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Please identify this vertical antenna
Hi,
I created a "omni-directional" vertical antenna that NEC-2 reports to have a free-space gain 4 dBi. The shape of the antenna looks like: ------+ A | | B | +-----+ C * (* = feed point) +-----+ | | | ------+ The lengths can be adjusted to give the antenna a 50 ohm feedpoint impedence. The overall length of wire forming the antenna (4A+2B+C) is on the order of 1.5\lambda and the height (2B) is something like \lambda. I built this antenna for 2-meters and it seems to perform quite well. The .nec files and parameters are available from my antenna pages at http://www.jedsoft.org/fun/antennas/omni.html. I am sure that I am not the first to create this simple antenna, nevertheless a google search has turned up nothing similar. Have you seen such an antenna before and if so, what is it called? I suspect that it belongs to some class of antennas (antennae?). I would like to give the proper credit and name for it on my web page. Also, if you can find a flaw in my NEC modeling of the antenna, please tell me. The prototype that I built does have an SWR of 1.05:1 as given by my uncalibrated meter at the design frequency. Thanks, --John |
Please identify this vertical antenna
|
Please identify this vertical antenna
John E. Davis wrote:
I created a "omni-directional" vertical antenna that NEC-2 reports to have a free-space gain 4 dBi. I created a somewhat similar antenna with 20+ dBi gain. http://www.qsl.net/w5dxp/SUPRGAIN.EZ -- 73, Cecil http://www.w5dxp.com |
Please identify this vertical antenna
"John E. Davis" wrote in message ... Hi, I created a "omni-directional" vertical antenna that NEC-2 reports to have a free-space gain 4 dBi. The shape of the antenna looks like: ------+ A | | B | +-----+ C * (* = feed point) +-----+ | | | ------+ The lengths can be adjusted to give the antenna a 50 ohm feedpoint impedence. The overall length of wire forming the antenna (4A+2B+C) is on the order of 1.5\lambda and the height (2B) is something like \lambda. I built this antenna for 2-meters and it seems to perform quite well. The .nec files and parameters are available from my antenna pages at http://www.jedsoft.org/fun/antennas/omni.html. I am sure that I am not the first to create this simple antenna, nevertheless a google search has turned up nothing similar. Have you seen such an antenna before and if so, what is it called? I suspect that it belongs to some class of antennas (antennae?). I would like to give the proper credit and name for it on my web page. Also, if you can find a flaw in my NEC modeling of the antenna, please tell me. The prototype that I built does have an SWR of 1.05:1 as given by my uncalibrated meter at the design frequency. Thanks, --John Hi John I really got interested in the configuration you show for the antenna. But, when I looked more closely to the Elevation Plane Pattern that looks so narrow (high gain), I realized that the antenna is very much the same pattern as a basic full wave center fed wire. The graduations on the plot graph was misleading to me. Perhaps there is something special about this antenna that I am missing. Jerry |
Please identify this vertical antenna
On Mon, 25 Sep 2006 11:19:25 -0700, Richard Clark
wrote: A Stub Fed Doublet. A Stub Fed Dipole. A Stub Fed Short Dipole. A Stub Fed Short Dipole with End Loading. Take your pick. I think I prefer "Stub Fed Doublet". Several comments. What's with the curious cogging of the SWR computed from NEC2? EZNEC predicts a quite smooth curve. Your measured values I was also wondering about that. The SWR values are computed by xnecview. It is conceivable that the choppiness of the curve is due to numerical stability issues, e.g., using the difference of 2 small numbers. Tonight I will dig out the xnecview source code and investigate further. suggest nearby losses. What do you do to snub common mode currents of the nearby transmission line that is precariously close, and co-linear with the polarization of your vertical dipole? For the prototype, I tried to run the coax perpendicular to the polarization to minimize the issue. Eventually I will use something like a 1-1 choke balun. In fact, at the bottom of the web page I suggest that something like that should be used. Of course I am open to other suggestions. Thanks, --John |
Please identify this vertical antenna
In article %4WRg.9158$Wi1.6469@trnddc06,
