|
using coax shield to create a loading coil ?
Good morning. I would like to experiment with making a high Q coil for creating
a tuned radial counterpoise. Reg's program predicts a coil of about 70 uH will create a match. One way to create such a coil would be to wind coax and use the shield as the conductor. Besides the obvious loss of physical stability due to lack of a form what are the limitations or drawbacks from using the shield? Thanks - Dan - kb0qil |
using coax shield to create a loading coil ?
dansawyeror wrote:
Good morning. I would like to experiment with making a high Q coil for creating a tuned radial counterpoise. Reg's program predicts a coil of about 70 uH will create a match. One way to create such a coil would be to wind coax and use the shield as the conductor. Besides the obvious loss of physical stability due to lack of a form what are the limitations or drawbacks from using the shield? The braided shield will be substantially lossier than a solid wire or tube of the same diameter. And the relatively poor quality dielectric used for the outside of the cable will also reduce the Q somewhat. So coax isn't a good choice for your stated objective of making a high Q coil. Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
The braided shield will be substantially lossier than a solid wire or
tube of the same diameter. Why? And the relatively poor quality dielectric used for the outside of the cable will also reduce the Q somewhat. The sheath is easy to strip. |
using coax shield to create a loading coil ?
Mike Speed wrote:
The braided shield will be substantially lossier than a solid wire or tube of the same diameter. Why? Two factors. One is surface roughness. The other is caused by the current having to continually move from one group of wires to another as it travels. I'm just now doing some research on how significant these effects are, but so far I've found out they're very noticeable. It's one of the reasons the loss of typical coax is substantially greater than predicted with idealized programs or calculations that fail to take these factors into effect. And the relatively poor quality dielectric used for the outside of the cable will also reduce the Q somewhat. The sheath is easy to strip. True enough, but my guess is that the resulting water and crud you'll be getting among the fine wires will be worse than the insulation. But hey, you don't have to believe me. Make up some coils and measure their Q -- it's not hard at all. Then stick them outside for a while and measure them again. Or do like most amateurs do -- make the coils, discover that you can talk to far away places "barefoot", and declare that they "work". Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
Two factors. One is surface roughness. The other is caused by the current having to continually move from one group of wires to another as it travels. Interesting, but how do you know the current is moving as you say? I'm just now doing some research on how significant these effects are, but so far I've found out they're very noticeable. Ok. I'm curious: What equipment are you using for the research? But hey, you don't have to believe me. Make up some coils and measure their Q -- it's not hard at all. Then stick them outside for a while and measure them again. What would be a good way to measure Q? Or do like most amateurs do -- make the coils, discover that you can talk to far away places "barefoot", and declare that they "work". Uugghh, don't I know. |
using coax shield to create a loading coil ?
You may have better luck by using sone soft copper tubing. Dimensional
stability would be one advantage. You could use ScotchKote or some insulating paint if you needed it to be insulated. "dansawyeror" wrote in message ... Good morning. I would like to experiment with making a high Q coil for creating a tuned radial counterpoise. Reg's program predicts a coil of about 70 uH will create a match. One way to create such a coil would be to wind coax and use the shield as the conductor. Besides the obvious loss of physical stability due to lack of a form what are the limitations or drawbacks from using the shield? Thanks - Dan - kb0qil |
using coax shield to create a loading coil ?
Mike Speed wrote:
Two factors. One is surface roughness. The other is caused by the current having to continually move from one group of wires to another as it travels. Interesting, but how do you know the current is moving as you say? Skin effect is well known. On a good conductor at high frequencies, current is concentrated very near the surface. When a bundle of wires ducks under another in the direction of current flow, the current has to migrate to the outside again, which means it has to move from one conductor to another. There's no question that it happens -- what's a bit harder to pin down is just how much loss typically results. I'm just now doing some research on how significant these effects are, but so far I've found out they're very noticeable. Ok. I'm curious: What equipment are you using for the research? Books, and to a lesser extent the web. Information about this is scattered among a number of sources. Quite a few discuss surface roughness in a general way, but there's a particularly good explanation, analysis, and something of a quantitative treatment in Johnson & Graham's _High-Speed Signal Propagation: Advanced Black Magic_. The effect of weaving is harder to track down -- most authors simply assume coax shield conductivity loss to be negligible, and don't deal with woven conductors in any other context. But it really isn't, if you're interested in good accuracy. And of course when the braided conductor is the primary conductor, it becomes much more important. I know Tom, W8JI has done some measurements on braided vs solid strap, and I'll be asking him for more information before long. I do know that he found a very significant difference, and I have a great deal of respect for his experience, measurements, and opinions. But hey, you don't have to believe me. Make up some coils and measure their Q -- it's not hard at all. Then stick them outside for a while and measure them again. What would be a good way to measure Q? The way I do it is by resonating the inductor with a parallel air variable capacitor. It's important to keep it away from just about everything. I couple in and out with a very small (typically 1 pF at HF) capacitor, and make sure that the impedances of the source and detector are either very high or quite low (say 50 ohms) to minimize loss. I use a signal generator for the source and a scope for the detector. Using a frequency counter connected to the signal generator, I measure the resonant frequency and -3dB points. The Q is the ratio of the center frequency to the 3dB bandwidth. For convenience, I made a 3dB pad I can switch in an out of the signal generator. With this, you don't even need a linear detector, and a diode and meter would do. My measurements have been within about 5 - 10% of readings with a good HP Q meter on the few occasions when I've compared them. That's close enough for my purposes. Or do like most amateurs do -- make the coils, discover that you can talk to far away places "barefoot", and declare that they "work". Uugghh, don't I know. Many people have worked the world with 1 watt, knowing that's what they were running. A lot more have worked the world with 1 watt, thinking they were running 100. Ignorance is bliss. Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
Roy,
