should be simple and straightforward enough! Reg, is this the question? Where is the ratio of the real part of the net voltage to the real part of the net current equal to 50 ohms? Or is it more complicated than that? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
John Smith wrote:
"Why would some authors even post replies which contain no useable facts, data, and comments--what is their intent?" My Mother had a take on such folk: They're just talking to hear their heads rattle. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
John Smith wrote:
Cecil: I stand corrected... John, more like "I stand expanded." I wasn't correcting you. I was just expanding upon your statement. You were entirely correct about a one wavelength vertical end-fed against ground. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Just to take a side avenue to this all, I dropped down another 1/2 wave
element adjacent to 1/2 monopole under discussion, with a shorting strap the top of the elements (converting the 1/2 monopole into an upside down "U"--or, resembling a slim-jim with 1/4 wave match replaced by the gamma), guess what? Yes, a noticible improvement.... Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Reg Edwards" wrote in message ... After so many waffling contributions to the newsgroup from you 'experts' - where is the Gamma-match design formula? There are only 2 or 3 dimensions involved. It should be simple and straightforward enough! Or is this newsgroup just a farce? ---- Reg. |
Glen:
THAT is a very interesting URL, thank you for the time in bringing it to my attention; it is apparent that my internet searchs are missing important documents! Dr. Montoya is "my kinda guy." Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Glen Overby" wrote in message ... John Smith wrote: Anyone work with the gamma-match to the point of becomming a guru? I am looking for "Everything you wanted to know about a gamma-match--in a nutshell." Start with the ARRL Antenna Book. My 19th Edition, (C) 2000, discusses gamma matches in chapter 26: Coupling the Line to the Antenna. In other words, what set of formulas would give you length, conductor spacing, gamma capacitor value, ratio of gamma rod to driven element diameter, and a starting measurement for the shorting bar between conductors-- for a given frequency? The best resource I've found for this is lecture notes by Dr. Thomas Montoya at: http://montoya.sdsmt.edu/ee492/fall2...2_fall2004.htm Glen, kc0iyt |
John Smith wrote:
"In other words, what set of formulas would give you length, conductor spacing, hgamma capacitor value---?" Arnold W.P. King was author of the Antennas section of "Transmission Lines, Antennas, and Wave Guides", McGraw-Hill, 1945. Wing wrote "Transmission Lines". Mimno wrote "Wave Guides". On page 158, King wrote: "---it is possible to modify the antenna itself in such a way that the input impedance at its terminals is equal to the characteristic impedance of the line. The usual arrangement, Hig. 28.3, is to attach conductors at points CD along the antenna (which are not sufficiently close to the near zone) and join these to the input terminals at AB. The accurate calculation of the input impedance at AB of the modified antenna as a function of the resistance CD and the lengths AC and BD has not been accomplished." I wouldn`t hold my breath waiting for accurate formulas, but you are free to try it yourself. The gamma match is similar to the delta match and must cope with some of the same problems. This may be a case for experimentation. Best regards, Richard Harrison, KB5WZI |
O.K. Reg
I'll take you up on the 50 db F/B. There are old wives tales and then there are old wives who just tell tales about other old wives.Which is it? I have never read anything definitive about max F/B figures attainable. I have heard unsubstantiated stories about narrow voids filling up between lobes but no data to back it up so I would call that an old wives tale. There are computor programs that show large F/B figures, shall we throw those away together with your programs as computor programs are all suspect? Actually I have not seen any measured data regarding F/B radiation with respect to lobe angles possibly because of difficulties with respect to measuring And also what height the antenna must be before lobe shapes stablises.? Now you have come forward and stated, presumably by experience, mathematics or what ever, that 50 db F/B is silly. Why so? What F/B figure is not silly and why, plus what are the parameters involved that make this F/B not silly? Does this F/B relate to all antennas, yagi's, dish forms, verticals, wire arrangements or what? I am so pleased somebody has all this data so as to really substantiate, without doubt, that it really IS an old wives tale ,or is it somebody just exercising their right to free speech regardless of content. I await your reply with interest, and ofcourse, the scientific data that substantiate what IS an old wives tale and what IS not, and........ without "waffle" Regards Art Unwin...KB9MZ....XG "Reg Edwards" wrote in message ... John, do not allow yourself be led astray by the waffle on this newsgroup of the importance of supposed antenna gains and the differences between one exaggerated radiation pattern and another. snip But perhaps you already find enough amusement with such silly back-to-front ratios as 50 dB and this little warning is unnecessary. I'm sure it is. ---- Reg. |
To all:
Well, conductor diameter is not very critical in this configuration (or, at least that appears true to me--strange as that is to swallow.) However, the gamma rod I now have is #8 copper wire. And, that works out well, although it needs a couple of extra insulating spacers to stabilize it to the monopole, it is easy to work with and one only needs to solder it to the copper monopole, it can be bent and straightened at will to adjust spacings-shortened and lengthened by soldering on a bit. Richard reminding me of the necessity of ferrite beads has made the tuning of gamma much smoother, and an swr of 1.4:1 is now had--coax length changes are MUCH less noticeable--bordering on trivial. As it stands now, it is 32 ft. to the bottom of the monopole. The very bottom of the monopole is connected to the aluminum mast, the mast is well grounded (static and lighting protection are a given.) The monopole is now in the configuration of a 1 wave folded monopole (end fed through a gamma.) Placing the gamma in the middle of the two vertical lengths of the monopole (at the bottom end of the open "U") seems to give a complete 360 degree EVEN pattern, no noticeable bumps (perhaps a very slight elongation of the lobes in the same plane as the two ends of the folded monopole.) From my simple observations, I put the most weight in s-unit readings of known signals I RECEIVE with a known transceiver and coax (this I consider to be the most "real world" test I can devise.) This configuration is, by far, the best I have had sitting on that mast. It blows away the 1/4 wave I constructed (I am too worn out to put back the 1/4 and note the exact differences, but a safe estimate is 4+ s-units on all known received signals here on the valley floor. This has to be a low pattern, but critique and comments are welcomed to contest this.) It might be my imagination, but there seems a very "solid" sound and feel to signals (this is impossible to measure and will make many--if not all--doubt my sanity!) As some have noted, the humble s-unit will vary widely on transceivers, and is fallible... However, now I have an antenna of a, somewhat, seemingly unique configuration which will give me a good conversation piece to chew over with friends.... I am pressing this antenna into everyday use while I throw another together to toy with the gamma on. One more thing. I have found a beacon on 27.125 (Chicken Band Channel 14.) It is on the air 24/7. It is a 20 MW child's walkie-talkie with a 9 ft. antenna. It repeats the letters (call) "AOH" repeatedly at 7 wpm. I have had email correspondence with the operator ", the above details gleaned through such. He/she claims it has been heard throughout northern and central California, and that it is located high atop Mt. Diablo here in California. It has been an asset in testing the antenna(s) in receive conditions, under varying conditions, in "the real world." Summary and conclusions: -The gamma can be used to match a 1/2 wave end fed monopole with acceptable results. -The gamma can be used to match a 1 wave end fed folded monopole with acceptable results. -The 1 wave folded monopole seems a superior element to use in this design. -Although only suspicion at this point, I suspect the gamma to be of slightly less "lossy" performance than the L-Match previously used and/or provides a more favorable "launch" to the radiation pattern desired--more attention needs to be given this in future experiments. The experiments continue. Thanks all for your past and continuing assistance and council... Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "John Smith" wrote in message ... Just to take a side avenue to this all, I dropped down another 1/2 wave element adjacent to 1/2 monopole under discussion, with a shorting strap the top of the elements (converting the 1/2 monopole into an upside down "U"--or, resembling a slim-jim with 1/4 wave match replaced by the gamma), guess what? Yes, a noticible improvement.... Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Reg Edwards" wrote in message ... After so many waffling contributions to the newsgroup from you 'experts' - where is the Gamma-match design formula? There are only 2 or 3 dimensions involved. It should be simple and straightforward enough! Or is this newsgroup just a farce? ---- Reg. |
Art, KB9MZ wrote:
"O.K. Reg, I`ll take you up on the 50 dB F/B." It requires good balance for such cancellation. Kraus gives the gain for a 100-meter dish near Bonn, Germany on page 676 of the 3rd edition of "Antennas". Gain is a function of frequency and varies from about 48 dB at 300 MHz to about 98 dB at 150 GHz. I don`t know if shielding has been added to make this a "high-performance" dish but I would wager that this enormous radio ear and mouth has an excellent front-to-back ratio. Probably exceeds forward gain at some azimuths and elevation angles. Arnold B. Bailey has a lot to say anout a "connected" (driven) element and a parasitic reflector, starting about on 447 of "TV and Other Receiving Antennas", Bailey says: "The optimum spacing for highest gain of a parasitic reflector is S=0.15 wavelength plus or minus 0.025. Here the relleector is operated at Q=+1 (longer than resonant) and the gain in direction 1 is approximately 5.5 dB. Reasonable compromise for a less critical system is to use a spacing of 0.2 wavelength and a parasitic element longer than resonant (at Q=+1). This case gives a gain in direction 1 of 5 dB." On page 440 Bailey says: The front-to-back ratio ---is 17.5 dB in this case, and the Y/X ratio only about 9 dB, where +X represents the optimum direction.---" A picture is worth 1000 words. Best regards, Richard Harrison, KB5WZI |
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