Jerry Martes wrote: Hi, I created a "omni-directional" vertical antenna that NEC-2 reports to have a free-space gain 4 dBi. The shape of the antenna looks like: ------+ A | | B | +-----+ C * (* = feed point) +-----+ | | | ------+ The lengths can be adjusted to give the antenna a 50 ohm feedpoint impedence. The overall length of wire forming the antenna (4A+2B+C) is on the order of 1.5\lambda and the height (2B) is something like \lambda. I built this antenna for 2-meters and it seems to perform quite well. The .nec files and parameters are available from my antenna pages at http://www.jedsoft.org/fun/antennas/omni.html. I am sure that I am not the first to create this simple antenna, nevertheless a google search has turned up nothing similar. Have you seen such an antenna before and if so, what is it called? I suspect that it belongs to some class of antennas (antennae?). I would like to give the proper credit and name for it on my web page. I really got interested in the configuration you show for the antenna. But, when I looked more closely to the Elevation Plane Pattern that looks so narrow (high gain), I realized that the antenna is very much the same pattern as a basic full wave center fed wire. The graduations on the plot graph was misleading to me. Perhaps there is something special about this antenna that I am missing. I believe that this antenna can probably be placed in the general class of center-fed collinears. Other antennas in this class include the center-fed fullwave, the classic Franklin antenna, and the EDZ (extended double Zepp). The "Super-J" is a somewhat-similar design, but is end-fed rather than center-fed. The center-fed collinears of this sort tend to have a high (and/or rather reactive) feedpoint impedance. They're usually fed through a section of transmission line - often shorted at the end and fed via a tap partway up the section... the "universal stub". Based on the dimensions you posted, it looks to me as if this antenna is pretty close to being an EDZ, but with the ends of the radiators bent back sideways. I'd guess that by bending the ends sideways, and fiddling with their lengths (and that of the matching section) you've been able to match the 50-ohm feedline impedance without needing a shorted/tapped matching section. The elevation pattern of the antenna shows a hint of the high-angle secondary lobes which characterize an EDZ. So, I'd conclude that you've developed a variant on the EDZ (or something partway between an EDZ and a center-fed fullwave) which yields slightly lower gain than an EDZ but has a simpler matching section. The one thing I'd watch out for, with this design, is the folded-back ends of the radiating arms. This design puts these high-voltage, high-impedance points right at the mast, and this might make this antenna more subject to mast/antenna coupling and de-tuning than a traditional EDZ or full-wave center-fed. The old ARRL VHF handbook has quite a bit of information on these sorts of collinears, and has a nice writeup on the "universal stub" matching technique (not very well known these days, but quite useful). -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Please identify this vertical antenna
John E. Davis wrote:
Hi, I created a "omni-directional" vertical antenna that NEC-2 reports to have a free-space gain 4 dBi. The shape of the antenna looks like: ------+ A | | B | +-----+ C * (* = feed point) +-----+ | | | ------+ The lengths can be adjusted to give the antenna a 50 ohm feedpoint impedence. The overall length of wire forming the antenna (4A+2B+C) is on the order of 1.5\lambda and the height (2B) is something like \lambda. I built this antenna for 2-meters and it seems to perform quite well. The .nec files and parameters are available from my antenna pages at http://www.jedsoft.org/fun/antennas/omni.html. I am sure that I am not the first to create this simple antenna, nevertheless a google search has turned up nothing similar. Have you seen such an antenna before and if so, what is it called? I suspect that it belongs to some class of antennas (antennae?). I would like to give the proper credit and name for it on my web page. Also, if you can find a flaw in my NEC modeling of the antenna, please tell me. The prototype that I built does have an SWR of 1.05:1 as given by my uncalibrated meter at the design frequency. Thanks, --John Congratulations John, you appear to have re-invented a version of the colinear vertical antenna on your own. I looked at your implimentation, and it seems to be quite well done. Keep it up, and have fun. tom K0TAR |
Please identify this vertical antenna
On Mon, 25 Sep 2006 11:19:25 -0700, Richard Clark
wrote: Several comments. What's with the curious cogging of the SWR computed from NEC2? EZNEC predicts a quite smooth curve. Your measured values I looked into this. The feedpoint impedence values Z(f) that NEC2 reports have discontinuities or discrete jumps, causing the predicted SWR to have the same. I imagine that this is a result of the numerical approximations and the segmentation used. Does EZNEC report the oscillations when the frequency increment is on the order of 0.01 MHz? What version of NEC does EZNEC use? I also tried using the extended thin wire kernel, but it did not help. Nor did increasing the segmentation. Thanks, --John |