Thank you. It is a quick experiment to build a test coax coil and measure the Q. That should produce enough evidence to test a counterpoise. In the mean time the research to build a coil out of copper tubing continues. So far the only alternative I can conceive is to make a wooden form and wrap the coil on the outside. Thanks again - Dan Roy Lewallen wrote: Mike Speed wrote: Two factors. One is surface roughness. The other is caused by the current having to continually move from one group of wires to another as it travels. Interesting, but how do you know the current is moving as you say? Skin effect is well known. On a good conductor at high frequencies, current is concentrated very near the surface. When a bundle of wires ducks under another in the direction of current flow, the current has to migrate to the outside again, which means it has to move from one conductor to another. There's no question that it happens -- what's a bit harder to pin down is just how much loss typically results. I'm just now doing some research on how significant these effects are, but so far I've found out they're very noticeable. Ok. I'm curious: What equipment are you using for the research? Books, and to a lesser extent the web. Information about this is scattered among a number of sources. Quite a few discuss surface roughness in a general way, but there's a particularly good explanation, analysis, and something of a quantitative treatment in Johnson & Graham's _High-Speed Signal Propagation: Advanced Black Magic_. The effect of weaving is harder to track down -- most authors simply assume coax shield conductivity loss to be negligible, and don't deal with woven conductors in any other context. But it really isn't, if you're interested in good accuracy. And of course when the braided conductor is the primary conductor, it becomes much more important. I know Tom, W8JI has done some measurements on braided vs solid strap, and I'll be asking him for more information before long. I do know that he found a very significant difference, and I have a great deal of respect for his experience, measurements, and opinions. But hey, you don't have to believe me. Make up some coils and measure their Q -- it's not hard at all. Then stick them outside for a while and measure them again. What would be a good way to measure Q? The way I do it is by resonating the inductor with a parallel air variable capacitor. It's important to keep it away from just about everything. I couple in and out with a very small (typically 1 pF at HF) capacitor, and make sure that the impedances of the source and detector are either very high or quite low (say 50 ohms) to minimize loss. I use a signal generator for the source and a scope for the detector. Using a frequency counter connected to the signal generator, I measure the resonant frequency and -3dB points. The Q is the ratio of the center frequency to the 3dB bandwidth. For convenience, I made a 3dB pad I can switch in an out of the signal generator. With this, you don't even need a linear detector, and a diode and meter would do. My measurements have been within about 5 - 10% of readings with a good HP Q meter on the few occasions when I've compared them. That's close enough for my purposes. Or do like most amateurs do -- make the coils, discover that you can talk to far away places "barefoot", and declare that they "work". Uugghh, don't I know. Many people have worked the world with 1 watt, knowing that's what they were running. A lot more have worked the world with 1 watt, thinking they were running 100. Ignorance is bliss. Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
On Fri, 17 Feb 2006 17:25:28 -0800, Roy Lewallen
wrote: ... Or do like most amateurs do -- make the coils, discover that you can talk to far away places "barefoot", and declare that they "work". Roy, As we dumb amateur radio down to make it attractive to the disinterested masses in a desperate and mistaken persuit of increasing the number of licenced hams, this is becoming the new standard of understanding in the redefined amateur radio. I wrote comment on an a recent article in Australia's ham radio magazine "Amateur Radio" that was an example of the declaration of not just something that works, but "something that really works" though it looks to be quite inefficient on at least one band. The comment is at http://www.vk1od.net/blog/index.php?...Id=21&blogId=1 .. Supporters argue "amateur radio is about having QSOs, so if you have QSOs then the antenna works... QED". Though antenna systems remains one of the few areas of amateur radio where hams can cost effectively design solutions specific to their location and needs, the lower competency standard of the new "communicator" style amateur does not support a soundly based understanding of antenna systems. We frequently hear the argument that there is no need to understand electronics for modern amateur radio where commercial radios are the norm, but forget electronics for a moment, how many hams understand a common three component passive network that is so often employed with variable results, the ATU. Get used to it! Amateur radio is being transformed to "I just wanna talk on the radio". Owen -- |
using coax shield to create a loading coil ?
When a bundle of wires ducks under another in the direction of current flow, the current has to migrate to the outside again, snip
There's no question that it happens Books, and to a lesser extent the web. Information about this is snip I have a great deal of respect for his experience, measurements, and opinions Again, interesting, but what's been outlined so far is not scientific. For something of this nature to be of any utility, it must be grounded in science. |
using coax shield to create a loading coil ?
Mike Speed wrote:
Roy Lewallen had written: When a bundle of wires ducks under another in the direction of current flow, the current has to migrate to the outside again, snip There's no question that it happens Books, and to a lesser extent the web. Information about this is snip I have a great deal of respect for his experience, measurements, and opinions Again, interesting, but what's been outlined so far is not scientific. For something of this nature to be of any utility, it must be grounded in science. The skin effect is most thoroughly grounded in science. What you seem to be unaware of is that it's *so* well-known that, in any discussion about RF engineering, the scientific proof of its existence can be 'taken as read'. For a detailed scientific proof of the skin effect, try: http://tinyurl.com/brpq6 That proof is more general - and hence more powerful - than the ones you find in most engineering texts such as Terman. It demonstrates that, if an RF current is flowing across *any* conducting surface (not restricted to any particular shape or cross-section) and also for *any reason* (not limited to any particular kind of circuit or device) then there will be a skin effect. That's the science of it; now back to the engineering. What Roy said was quite correct. Braid is a kind of composite conducting surface, made up of the exposed surfaces of the individual strands. The skin effect means that the outside of the composite surface must always carry the highest RF current density (amperes per square micron of cross-sectional area). So whenever the weave of the braid makes an exposed strand dive below the surface, the RF current must cross over to the next touching strand that is still exposed. A little way further along the braid, it will have to cross over again... and again, and again. It is hard to visualize exactly how these crossovers happen on a microscopic scale, but the physics of the skin effect dictate that it *must* happen somehow. Obviously physical and electrical contact between the two strands is required. We also know that electrical contact works better when there is a strong force pushing the two conductors together, because the force deforms the two surfaces into each other, to give a greater contact area. The key fact is that the contact forces between strands in a braid are very small and unreliable. That means the RF resistance of a length of braid will be significantly higher than for a smooth conductor with the same external surface area. Then it gets worse. Even the thinnest film of corrosion can disrupt the contact between copper strands in a braid. Unless the current density is large enough to break down this film, it means the RF current is forced to flow into the interior of the braid. Again the exact geometry is hard to visualize, but again the physics dictate that if an isolated 'filament' of current is forced to flow beneath a conducting surface, the voltage drop per unit length must increase - in other words, the RF resistance must increase. Scientific deduction has told us that all these effects must exist. Whatit cannot tell us is how big they are in real braid, or how important they are in practice. For that we'll need some measured numbers. You have two choices he either look for existing measurements from people who have demonstrated their competence and scientific approach; or do it yourself. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
using coax shield to create a loading coil ?
