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Linear decoupling traps
I am planning a two band antenna for 30 and 80m using linear traps.
The idea is to build the antenna of zip-cord type line 140ohm vf 0.73. Trap is made using 1/4 wave shorted stub, decoupling occurs at the open end. My question: Is there any difference if the shorted end is pointing to the center or to the tip of dipole. Only the stub portion has two wires in parallell, the rest is only one wire. ----------------------------------------xxcenterxxx---- I_________ OR ----------------------------------------xxxxcenterxxx------ ________I 73 Jouko OH5RM |
Linear decoupling traps
On Apr 12, 11:54*am, "JN" wrote:
I am planning a two band antenna for 30 and 80m using linear traps. 73 Jouko OH5RM Jouko.......you might try to GOOGLE: "lattin antenna" That may lead you to useful information. Lee KA0FPJ |
Linear decoupling traps
Jouko.......you might try to GOOGLE: "lattin antenna" That may lead you to useful information. Lee KA0FPJ Yes Lee, Google found quite a lot of hits, but they all refer to one 5band antenna design with no much real information. So my question still remains open. Could some modelling program give the answer? I think those two alternatives differ at least in how much inductive loadind they are causing to the lower frequency and so shortening the total length of antenna. Jouko OH5RM |
Linear decoupling traps
On Tue, 15 Apr 2008 11:39:04 +0300, "JN" wrote:
Jouko.......you might try to GOOGLE: "lattin antenna" That may lead you to useful information. Yes Lee, Google found quite a lot of hits, but they all refer to one 5band antenna design with no much real information. So my question still remains open. Could some modelling program give the answer? I think those two alternatives differ at least in how much inductive loadind they are causing to the lower frequency and so shortening the total length of antenna. Hi Jouko OH5RM Yes modeling can give an answer: NO It does not work. 73's Richard Clark, KB7QHC |
Linear decoupling traps
Hi Jouko OH5RM
Yes modeling can give an answer: NO It does not work. 73's Richard Clark, KB7QHC Hi Richard, Sorry I didnt quite understand your short answer. What does not work? The whole principe of decoupling stubs? Unfortenately I myself have no modelling program. 73 Jouko OH5RM |
Linear decoupling traps
On Tue, 15 Apr 2008 19:48:53 +0300, "JN" wrote:
Hi Jouko OH5RM Yes modeling can give an answer: NO It does not work. 73's Richard Clark, KB7QHC Hi Richard, Sorry I didnt quite understand your short answer. What does not work? The whole principe of decoupling stubs? Unfortenately I myself have no modelling program. Hi Jouko, Basically, what you describe was discussed here last week as the W9INN dipole, and recently as the Lattin dipole. Being the same thing as your twin line (parallel line, or folded stub, or whatever); the premise is these elements resonate and thus trap an antenna for multiband operation. Those stubs are not oriented correctly. Let's take this by degrees. Any dipole is a multiband antenna. Those bands might be useful, and they might not. The point is that being multiband is nothing remarkable in itself. What is remarkable is if that antenna is useful in every band you want to use it in. This is the "Holy Grail." Nearly 60 years ago, a Ham invented the Lattin antenna. We cannot say it was designed because it never performed according to claims (and I do mean NEVER). It was even patented. Designs do work, inventions rarely do. We get inventors here every week, some hang around for years. The bottom line is that if these inventions worked, we would be using them (and that is 2% of the goal of these inventors, the other 98% is seeking validation as being eminent thinkers). The Lattin antenna's balance sheet shows 1PPM usage, and no pursuit of validation (the inventor is dead, but some still keep the vigil and change the flowers at Internet memorial sites). You can try your hand at modeling by visiting: http://www.eznec.com/ The Lattin design is easily constructed by a model, I've done several dozen variations. You can also model stubs that are oriented correctly and that will work. 73's Richard Clark, KB7QHC |
Linear decoupling traps
Richard thanks for your answer and opinions.