Please identify this vertical antenna
On Mon, 25 Sep 2006 20:02:11 -0000, Dave Platt
wrote: The elevation pattern of the antenna shows a hint of the high-angle secondary lobes which characterize an EDZ. This is definitely noticable on a log plot. So, I'd conclude that you've developed a variant on the EDZ (or something partway between an EDZ and a center-fed fullwave) which yields slightly lower gain than an EDZ but has a simpler matching section. What sort of gain is expected from an EDZ? I tweaked the topology of my design a bit in the hope of getting a broader bandwidth, but instead got even more gain. For example, the version represented below has a minimum gain of more than 4.7 dBi (at the side) and more than 5.25 dBi in the forward direction. Previously I reported gain values that ran from 4.2-4.7 dBi. So this one represents a bit of an improvement. I may try building it this weekend. Thanks, --John CM Model: expt5 CM parms = [4.68255, 3.41606, 36.4806, 7.22131, 11.9807, 3.02775, ]; CM CM A1: 4-11/16 in. CM A2: 3-7/16 in. CM B1: 36-1/2 in. CM B2: 7-1/4 in. CM C: 12 in. CM D: 3 in. CM Wire diameter: 0.0640837 CM COM: (0 in., 9-1/16 in., 0 in.) CM BBOX: dX=0, dY=11.9807, dZ=90.4316 CM COM Turning radius: 9.06615 CM Min Turning radius: 5.99035 CE GW 1 3 0 0 9.10555 0 0 9.18245 0.000813863 GW 2 7 0 0 9.18245 0 0.30431 9.18245 0.000813863 GW 3 19 0 0.30431 9.18245 0 0.30431 10.1091 0.000813863 GW 4 5 0 0.30431 10.1091 0 0.30431 10.2925 0.000813863 GW 5 3 0 0.30431 10.2925 0 0.185373 10.2925 0.000813863 GW 6 3 0 0.30431 10.1091 0 0.217542 10.1091 0.000813863 GW 7 7 0 0 9.10555 0 0.30431 9.10555 0.000813863 GW 8 19 0 0.30431 9.10555 0 0.30431 8.17894 0.000813863 GW 9 5 0 0.30431 8.17894 0 0.30431 7.99552 0.000813863 GW 10 3 0 0.30431 7.99552 0 0.185373 7.99552 0.000813863 GW 11 3 0 0.30431 8.17894 0 0.217542 8.17894 0.000813863 GE 0 FR 0 201 0 0 144 0.02 EX 0 1 2 0 1 GN -1 0 0 0 0.0 0.0 0.0 0.0 0.0 0.0 RP 0 1 73 1001 90, 0, 1, 5 EN |
Please identify this vertical antenna
In article ,
John E. Davis wrote: The elevation pattern of the antenna shows a hint of the high-angle secondary lobes which characterize an EDZ. This is definitely noticable on a log plot. So, I'd conclude that you've developed a variant on the EDZ (or something partway between an EDZ and a center-fed fullwave) which yields slightly lower gain than an EDZ but has a simpler matching section. What sort of gain is expected from an EDZ? I tweaked the topology of my design a bit in the hope of getting a broader bandwidth, but instead got even more gain. For example, the version represented below has a minimum gain of more than 4.7 dBi (at the side) and more than 5.25 dBi in the forward direction. Previously I reported gain values that ran from 4.2-4.7 dBi. So this one represents a bit of an improvement. For an EDZ in isolation (no mast) I believe it's around 3 dBd or 5 dBi, plus or minus a hair. I modelled a copper-pipe EDZ, mounted at the top end of a conductive mast. This one came out with 5.85 dBi in the favored direction, and a 2.5 dB front-to-back ratio. CEDouble extended zepp for 2 meters GW 1 7 0 0 2 0 0 6.5 1.25 # Upper segment of mast GW 2 7 0 0 2 0 0 -2 1.25 # Middle segment of mast GW 3 100 0 0 -2 0 0 -112.5 1.25 # Lower segment of mast GW 4 15 0 0 2 13 0 2 0.5 # Upper support bar GW 5 15 0 0 -2 13 0 -2 0.5 # Lower support bar GW 6 7 13 0 2 13 0 -2 0.5 # Shorting bar GW 7 7 13 0 2 17 0 2 0.5 # To top of balun GW 8 7 13 0 -2 17 0 -2 0.5 # To bottom of balun GW 9 15 17 0 2 28 0 2 0.5 # To top arm GW 10 15 17 0 -2 28 0 -2 0.5 # To bottom arm GW 11 40 28 0 2 28 0 46 0.5 # Upper arm GW 12 40 28 0 -46 28 0 -2 0.5 # Lower arm GW 13 5 17 0 2 17 0 -2 0.5 # Feedline attachment GS 0 0 0.0254 GE 0 EX 0 13 3 0 1.0 FR 0 1 0 0 145.27 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 RP 0 61 72 1101 0.0 0.0 3 5 XQ EN A stacked pair of them on a single mast yields 8.85 dBi in the favored direction, with 2.38 dB front-to-back ratio. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Please identify this vertical antenna
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Please identify this vertical antenna
On Tue, 26 Sep 2006 22:36:53 -0700, Richard Clark