Mike, leakage and inductive and gap effects in woven braid has been in
the science literature for over 40 years. To keep this discussion focused I have emailed one specific reference to Roy. Hopefully Roy has the time and resources to do the research and make the results available to us in terms we can understand. Mike Speed wrote: When a bundle of wires ducks under another in the direction of current flow, the current has to migrate to the outside again, snip There's no question that it happens Books, and to a lesser extent the web. Information about this is snip I have a great deal of respect for his experience, measurements, and opinions Again, interesting, but what's been outlined so far is not scientific. For something of this nature to be of any utility, it must be grounded in science. |
using coax shield to create a loading coil ?
dansawyeror wrote:
Roy, Thank you. It is a quick experiment to build a test coax coil and measure the Q. That should produce enough evidence to test a counterpoise. In the mean time the research to build a coil out of copper tubing continues. So far the only alternative I can conceive is to make a wooden form and wrap the coil on the outside. Thanks again - Dan A copper tube will definitely produce an improved Q. If you do make comparative measurements of ones made from tubing and from coax, please post the results. A real problem in maintaining the Q of coils outside in the weather is keeping water from getting between the turns. Water is very lossy stuff at HF, and it has a very high dielectric constant. The two combine to make it a real Q killer if it gets into any region of high electric field strength. A bit of accumulated dust mixed with the water makes it worse yet. So if you anticipate leaving the coil on a form and exposed to the weather, also check the Q when the coil is wet. See http://www.eznec.com/Amateur/Article...Feed_Lines.pdf for results of measurements of wet and dry 300 ohm twin lead. It's not quite the same situation, but the loss mechanism is essentially the same. I recommend that you do some modeling or just simple calculating, if you haven't done so already, to see just how high the Q has to be in order to keep overall loss acceptable. One final thing to keep in mind -- I've heard reports of poor performance of elevated verticals being tracked down to badly imbalanced currents in the radials. Apparently even small physical differences among the radials can cause one or two to hog all the current. If this is so, it seems to me that making them more sharply tuned by inductive loading might make this effect even worse. So when you get the thing up, I suggest measuring the current in each radial. This is easily done with a toroid core with a few turns for the secondary and a fairly low R across the secondary. It's been discussed a number of times on this newsgroup, the last time quite recently. Good luck! Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
Mike Speed wrote:
Again, interesting, but what's been outlined so far is not scientific. For something of this nature to be of any utility, it must be grounded in science. I can assure the readers that all the effects I've discussed are soundly based on very well known principles. Anyone truly interested in the topic can find ample confirmation of what I've said, although it might take a bit of digging. The Johnson and Graham text is an excellent place to start. What's lacking is good measured data for typical shields, and even that's going to have limitations because of the wide variations among cables and manufacturers. But even some rules of thumb will be useful. But you've shown an interest in the topic. Why don't you make some measurements of coils made from tubing and from coax shields and report back? Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
Just my 29 cents worth... I don't think using real thick
copper tube, coax shield, etc, will really be worth the trouble, vs using a standard wire wound coil on a form. There is some increase in performance , but overall it will be fairly small unless the wire used in the standard coil is very thin. Once you get to about 1mm thickness, you will have fairly decent performance. 2mm is even better, and any increase using a thick tubing will basically be a waste of time. I think anyway... The spacing of the wires, and keeping water, etc from between the coil windings is more important. You can wind a coil using 14 gauge wire and have a very high Q coil, if wound right. Even 18 or 16 gauge won't be too bad as long as there is the proper spacing between windings. Again, just my opinion from building various mobile antenna coils... I'm pretty picky about my mobile antennas, but I don't bother using "fat" coil conductors. To me, not worth the extra trouble, weight, etc. I don't think the extra performance is that great vs any regular wound coil , that has the proper pitch. With the thinner wire coils, it's using a close winding pitch, with the wires nearly touching that makes for excess loss. Not really the thin wire in itself unless it's super thin like magnet wire. And yes, I avoid braid for anything carrying rf. Even my grounding straps are solid. MK |
using coax shield to create a loading coil ?
Roy Lewallen wrote:
SNIPPED What's lacking is good measured data for typical shields, and even that's going to have limitations because of the wide variations among cables and manufacturers. But even some rules of thumb will be useful. But you've shown an interest in the topic. Why don't you make some measurements of coils made from tubing and from coax shields and report back? Roy Lewallen, W7EL I've been away from that measurement field [integrity of coaxial braid shields] for almost 15 years. Measured data does exist for the effects of shield parameters [weave angle, optical coverage, # strands {picks}, wire gauge, etc.] based on using traveling wave excitation of the braid itself in either quadraxial test fixtures or over a controlled ground plane with known Zo between the cable and the plane. Test methods are IEEE defined [after 15+ years I can't recall a specific IEEE Test Method reference]. These quantify a 'leakage inductance'. |
using coax shield to create a loading coil ?