I am not talking abt Lattin or W9INN. These are things I hear in this thread for the first time. I am talking abt using 1/4 wave stub as decoupling element to make a (reduced size?) two band antenna. This principle is used in commercial antennas like HY-GAIN AT-18 tower vertical and many others, stubs in line with element. Orr in his antenna book is using orientation, open to center.but in line with the element So I am sure the principle works ok, and I was asking abt the different orientation alternatives. I understand that you would suggest 90 degree? But does it really matter? Designs do work, inventions rarely do. Yes I agree. Therefore I am not going to build any complex mess where everything is hanging of everything, just simple one time decoupling the element for higher fequency. 73 Jouko OH5RM |
Linear decoupling traps
Richard Clark wrote:
The Lattin design is easily constructed by a model, I've done several dozen variations. You can also model stubs that are oriented correctly and that will work. Modeling real-world lossy stubs seems to violate EZNEC's guidelines. How does one do it? -- 73, Cecil http://www.w5dxp.com |
Linear decoupling traps
JN wrote:
So I am sure the principle works ok, and I was asking abt the different orientation alternatives. I understand that you would suggest 90 degree? But does it really matter? The series stub can be coiled in a circle as a lot of commercial antennas do. -- 73, Cecil http://www.w5dxp.com |
Linear decoupling traps
On Tue, 15 Apr 2008 21:44:02 +0300, "JN" wrote:
I understand that you would suggest 90 degree? But does it really matter? Hi Jouko, At right angles, yes. Does it matter? That depends on proximity to other conductors, including itself if you "coil" it around the radiator, or along the radiator. When I looked at your first posting, I was confused by the single wire, and the text graphics should have been done in fixed font. Keep the line conductors at least 3, preferably more, wire diameters from the radiator or themselves. Use the largest diameter for the multiplier of 3 (or more). 73's Richard Clark, KB7QHC |
Linear decoupling traps
On Tue, 15 Apr 2008 13:46:08 -0500, Cecil Moore
wrote: Modeling real-world lossy stubs seems to violate EZNEC's guidelines. How does one do it? One does not get hyperbolic about trivialities. |
Linear decoupling traps
..
----------------------------------------xxcenterxxx---- I_________ OR ----------------------------------------xxxxcenterxxx------ ________I 73 Jouko OH5RM Different text sizes seem to destroy the graphics, I used the medium size in Outlook express. Anyway the upper is OK , the lower should look like this ______________________________________/center/_____ ___________I OH5RM |
Linear decoupling traps
On Wed, 16 Apr 2008 09:21:13 +0300, "JN" wrote:
. ----------------------------------------xxcenterxxx---- I_________ OR ----------------------------------------xxxxcenterxxx------ ________I 73 Jouko OH5RM Different text sizes seem to destroy the graphics, I used the medium size in Outlook express. Anyway the upper is OK , the lower should look like this ______________________________________/center/_____ ___________I OH5RM from OP My question: Is there any difference if the shorted end is pointing to the center or to the tip of dipole. Only the stub portion has two wires in parallell, the rest is only one wire. Jouko, I noticed this thread took a detour, but I never saw anyone actually try to answer your question. I too, am looking to see the answer on this. It is amazing, all this talk about a Lattin antenna, that appears to have lots of sites talking about how it works, but no one actually having built one or used one, and a simple "yes" or "no" would answer your question. I don't have the answers or the means of testing one at this time. If you get the answer direct, please post it here. Thanks Buck N4PGW -- 73 for now Buck, N4PGW www.lumpuckeroo.com "Small - broadband - efficient: pick any two." |
Linear decoupling traps
Jouko, I noticed this thread took a detour, but I never saw anyone
actually try to answer your question. I too, am looking to see the answer on this. 73 for now Buck, N4PGW www.lumpuckeroo.com Yes Buck it is often difficult to get an answer just to the question you are asking. Anyway very soon all snow has melted away here and then its possible to testbuild it. 73 Jouko OH5RM |
Linear decoupling traps