On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror
wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Hm. Just searched the FCC database for a SPEED, MI... and nothing pops.
QRZ.COM gives quite a few (39) hits for SPEED, but none with the first name or middle initial that you can make a "mike" from. Hm. Jim "Mike Speed" wrote in message oups.com... |
using coax shield to create a loading coil ?
A visit to the kitchen supplies of your local department store will
reveal a large assortment of coil forms and covers. Until recently I have limited my antenna work to vhf-uhf. In that circumstance I have frequently punched a snug hole in a plastic container bottom and placed it in a bell shaped fashion over lumped LC components. It has worked best for me to leave the bottom open for ventilation. I have not done it yet but preliminary plans for a base loaded 160 meter vertical have me considering an inverted plastic garbage can as a weather shield. The EZNEC models may spare me the effort on that one! On Sat, 18 Feb 2006 06:26:14 -0800, Roy Lewallen wrote: dansawyeror wrote: Roy, Thank you. It is a quick experiment to build a test coax coil and measure the Q. That should produce enough evidence to test a counterpoise. In the mean time the research to build a coil out of copper tubing continues. So far the only alternative I can conceive is to make a wooden form and wrap the coil on the outside. John Ferrell W8CCW |
using coax shield to create a loading coil ?
"Roy Lewallen" wrote I can assure the readers that all the effects I've discussed are soundly based on very well known principles. ==================================== Roy, you seem to have forgotten proximity effect. If one calculates the Q of a coil from HF skin resistance of the wire and from coil inductance, one gets ridiculously high values of Q. Other producers of coil calculators appear to have forgotten this too. That's if they were ever aware of it. I have a coil, about 4 inches long, about 1.7 inches in diameter, with about 90 close-wound turns of 1mm diameter wire, which has an inductance of about 100 micro-henrys. The measured value of Q at 1.9 MHz is about 240. This makes the proximity effect about 3.5 or 4 times the effect of simple HF wire skin resistance. This is a large amount. This is the first time such information has been appeared on a newsgroup or published in bibles anywhere else. They didn't have Q meters 120 years ago, in Heaviside's time, when such factors were first considered. My findings are incorporated in program SOLNOID3 which estimates Q (and other characteristics) for coils of various dimensions. There are, of course, other factors which influence Q which is a relatively unimportant coil characteristic. What do you do with Q once you have taken the trouble to find it? The other more important things will already be apparent. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
using coax shield to create a loading coil ?
To extend from Ian's remarks:
In some critical applications, the use of coax cable with braided outer Cu conductor can cause problems. RF charge flow (current) in the braid experiences a non-linear circuit resulting in harmonic distortion or IM or both. Just made coax can have a very low level of non-linearity with the effect increasing with age (and probable corrosion). Ag plated Cu braid seems to have less of the non-linear effect - perhaps because of a poorer mechanism for current to move from one wire to another. The effects are small, but can be important in certain applications. Solid Cu outer conductors have advantages beyond mechanical and power-handling. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Ian White GM3SEK" wrote in message snip Then it gets worse. Even the thinnest film of corrosion can disrupt the contact between copper strands in a braid. Unless the current density is large enough to break down this film, it means the RF current is forced to flow into the interior of the braid. Again the exact geometry is hard to visualize, but again the physics dictate that if an isolated 'filament' of current is forced to flow beneath a conducting surface, the voltage drop per unit length must increase - in other words, the RF resistance must increase. Scientific deduction has told us that all these effects must exist. Whatit cannot tell us is how big they are in real braid, or how important they are in practice. For that we'll need some measured numbers. You have two choices he either look for existing measurements from people who have demonstrated their competence and scientific approach; or do it yourself. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
using coax shield to create a loading coil ?
These results were from Reg's c_poise program. The band is 75 meters and the
coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Q meters, above the range of 150, fall into the same category as so
called SWR meters above the range of 1.5 Neither are of much use. Just an opinion! ---- Reg. |
using coax shield to create a loading coil ?
May I suggest the use of PVC pipe as a form for winding the
coax? Tape it in place while you're "monkeying" and then fiberglass it when you like what you have. (Auto supply stores sell the fiberglass for doing auto body work -- it's durable & light-weight.) KD6VKW ET USN (ret) That sounds like a good idea - and I have used pvc forms myself. I wonder if ecasing the coil in that 'Great Stuff' spray foam would be ample protection ? my 2¢ W4PMJ |
using coax shield to create a loading coil ?
These results were from Reg's c_poise program. The band is 75 meters and the
coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. I haven't tried that program, so don't know what it's for... But... 70 uh is not far off from the usual inductance needed to match a 80m mobile antenna. When using Reg's "vertload" program, which I use for designing mobiles, I don't see near the spread of coil loss that you see in that program. In vertload, to make that large a coil using 12 mm wire, the coil diameter has to be fairly large just to be able to fit enough turns in the appx 12 inch height I allowed for the coil. But when comparing a like coil using 1 mm wire, and the same coil using 12 mm wire, I only saw about 1 ohm difference, not 5. I'm not sure which is the most accurate, but so far my real world results in mobile whips seems to jive pretty well with vertload. I've made a few coils with pretty thin wire, and had good results as long as the turn ratio was ok. Ditto for fatter wire coils. I made one that was 12 gauge and could see only a small difference from one made with 16 gauge wire. Seemed to shrink my bandwidth very slightly. So...Dunno..Would have to do some tests to get the real lowdown on the differences in loss I guess. But with the mobiles, I came to the conclusion that real thick wire was not really needed for a good coil, as long as the winding ratio was right. MK |
using coax shield to create a loading coil ?