"JN" wrote in message ... Jouko, I noticed this thread took a detour, but I never saw anyone actually try to answer your question. I too, am looking to see the answer on this. 73 for now Buck, N4PGW www.lumpuckeroo.com Yes Buck it is often difficult to get an answer just to the question you are asking. Anyway very soon all snow has melted away here and then its possible to testbuild it. 73 Jouko OH5RM Hi Jouko I thought Richard's statement that modeling would tell you about how the design might perform, was good advice. If you use EZNEC, I'd be willing to help you if you dont already know how to use it to model your antenna. Jerry KD6JDJ |
Linear decoupling traps
On Wed, 16 Apr 2008 17:01:24 +0300, "JN" wrote:
Jouko, I noticed this thread took a detour, but I never saw anyone actually try to answer your question. I too, am looking to see the answer on this. 73 for now Buck, N4PGW www.lumpuckeroo.com Yes Buck it is often difficult to get an answer just to the question you are asking. Anyway very soon all snow has melted away here and then its possible to testbuild it. 73 Jouko OH5RM Repeated message seeing that you both missed it: On Tue, 15 Apr 2008 21:44:02 +0300, "JN" wrote: I understand that you would suggest 90 degree? But does it really matter? Hi Jouko, At right angles, yes. Does it matter? That depends on proximity to other conductors, including itself if you "coil" it around the radiator, or along the radiator. When I looked at your first posting, I was confused by the single wire, and the text graphics should have been done in fixed font. Keep the line conductors at least 3, preferably more, wire diameters from the radiator or themselves. Use the largest diameter for the multiplier of 3 (or more). 73's Richard Clark, KB7QHC 73's Richard Clark, KB7QHC |
Linear decoupling traps
Richard Clark wrote:
Cecil Moore wrote: Modeling real-world lossy stubs seems to violate EZNEC's guidelines. How does one do it? One does not get hyperbolic about trivialities. Is 24 dBi omnidirectional gain from a vertical antenna enough to "get hyperbolic about trivialities"? http://www.w5dxp.com/SUPRGAIN.EZ -- 73, Cecil http://www.w5dxp.com |
Linear decoupling traps
HI
Theory says that whatever condition exists at far end of 1/4 wave stub will appear at fed end. ie. if far end is left open a high impedance will appear at fed end, at resonant freq. So it would appear that the shorted end should be nearest to feed point of antenna. The centre of dipole or bottom of a vertical. Hope that makes sense!................................Rod EI3CZ |
Linear decoupling traps
I thought Richard's statement that modeling would tell you about how the
design might perform, was good advice. If you use EZNEC, I'd be willing to help you if you dont already know how to use it to model your antenna. Jerry KD6JDJ Jerry, thanks for the offert. I dont know how good these modelling programs are in this situation. But if it is easy, so could somebody do the following: Take 20m of wire, that is half of a dipole. Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end is 7,25m from center and the shorted end pointing to the tip of antenna. One side of stub is the 20m wire itself, like in the upper picture. Ignore all velocity factors to make it sinple. Now tell me what are the resonance frequencies of that kind of element and if possible feed point impedande (80m and 30m) I know I could do it myself but as you know learning to use a new program reliably takes lot of time. 73 Jouko OH5RM |
Linear decoupling traps
"JN" wrote in message ... I thought Richard's statement that modeling would tell you about how the design might perform, was good advice. If you use EZNEC, I'd be willing to help you if you dont already know how to use it to model your antenna. Jerry KD6JDJ Jerry, thanks for the offert. I dont know how good these modelling programs are in this situation. But if it is easy, so could somebody do the following: Take 20m of wire, that is half of a dipole. Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end is 7,25m from center and the shorted end pointing to the tip of antenna. One side of stub is the 20m wire itself, like in the upper picture. Ignore all velocity factors to make it sinple. Now tell me what are the resonance frequencies of that kind of element and if possible feed point impedande (80m and 30m) I know I could do it myself but as you know learning to use a new program reliably takes lot of time. 73 Jouko OH5RM Hi Jouko I am not sure I am reading your text properly. But, I did model a 40 meter wire with a trap on each side. You are welcome to E-mail me if you want to see what EZNEC says about *my* model. Maybe you can help me model your concept. I have a friend in vasa Finland who can get you any information about contacting me. Google Patrik Tast. Jerry KD6JDJ |
Linear decoupling traps
Jouko, OH5RM wrote:
Take 20m of wire, that is half of a dipole. Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end is 7,25m from center and the shorted end pointing to the tip of antenna. One side of stub is the 20m wire itself, like in the upper picture. I did just that with EZNEC, but with a free-space dipole. Without the stubs, the antenna resonated at 3.6 MHz. With the stubs, that dropped to 2.75 MHz and additional low-impedance points were noted at 6.5 and 11 MHz. The patterns at 2.75 and 6.5 had the desired dipole shape, but the 11 MHz pattern had multiple lobes. Jim Bromley, K7JEB Glendale, AZ, USA |
Linear decoupling traps
Repeated message seeing that you both missed it:
73's Richard Clark, KB7QHC Hi Richard, No everything red carefully. I fully understand what you are suggesting. Cutting the element and insertin stub at right angles Sure works OK but that is no answer to my original question, HI 73 Jouko OH5RM |
Linear decoupling traps
wrote in message ... HI Theory says that whatever condition exists at far end of 1/4 wave stub will appear at fed end. ie. if far end is left open a high impedance will appear at fed end, at resonant freq. So it would appear that the shorted end should be nearest to feed point of antenna. The centre of dipole or bottom of a vertical. Hope that makes sense!................................Rod EI3CZ You have it just backwards. A 1/4 wave stub is an impedance converter. i.e. a short at one end appears as an open at the other end. Dale W4OP |
Linear decoupling traps
On Wed, 16 Apr 2008 09:36:27 -0500, Cecil Moore
wrote: Is 24 dBi omnidirectional gain from a vertical antenna enough to "get hyperbolic about trivialities"? Hysterical AND hyperbolic apparently. |
Linear decoupling traps
On Wed, 16 Apr 2008 19:50:18 +0300, "JN" wrote:
Repeated message seeing that you both missed it: 73's Richard Clark, KB7QHC Hi Richard, No everything red carefully. I fully understand what you are suggesting. Cutting the element and insertin stub at right angles Sure works OK but that is no answer to my original question, HI Your original question: My question: Is there any difference if the shorted end is pointing to the center or to the tip of dipole. My specific response: Keep the line conductors at least 3, preferably more, wire diameters from the radiator or themselves. Certainly more was said, but you have shied from terse responses in the past. You have a tuned line, that is illustrated several times by you. You have a radiator, that is illustrated several times by you. You have asked about the line in proximity to the radiator several times, that is illustrated several times by you (you really need to use fixed font to do this, it is the protocol of allowing everyone to see what you mean). I have responded about the proximity of the line to the radiator several times with a very simple rule. The line going radially away from the radiator (at right angle) absolutely satisfies that rule. Keeping the line away from the radiator (at a 0 degree angle, either up or down towards a tip) can also satisfy that rule - but only if you observe the rule. If you do not observe the rule you will have problems. You may have problems even if you do - but your question lacks your requirements. So, ostensibly, yes there is a difference - this is just the nature of life. The real question is would it matter to you? Some folks worry over half a dB, others can live with -10dB. This has all been discussed to some length by others, in related topics about hairpin matches. A general reading of the postings helps put specific problems into context and relationship. This means browse the topics that are active - not just your own. Now, do you have an original question that has gone without an answer? 73's Richard Clark, KB7QHC |
Linear decoupling traps
Here is what I mean:
http://farm3.static.flickr.com/2208/...7fd3ba40_o.jpg Measures taken from hat, but if one could say the resonance points and impedances I would be grateful Originally I asked the difference if you turn the stub 180 degrees. 73 Jouko OH5RM |
Linear decoupling traps
Jim, K7JEB wrote:
Jouko, OH5RM wrote: Take 20m of wire, that is half of a dipole. Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end is 7,25m from center and the shorted end pointing to the tip of antenna. One side of stub is the 20m wire itself, like in the upper picture. I did just that with EZNEC, but with a free-space dipole. Without the stubs, the antenna resonated at 3.6 MHz. With the stubs, that dropped to 2.75 MHz and additional low-impedance points were noted at 6.5 and 11 MHz. The patterns at 2.75 and 6.5 had the desired dipole shape, but the 11 MHz pattern had multiple lobes. Great minds think alike. :-) I was doing the same thing at different frequencies. I noticed that a 1/2WL dipole with 1/4WL stubs on each end tends to resonate on frequencies in a ratio of about 2.57:1. 18.14/2.57=7.06 so such an antenna should be resonant on both 17m and 40m. EZNEC agrees. Here are the approximate dimensions for the dualband 40m/17m antenna. Cutting and trying will be necessary for fine tuning to resonance. Note that the antenna is about 13 feet shorter than a 1/2WL dipole on 40m. It has a dipole pattern on both 40m and 17m and a 50 ohm SWR less than 2:1 on both bands. It appears to be linear-loaded on 40m and stub-matched on 17m. 26.8' 26.8' +-------------------------FP-------------------------+ | | +------------ ------------+ 13.3' 13.3' Since 10.125/2.57=3.9 MHz, this antenna should be scalable to become a dualbander on 75m and 30m. -- 73, Cecil http://www.w5dxp.com |
Linear decoupling traps
On Wed, 16 Apr 2008 21:53:39 +0300, "JN" wrote:
Here is what I mean: http://farm3.static.flickr.com/2208/...7fd3ba40_o.jpg Measures taken from hat, but if one could say the resonance points and impedances I would be grateful Originally I asked the difference if you turn the stub 180 degrees. Hi Jouko, If we are looking at four wire segments to the left of the center of the dipole, then this is a lattin design element. All my comments about that stand. As for speculating where it resonates, there is not enough dimensioning to be exact (while there is little enough to make a poor guess). I would only ask, do you want it to act as a trap such that the radiating portion of the antenna is confined to the right (as illustrated in your link) of this construction (like a conventional trap for a dual band operation)? Or do you want the element to act as linear loading to make the entire structure resonate at a shorter physical length? If you turn the element, yes, it will make a difference. There is still a long road to travel to make it "work" and it probably won't look like your link's illustration and it won't resonate where you expect it to. You still have to observe the separation of the two lines by at least 3 times the largest diameter wire/rod. 73's Richard Clark, KB7QHC |
Linear decoupling traps
"JN" wrote in message ... I thought Richard's statement that modeling would tell you about how the design might perform, was good advice. If you use EZNEC, I'd be willing to help you if you dont already know how to use it to model your antenna. Jerry KD6JDJ Jerry, thanks for the offert. I dont know how good these modelling programs are in this situation. But if it is easy, so could somebody do the following: Take 20m of wire, that is half of a dipole. Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end is 7,25m from center and the shorted end pointing to the tip of antenna. One side of stub is the 20m wire itself, like in the upper picture. Ignore all velocity factors to make it sinple. Now tell me what are the resonance frequencies of that kind of element and if possible feed point impedande (80m and 30m) I know I could do it myself but as you know learning to use a new program reliably takes lot of time. 73 Jouko OH5RM Hi Jouko I suspect that you either understimate your ability to learn or you arent aware of how EZNEC works. I submit to you that a modeling program is the best method of establishing the antenna design you are describing. You can probably learn everything you need to know about your antenna within a few hours of thinking on your own. You dont need to attend a class room course on use of the EZNEC program. I considered computer modeling to be beyond my ability till Richard Clark encouraged me to 'just try it'. I tried it, and I consider the program to be the best tool a HAM could have for developing antennas. I am sure you will figure out how to model your "trap" antenna and learn how well it will work for you within a very short time. You even have access to some EZNEC experts from this rraa group. Try it, you'll like it. Jerry KD6JDJ |
Linear decoupling traps
After a bit of e-mail correspondence and the
exchange of a single, crucial, 1000-word, picture, I think we've bottomed-out on this. I'm seeing two, distinct, dipole-like responses, one at 3.6 MHz and one at 10.2 MHz. The EZNEC outputs and source file are at: http://www.arizona-am.net/test/Antenna_Stubs_SWR.pdf http://www.arizona-am.net/test/Anten...bs_picture.pdf http://www.arizona-am.net/test/Anten..._10MHz_SWR.pdf http://www.arizona-am.net/test/Anten...s_3MHz_SWR.pdf http://www.arizona-am.net/test/Antenna_Stubs_wires.pdf http://www.arizona-am.net/test/Antenna_Stubs_Patt.pdf http://www.arizona-am.net/test/Ant_End_Stubs.EZ Jim, K7JEB |