Frank,
Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Frank,
Thanks for the model. I did not expect you to model this or I would have been more specific. The antenna is about 14 feet. The coil is about 4 feet from the base. Now the radials: Did you base the radial from Reg's model? Try 3.97 MHz, 1 meter above ground, 3 meter radials, and a 60mm long by 300 mm dia 66.7 uH loading coil. These grounds have to be tuned as well. I am using 4nec2 and am getting errors from the GM card. Wasn't there an issue with these being a decimal instead of an integer? BTW - The simulation on my laptop takes over 5 minutes to run. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Follow up:
One of the not so apparent results of Reg's program is the relationship of radial length to height. I chose 2 meters because they were only .7 meters high. I raised your model to 2 meters, that reduced the R to about 20 Ohms. Raising it to 3 meters lowers it to 18 Ohms. How did you calculate the H of the loading coils? Is that easy to edit? It would seem that these values are closer. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
I see the length is set to 1.8 meters already. A 2 meter elevation minimum is
needed to lower ground effects. How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance does that translate to? How did you calculate this value? Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Dan,
I find antenna problems very interesting, so do not mind spending time on running models. The radials were based on your comments in an earlier post about "2 meter radials". You have provided me with a lot of information in subsequent posts, so will use that info to try and construct a more realistic model. I still have a couple of questions though: how many radials are you using, and where do you position the radial loading coils? You are correct about the "GM" problem, and I forgot it produced an error in 4nec2. The last "ITS" field should be an integer. I have not completely confirmed it with 4nec2, but the ITS field refers to the tag to be replicated -- in this case tag 2. GM generates 9 tags rotated by 36 degrees, and saves a ton of GW cards. I cannot understand why your simulation takes 5 minutes since there are only 184 segments, and 11 frequencies. I just checked and it takes only 3.9 seconds with my NEC2 program, or 4nec2. Anyway my model will take a lot of revision to replicate your actual antenna. May get a chance to look at it later tonight. 73, Frank "dansawyeror" wrote in message ... Frank, Thanks for the model. I did not expect you to model this or I would have been more specific. The antenna is about 14 feet. The coil is about 4 feet from the base. Now the radials: Did you base the radial from Reg's model? Try 3.97 MHz, 1 meter above ground, 3 meter radials, and a 60mm long by 300 mm dia 66.7 uH loading coil. These grounds have to be tuned as well. I am using 4nec2 and am getting errors from the GM card. Wasn't there an issue with these being a decimal instead of an integer? BTW - The simulation on my laptop takes over 5 minutes to run. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Dan, even more questions: I don't understand the relationship of radial
length to height. c_poise seems to allow anything. What is the "H" of a loading coil? Frank "dansawyeror" wrote in message ... Follow up: One of the not so apparent results of Reg's program is the relationship of radial length to height. I chose 2 meters because they were only .7 meters high. I raised your model to 2 meters, that reduced the R to about 20 Ohms. Raising it to 3 meters lowers it to 18 Ohms. How did you calculate the H of the loading coils? Is that easy to edit? It would seem that these values are closer. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Dan,
The lumped inductance of 4 +j1750 comes from your previous comment about the inductance range from 60 - 90 uH. I just chose the mid range value of 75 uH at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is based on an approximate Q of 400. Incidentaly I am working at another location this morning. The computer is an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC code here takes 17 seconds to run. 73, Frank "dansawyeror" wrote in message ... I see the length is set to 1.8 meters already. A 2 meter elevation minimum is needed to lower ground effects. How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance does that translate to? How did you calculate this value? Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Dan, here is a preliminary run on a 12 ft monopole model structured as
follows: base at 6 ft, 10 x 6ft radials. All #14 AWG. Ground - perfect, frequency 3.8 MHz. Zin = 0.968 - j1847.55 ohms; Efficiency = 87.4 % (structure copper loss); Gain = 4.15 dBi; Take-off angle = 0 deg; Gain at 27 deg elevation (expected TOA with real ground) = +3.09 dBi. I will try successive modifications to approach a practical model. The code I used, modified so it should run in 4nec2, is shown below. 73, Frank CM 75 m Vertical 12 ft high CM base 6 ft up, 10 X 6 ft radials CM copper conductivity CE GW 1 24 0 0 18 0 0 6 0.0026706 GW 2 12 0 0 6 6 0 6 0.0026706 GM 1 9 0 0 36 0 0 0 2 GS 0 0 .3048 GE 1 GN 1 EX 0 1 24 0 1.00000 0.00000 LD 5 1 1 144 5.8001E7 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN "Frank's Basement 2" wrote in message news:dhmKf.6088$_62.3050@edtnps90... Dan, The lumped inductance of 4 +j1750 comes from your previous comment about the inductance range from 60 - 90 uH. I just chose the mid range value of 75 uH at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is based on an approximate Q of 400. Incidentaly I am working at another location this morning. The computer is an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC code here takes 17 seconds to run. 73, Frank "dansawyeror" wrote in message ... I see the length is set to 1.8 meters already. A 2 meter elevation minimum is needed to lower ground effects. How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance does that translate to? How did you calculate this value? Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Frank,
Good morning. I had a few minutes and created the following model. It is shortened and the number of segments in the vertical is increased. I also set the inductors to 3 Ohms. (That may be optimistic for the antenna, Reg's program predicts 2 Ohms is achievable for larger coils on the radials.) (Sorry for the long numbers.) This shows a resonance at 3.9 MHz and 9.9 Ohms. 4nec2 did not like the GM card, I did not remove it. Dan CM 75 m Vertical 16 ft high CE GW 1 11 0 0 7.5342 0 0 2.6 8.13999e-4 GW 2 12 0 0 2.6 1.8288 0 2.6 8.13999e-4 GW 3 12 0 0 2.6 1.47953028 1.07494167 2.6 8.13999e-4 GW 4 12 0 0 2.6 0.56513028 1.73929216 2.6 8.13999e-4 GW 5 12 0 0 2.6 -0.5651303 1.73929216 2.6 8.13999e-4 GW 6 12 0 0 2.6 -1.4795303 1.07494167 2.6 8.13999e-4 GW 7 12 0 0 2.6 -1.8288 2.2396e-16 2.6 8.13999e-4 GW 8 12 0 0 2.6 -1.4795303 -1.0749417 2.6 8.13999e-4 GW 9 12 0 0 2.6 -0.5651303 -1.7392922 2.6 8.13999e-4 GW 10 12 0 0 2.6 0.56513028 -1.7392922 2.6 8.13999e-4 GW 11 12 0 0 2.6 1.47953028 -1.0749417 2.6 8.13999e-4 GE 0 LD 5 1 0 0 58001000 0 LD 4 1 7 7 3 2100 LD 4 2 1 1 3 2000 LD 4 3 1 1 3 2000 LD 4 4 1 1 3 2000 LD 4 5 1 1 3 2000 LD 4 6 1 1 3 2000 LD 4 7 1 1 3 2000 LD 4 8 1 1 3 2000 LD 4 9 1 1 3 2000 LD 4 10 1 1 3 2000 LD 4 11 1 1 3 2000 EX 0 1 11 0 1 0 GN 2 0 0 0 13 5.e-3 FR 0 1 0 0 3.5 0 EN Frank wrote: Dan, I find antenna problems very interesting, so do not mind spending time on running models. The radials were based on your comments in an earlier post about "2 meter radials". You have provided me with a lot of information in subsequent posts, so will use that info to try and construct a more realistic model. I still have a couple of questions though: how many radials are you using, and where do you position the radial loading coils? You are correct about the "GM" problem, and I forgot it produced an error in 4nec2. The last "ITS" field should be an integer. I have not completely confirmed it with 4nec2, but the ITS field refers to the tag to be replicated -- in this case tag 2. GM generates 9 tags rotated by 36 degrees, and saves a ton of GW cards. I cannot understand why your simulation takes 5 minutes since there are only 184 segments, and 11 frequencies. I just checked and it takes only 3.9 seconds with my NEC2 program, or 4nec2. Anyway my model will take a lot of revision to replicate your actual antenna. May get a chance to look at it later tonight. 73, Frank "dansawyeror" wrote in message ... Frank, Thanks for the model. I did not expect you to model this or I would have been more specific. The antenna is about 14 feet. The coil is about 4 feet from the base. Now the radials: Did you base the radial from Reg's model? Try 3.97 MHz, 1 meter above ground, 3 meter radials, and a 60mm long by 300 mm dia 66.7 uH loading coil. These grounds have to be tuned as well. I am using 4nec2 and am getting errors from the GM card. Wasn't there an issue with these being a decimal instead of an integer? BTW - The simulation on my laptop takes over 5 minutes to run. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Frank,
I tried the nec below. The result was resonant at 21.9 and about 34 Ohms. I am not competent at reading nec cards yet, however the model editor does not show any coil loads. That could explain the frequency? Dan Thanks - Dan Frank's Basement 2 wrote: Dan, here is a preliminary run on a 12 ft monopole model structured as follows: base at 6 ft, 10 x 6ft radials. All #14 AWG. Ground - perfect, frequency 3.8 MHz. Zin = 0.968 - j1847.55 ohms; Efficiency = 87.4 % (structure copper loss); Gain = 4.15 dBi; Take-off angle = 0 deg; Gain at 27 deg elevation (expected TOA with real ground) = +3.09 dBi. I will try successive modifications to approach a practical model. The code I used, modified so it should run in 4nec2, is shown below. 73, Frank CM 75 m Vertical 12 ft high CM base 6 ft up, 10 X 6 ft radials CM copper conductivity CE GW 1 24 0 0 18 0 0 6 0.0026706 GW 2 12 0 0 6 6 0 6 0.0026706 GM 1 9 0 0 36 0 0 0 2 GS 0 0 .3048 GE 1 GN 1 EX 0 1 24 0 1.00000 0.00000 LD 5 1 1 144 5.8001E7 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN "Frank's Basement 2" wrote in message news:dhmKf.6088$_62.3050@edtnps90... Dan, The lumped inductance of 4 +j1750 comes from your previous comment about the inductance range from 60 - 90 uH. I just chose the mid range value of 75 uH at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is based on an approximate Q of 400. Incidentaly I am working at another location this morning. The computer is an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC code here takes 17 seconds to run. 73, Frank "dansawyeror" wrote in message ... I see the length is set to 1.8 meters already. A 2 meter elevation minimum is needed to lower ground effects. How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance does that translate to? How did you calculate this value? Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
I missed this one. About 96 uH.