Linear decoupling traps
Jim, K7JEB wrote:
After a bit of e-mail correspondence and the exchange of a single, crucial, 1000-word, picture, I think we've bottomed-out on this. I'm seeing two, distinct, dipole-like responses, one at 3.6 MHz and one at 10.2 MHz. 10.2/3.6=2.8 It appears that frequency ratios between about 2.4 and 2.8 can be easily achieved. That's 75m+30m, 40m+17m, 30m+12m. Unfortunately, a 2:1 ratio seems difficult to achieve. -- 73, Cecil http://www.w5dxp.com |
Linear decoupling traps
Unfortunately, a 2:1 ratio seems difficult to
achieve. -- 73, Cecil http://www.w5dxp.com In real life, at least in my case the stub will be made of twin-lead type material which shortens it abt 30%. If the shortening effect at lower frequency due to the inductive loading of stub is less, then it would be possible. Going one step further you could easily add another band to the design as parallell dipole for 17m using unused parts of douple-line. That should have litle interaction to the original double band antenna. http://farm4.static.flickr.com/3016/...fd3b1e6c_o.jpg As Jim K7JEB verified, the total half length is not 20m but 15,5m due to the loading effect of the stub. The real stub length is 1/4 WL at higher frequency respecting the velocity factor of material used. 73 Jouko OH5RM |
Linear decoupling traps
On 16-Apr-2008, "Jim, K7JEB" wrote: After a bit of e-mail correspondence and the exchange of a single, crucial, 1000-word, picture, I think we've bottomed-out on this. I'm seeing two, distinct, dipole-like responses, one at 3.6 MHz and one at 10.2 MHz. I also played around with this yesterday on EZNEC. Started with a 75 M center fed half wave at 30 feet high, added 20 M quarter wave stubs one quarter wave (20 M) oout from the center. Got two low SWR points at ~3.5 MHz and ~14 MHz. By changing the distances to the stubs, the length of the stubs, and the length beyond the stubs, I got the low SWR points to 3.9MHz (2.8:1) and 14.2 MHz (1.2:1). Azimuth pattern on 14.2 MHz was sort of omni-directional with major lobes at 45, 135, 225, and 315 degrees. Pattern on 75 M was omnidirectional at high angles and max gain straight up. Conclusions: Might be useful as a way to add 20 Meters to a shortened 75 M dipole. High SWR on 75 would still require a tuner. Losses were not determined. More height might help. Ken Fowler, KO6NO |
Linear decoupling traps
Ken Fowler wrote:
I also played around with this yesterday on EZNEC. Started with a 75 M center fed half wave at 30 feet high, added 20 M quarter wave stubs one quarter wave (20 M) oout from the center. That's a conventional trapped dipole with stub traps instead of LC traps. Here's a graphic from my web page: http://www.w5dxp.com/eznec.gif -- 73, Cecil http://www.w5dxp.com |
Linear decoupling traps
On Wed, 16 Apr 2008 09:48:34 -0700, "Jim, K7JEB"
wrote: Jouko, OH5RM wrote: Take 20m of wire, that is half of a dipole. Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end is 7,25m from center and the shorted end pointing to the tip of antenna. One side of stub is the 20m wire itself, like in the upper picture. I did just that with EZNEC, but with a free-space dipole. Without the stubs, the antenna resonated at 3.6 MHz. With the stubs, that dropped to 2.75 MHz and additional low-impedance points were noted at 6.5 and 11 MHz. The patterns at 2.75 and 6.5 had the desired dipole shape, but the 11 MHz pattern had multiple lobes. Jim Bromley, K7JEB Glendale, AZ, USA I only have EZNEC 3 and the EZNEC 4 demo. I don't remember the dimensions, but I remember that in the instructions, EZNEC could not make accurate measurements with parallel wires within a certain distance like 8-10 inches. (someone correct me here.) holding that assumption... I have not modeled that antenna or made one, but I had an experience with an 80 meter dipole that may relate. I cut a wire way too long for 80 meters, I think it was something like 140 feet or so. I use insulated stranded copper wire so I tried folding back the ends until I shortened the antenna to 75 meters. What I discovered was, that the change in frequency of the antenna did not match the reduced length of the wire. After trying for quite some time, even after measuring the antenna, I found it physically shorter than the calculated length, but the center frequency, which changed a little, hadn't changed significantly as expected. My conclusion was that I basically made a linear-loaded dipole and the total electrical length of the antenna was basically the wire length minus a small amount for interaction between the folded back wire and the original leg. It wasn't until I trimmed the wire itself that I raised the