Frank's Basement 2 wrote: Dan, even more questions: I don't understand the relationship of radial length to height. c_poise seems to allow anything. What is the "H" of a loading coil? Frank "dansawyeror" wrote in message ... Follow up: One of the not so apparent results of Reg's program is the relationship of radial length to height. I chose 2 meters because they were only .7 meters high. I raised your model to 2 meters, that reduced the R to about 20 Ohms. Raising it to 3 meters lowers it to 18 Ohms. How did you calculate the H of the loading coils? Is that easy to edit? It would seem that these values are closer. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Hi Dan, I tried your program, it runs fine, and I get identical results. I
also learned a couple of things from your code: Setting "GE" = 0 implies no ground plane present (I would normally set it to "1"), and my "Nec Vu" function shows the antenna with no ground plane. Running the program, however, returns the correct result with an average ground. I also ran the program with no radial loading (code below), and the gain increased marginally. It seems loading the radials does not help much. Frank CM 75 m Vertical 16 ft high CE GW 1 11 0 0 7.5342 0 0 2.6 8.13999e-4 GW 2 12 0 0 2.6 1.8288 0 2.6 8.13999e-4 GW 3 12 0 0 2.6 1.47953028 1.07494167 2.6 8.13999e-4 GW 4 12 0 0 2.6 0.56513028 1.73929216 2.6 8.13999e-4 GW 5 12 0 0 2.6 -0.5651303 1.73929216 2.6 8.13999e-4 GW 6 12 0 0 2.6 -1.4795303 1.07494167 2.6 8.13999e-4 GW 7 12 0 0 2.6 -1.8288 2.2396e-16 2.6 8.13999e-4 GW 8 12 0 0 2.6 -1.4795303 -1.0749417 2.6 8.13999e-4 GW 9 12 0 0 2.6 -0.5651303 -1.7392922 2.6 8.13999e-4 GW 10 12 0 0 2.6 0.56513028 -1.7392922 2.6 8.13999e-4 GW 11 12 0 0 2.6 1.47953028 -1.0749417 2.6 8.13999e-4 GE 1 GN 2 0 0 0 13.0000 0.0050 LD 4 1 7 7 3 2100 LD 5 1 1 107 5.8001E7 EX 0 1 11 00 1 0 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 90 1.00000 1.00000 EN "dansawyeror" wrote in message ... Frank, Good morning. I had a few minutes and created the following model. It is shortened and the number of segments in the vertical is increased. I also set the inductors to 3 Ohms. (That may be optimistic for the antenna, Reg's program predicts 2 Ohms is achievable for larger coils on the radials.) (Sorry for the long numbers.) This shows a resonance at 3.9 MHz and 9.9 Ohms. 4nec2 did not like the GM card, I did not remove it. Dan CM 75 m Vertical 16 ft high CE GW 1 11 0 0 7.5342 0 0 2.6 8.13999e-4 GW 2 12 0 0 2.6 1.8288 0 2.6 8.13999e-4 GW 3 12 0 0 2.6 1.47953028 1.07494167 2.6 8.13999e-4 GW 4 12 0 0 2.6 0.56513028 1.73929216 2.6 8.13999e-4 GW 5 12 0 0 2.6 -0.5651303 1.73929216 2.6 8.13999e-4 GW 6 12 0 0 2.6 -1.4795303 1.07494167 2.6 8.13999e-4 GW 7 12 0 0 2.6 -1.8288 2.2396e-16 2.6 8.13999e-4 GW 8 12 0 0 2.6 -1.4795303 -1.0749417 2.6 8.13999e-4 GW 9 12 0 0 2.6 -0.5651303 -1.7392922 2.6 8.13999e-4 GW 10 12 0 0 2.6 0.56513028 -1.7392922 2.6 8.13999e-4 GW 11 12 0 0 2.6 1.47953028 -1.0749417 2.6 8.13999e-4 GE 0 LD 5 1 0 0 58001000 0 LD 4 1 7 7 3 2100 LD 4 2 1 1 3 2000 LD 4 3 1 1 3 2000 LD 4 4 1 1 3 2000 LD 4 5 1 1 3 2000 LD 4 6 1 1 3 2000 LD 4 7 1 1 3 2000 LD 4 8 1 1 3 2000 LD 4 9 1 1 3 2000 LD 4 10 1 1 3 2000 LD 4 11 1 1 3 2000 EX 0 1 11 0 1 0 GN 2 0 0 0 13 5.e-3 FR 0 1 0 0 3.5 0 EN Frank wrote: Dan, I find antenna problems very interesting, so do not mind spending time on running models. The radials were based on your comments in an earlier post about "2 meter radials". You have provided me with a lot of information in subsequent posts, so will use that info to try and construct a more realistic model. I still have a couple of questions though: how many radials are you using, and where do you position the radial loading coils? You are correct about the "GM" problem, and I forgot it produced an error in 4nec2. The last "ITS" field should be an integer. I have not completely confirmed it with 4nec2, but the ITS field refers to the tag to be replicated -- in this case tag 2. GM generates 9 tags rotated by 36 degrees, and saves a ton of GW cards. I cannot understand why your simulation takes 5 minutes since there are only 184 segments, and 11 frequencies. I just checked and it takes only 3.9 seconds with my NEC2 program, or 4nec2. Anyway my model will take a lot of revision to replicate your actual antenna. May get a chance to look at it later tonight. 73, Frank "dansawyeror" wrote in message ... Frank, Thanks for the model. I did not expect you to model this or I would have been more specific. The antenna is about 14 feet. The coil is about 4 feet from the base. Now the radials: Did you base the radial from Reg's model? Try 3.97 MHz, 1 meter above ground, 3 meter radials, and a 60mm long by 300 mm dia 66.7 uH loading coil. These grounds have to be tuned as well. I am using 4nec2 and am getting errors from the GM card. Wasn't there an issue with these being a decimal instead of an integer? BTW - The simulation on my laptop takes over 5 minutes to run. Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
using coax shield to create a loading coil ?
Reg Edwards wrote:
Roy, you seem to have forgotten proximity effect. . . . Forgotten? I just didn't see what relevance it had on the difference in Q between an inductor made from a braided coax shield and one made from solid tubing. And I can't see from your posting anything which adds to that discussion. But maybe I'm missing something? Roy Lewallen, W7EL |
using coax shield to create a loading coil ?