frequency of the antenna. The wire I used had the ends loosely wrapped around the main wire of the dipole, not tightly wrapped like the turns on a hangman's noose. It was insulated THHN stranded copper. Let's look at the 40/80 meter antenna cut for the CW portions (3.5 & 7 MHz). Assume, for the sake of argument that the 468/f = length in feet accounts for the velocity factor and that it is the same for the 40 meter portion as the whole wire... In theory, the Lattin antenna should be a total of 133.7 feet long, with 66.85 (1/2) of the total length being the 40 meter wire and 1/2 on each end being the 40 meter decoupling trap. Overall there is a total length of 200 feet of wire which theoretically would give you 40 and 80 meters. UNLESS the RF reacts according to my experience above which would produce an antenna which would be tuned for 7.0 and 2.3 MHz (give or take reaction) If this is true, and even with the reaction, the 40 meter dipole would work, but you couldn't make the Lattin antenna work with the those two bands. I might assume that 30 and 80 meters would work as the total length of the 30 meter portion with trap would be less than 133 feet and the 80 meter dipole would extend past the trap as an additional extension of wire. Presumeably, that antenna would be resonant on 30 meters, 80 meters and somewhere else, maybe close to 6 or 7 mhz (Total length of the wire from feed to end of trap.) -------------------------------------------------------- O -------... 3.5 MHz | 10 Mhz __________ trap plus ? Mhz I don't know how the diagram shows, I hope you get an understanding of what I am saying. Comments? ===================== PS, after writing all that, I re-read your post more carefully. I think your EZNEC model reflected what i said all along. The difference being that the continuation of the 80 meter dipole element seems to be overlooked by EZNEC. (ok, done this time :) -- 73 for now Buck, N4PGW www.lumpuckeroo.com "Small - broadband - efficient: pick any two." |
Linear decoupling traps, FINAL PLAN
"JN" wrote in message ... I am planning a two band antenna for 30 and 80m using linear traps. The idea is to build the antenna of zip-cord type line 140ohm vf 0.73. Trap is made using 1/4 wave shorted stub, decoupling occurs at the open end. Thanks to everybody for valuable comments. Special thanks to Jim K7JEB, who made the simulation and verified that the antenna works as expected. After much confusion with the text graphics, I learned the lesson to never use them again So here is how the antenna works http://farm4.static.flickr.com/3078/...7c03acc4_o.jpg I am going to use this kind of material, which is very commonly used by telephone companies here. http://www.saunalahti.fi/hohtola/ham/killu/killu.html And here is how it will be made: http://farm3.static.flickr.com/2072/...5653e9b9_o.jpg Why not normal traps? Easier to build Why not parallell dipoles? Much shorter You get three bands if needed very easily 73 Jouko OH5RM |
Linear decoupling traps
Buck wrote:
. . . I don't remember the dimensions, but I remember that in the instructions, EZNEC could not make accurate measurements with parallel wires within a certain distance like 8-10 inches. (someone correct me here.) . . . That's not correct. However, it is essential to align the segment junctions so they're directly across from each other when modeling closely spaced parallel wires. Roy Lewallen, W7EL |
Linear decoupling traps
"Roy Lewallen" wrote in message news:VfidnZbNEK-reZXVnZ2dnUVZ_tHinZ2d@easystreetonline... Buck wrote: . . . I don't remember the dimensions, but I remember that in the instructions, EZNEC could not make accurate measurements with parallel wires within a certain distance like 8-10 inches. (someone correct me here.) . . . That's not correct. However, it is essential to align the segment junctions so they're directly across from each other when modeling closely spaced parallel wires. Roy Lewallen, W7EL Roy, One question: Down the list is my posting FINAL PLAN. Is it possible with EZNEC to simulate it? It is made of transmission line (partly) Yes or No is enough. I have the DEMO version. 73 Jouko OH5RM |
Linear decoupling traps
JN wrote:
Roy, One question: Down the list is my posting FINAL PLAN. Is it possible with EZNEC to simulate it? It is made of transmission line (partly) Yes or No is enough. I have the DEMO version. 73 Jouko OH5RM Yes, a simulation should be reasonably accurate. The segmentation limitation of the demo version will probably reduce the accuracy some, but you'll be able to get a very good idea of how it will work. Roy Lewallen, W7EL |
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