That's correct Dan. I just wanted to systematically build up the antenna,
adding a component at a time, to note where the major losses are. This was the first trial with no loading -- except for copper conductivity. From the other model you sent me it seems that any other attempts are redundant. The major losses are due to ground loss, as expected. Unfortunately this can only be overcome by increasing the length, and number, of radials -- something that is pretty well known. Also inductive loading of the radials does not seem to have any effect, except for marginally decreasing the antenna efficiency. I have been interested in installing a short monopole for 160m, so am very interested in your results. I have a fairly large lot (visible on "Google Earth), so am not so restricted in radial length. 73, Frank "dansawyeror" wrote in message ... Frank, I tried the nec below. The result was resonant at 21.9 and about 34 Ohms. I am not competent at reading nec cards yet, however the model editor does not show any coil loads. That could explain the frequency? Dan Thanks - Dan Frank's Basement 2 wrote: Dan, here is a preliminary run on a 12 ft monopole model structured as follows: base at 6 ft, 10 x 6ft radials. All #14 AWG. Ground - perfect, frequency 3.8 MHz. Zin = 0.968 - j1847.55 ohms; Efficiency = 87.4 % (structure copper loss); Gain = 4.15 dBi; Take-off angle = 0 deg; Gain at 27 deg elevation (expected TOA with real ground) = +3.09 dBi. I will try successive modifications to approach a practical model. The code I used, modified so it should run in 4nec2, is shown below. 73, Frank CM 75 m Vertical 12 ft high CM base 6 ft up, 10 X 6 ft radials CM copper conductivity CE GW 1 24 0 0 18 0 0 6 0.0026706 GW 2 12 0 0 6 6 0 6 0.0026706 GM 1 9 0 0 36 0 0 0 2 GS 0 0 .3048 GE 1 GN 1 EX 0 1 24 0 1.00000 0.00000 LD 5 1 1 144 5.8001E7 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN "Frank's Basement 2" wrote in message news:dhmKf.6088$_62.3050@edtnps90... Dan, The lumped inductance of 4 +j1750 comes from your previous comment about the inductance range from 60 - 90 uH. I just chose the mid range value of 75 uH at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is based on an approximate Q of 400. Incidentaly I am working at another location this morning. The computer is an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC code here takes 17 seconds to run. 73, Frank "dansawyeror" wrote in message ... I see the length is set to 1.8 meters already. A 2 meter elevation minimum is needed to lower ground effects. How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance does that translate to? How did you calculate this value? Dan Frank's Basement 2 wrote: Hi Dan, thanks for the interesting info. You did not specify dimensions, but from your comments it appears you are using a vertical about 23 ft high. Such a monopole would have a 3.5 ohm input impedance when placed above a perfectly conducting ground, and gain about +4.5 dBi. Adding a center loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi. Base loading provides an input impedance of 5.5 ohms with almost the same gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi. Adding lumped element loading coils, (75 uH, Q = 400) in each radial (antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi. Don't know why this does not agree with Reg's program. Probably I made some fundamental error with the NEC model. Included the code below, so you may see an error I missed. 73, Frank CM 75 m Vertical 23 ft high CE GW 1 64 0 0 23 0 0 0.25 0.0026706 GW 2 12 0 0 0.25 6 0 0.25 0.0026706 GM 1 9 0 0 36 0 0 0 002.002 GS 0 0 .3048 GE 1 GN 2 0 0 0 13.0000 0.0050 EX 0 1 64 0 1.00000 0.00000 LD 5 1 1 184 5.8001E7 LD 4 1 33 33 4 1600 LD 4 2 1 1 4 1750 LD 4 3 1 1 4 1750 LD 4 4 1 1 4 1750 LD 4 5 1 1 4 1750 LD 4 6 1 1 4 1750 LD 4 7 1 1 4 1750 LD 4 8 1 1 4 1750 LD 4 9 1 1 4 1750 LD 4 10 1 1 4 1750 LD 4 11 1 1 4 1750 FR 0 11 0 0 3.5 0.05 RP 0 181 1 1000 -90 0 1.00000 1.00000 EN Frank, Good morning. Let me start at the beginning. I have a loaded vertical on 75 meters. The combination of the antenna and ground measure about 40 Ohms at the antenna. The models all show such an antenna over a perfect ground should have a radiation resistance of between 3 and 4 Ohms. That says the antenna system is less the 10% efficient. This then is a journey to reduce ground resistance. Attempts to add radials and wire mesh to the ground have had very little if no effect. This leads to Reg's c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to a 2 meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms range. Together this should result is a 8 Ohm system. The ratio can be directly inferred as an performance improvement of 5 to 1 or 7 db. This is worth some effort. To answer your question the first step will be one coil and one radial. The objective is the get the antenna system close to 10 Ohms. From there I will experiment with adding radials and coils. I am not sure what to expect. Thanks - Dan Frank wrote: Not sure I understand what is going on Dan. Are you planning on loading each radial element? Frank "dansawyeror" wrote in message ... These results were from Reg's c_poise program. The band is 75 meters and the coils were about 70 uH. The coils were a relatively large diameter, on the order of a meter. The wire lengths were about 20 meters. By varying the length the coil, the coil wire may be varies from 1mm to 12mm. Richard Clark wrote: On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror wrote: The devil is in the details. Modeling shows large coils with 1 mm wire have a Q in the range of a few hundred. On the other hand a coil with 12 mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6 Ohms while the 12 mm coil is on the order of 1 Ohm. Given these model results it says there is a significant difference between 1 mm and 12 mm coils. Hi Dan, In the details, indeed. What is the LENGTH of wire in this 6 Ohm resistor? What is the LENGTH of wire in this 1 Ohm resistor? How many turns are in these "large coils?" What is their diameter? What is their solenoid length? Without these details, there is nothing said that is significant. 73's Richard Clark, KB7QHC |
| All times are GMT +1. The time now is 03:30 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com