wrote: I've been using various flavors of E(L/Z)NEC for more than a decade and I've never seen such dramatic cogging of the data that was not attributable to construction (notably fractals). Your data is stranger yet in having correlated noise on the left, and uncorrelated noise on the right. Please look at the ftp://space.mit.edu/pub/davis/misc/nec/swr.png for a plot of the SWR using a spacing of 0.01 MHz. I suspect that the noise that is showing up may be due to truncation error. I believe that spacings of higher values, e.g., 0.2 MHz result in a different sampling of the noise. The version I am using (see http://packages.debian.org/stable/hamradio/nec) contains this warning: This version contains code which hasn't been extensively tested for errors, which was input by hand from a report -- use with care. The numerics are currently only SINGLE PRECISION. If EZNEC were available for linux, I would look into it. Also, can it be driven in "batch" mode without a GUI? Thanks, --John |
Please identify this vertical antenna
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Please identify this vertical antenna
Richard Clark wrote:
On 27 Sep 2006 06:52:46 GMT, (John E. Davis) wrote: . . . If EZNEC were available for linux, I would look into it. Also, can it be driven in "batch" mode without a GUI? There have been various reports of success and failure when Windows emulators have been used. I cannot report any personal experience because my Linux machine is largely confined to Server development (XAMMP/Wiki/MySQL/RubyOnRails). The last reports I've gotten are that Wine, the Linux Windows emulator, isn't able to open the EZNEC manual, and has at least one other problem with EZNEC. I've gotten several reports that the SoftWindows emulator for the Mac runs even the professional versions of EZNEC flawlessly. There isn't, and won't be in the foreseeable future, a native Linux or Mac version of EZNEC; the market is simply too small. EZNEC can be run in something resembling batch mode with MultiNec (http://www.ac6la.com/). The NEC-2 calculating engine in the demo and standard EZNEC program types contains a mixture of single and double precision variables which does considerably better than a fully single precision implementation but with only a slightly greater memory requirement. EZNEC+ and the professional programs also include a fully double-precision implementation. None of these are identical to NEC-2 (of which there are several slightly different versions in circulation); EZNEC has consolidated scattered constant values, added protections against numeric overflow, incorporates third-party math libraries for some calculations, and has a few obscure bugs in the code fixed, among other differences. Although EZNEC doesn't implement all the features of NEC-2 (patches, for example), it has features which NEC-2 doesn't, such as a comprehensive geometry check and provision for wire insulation (and of course the GUI). I've also found some optimizations done by various compilers which cause errors or crashes in some cases, and of course these are avoided when compiling EZNEC's calculating engines. In fact, I'm just now working with a compiler manufacturer in tracking down what looks like a bug I found in a new compiler I'm considering using for future versions. NEC-2 is free, and people pay for EZNEC. They do get something for it. Roy Lewallen, W7EL |
Please identify this vertical antenna
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Please identify this vertical antenna
On Wed, 27 Sep 2006 04:40:51 -0000, Dave Platt
wrote: I modelled a copper-pipe EDZ, mounted at the top end of a conductive mast. This one came out with 5.85 dBi in the favored direction, and a 2.5 dB front-to-back ratio. Have you considered using the much simpler moxon? This one has a forward gain of 5.6-6.4dBi (6.2@146MHz) and a front-to-back ratio of 18-31dBi (29@146MHz). It uses #12 AWG wire. Thanks, --John CM Model: moxon for 2m CM parms = [29.1337, 4.18345, 1.4995, 5.70003, ]; CM CM A: 29-1/8 in. CM B: 4-3/16 in. CM C: 1-1/2 in. CM D: 5-11/16 in. CM Wire Diameter: 0.0808081 CE GW 1 3 -0.10626 0 8.774 0 0 8.774 0.00102626 GW 2 15 0 0 8.774 0 0 9.514 0.00102626 GW 3 3 0 0 9.514 -0.10626 0 9.514 0.00102626 GW 4 3 -0.144347 0 9.514 -0.289128 0 9.514 0.00102626 GW 5 15 -0.289128 0 9.514 -0.289128 0 8.774 0.00102626 GW 6 3 -0.289128 0 8.774 -0.144347 0 8.774 0.00102626 GE 0 FR 0 401 0 0 144 0.01 EX 0 2 8 0 1 GN -1 0 0 0 0.0 0.0 0.0 0.0 0.0 0.0 RP 0 1 73 1001 90 0 1 5 EN |
Please identify this vertical antenna
On Wed, 27 Sep 2006 00:19:53 -0700, Richard Clark
wrote: Yow! That is a lot of trash. For most uses, it is not so bad. For example, elsewhere in this thread I posted the .nec file for a 2m-moxon. The corresponding plot of the SWR may be seen at ftp://space.mit.edu/pub/davis/misc/nec/moxon_swr.png. The noise is still there, but the amplitude is much smaller and would not be noticable on a coarser frequency grid. Thanks, --John |
Please identify this vertical antenna
In article ,
Walter Maxwell wrote: For an EDZ in isolation (no mast) I believe it's around 3 dBd or 5 dBi, plus or minus a hair. I modelled a copper-pipe EDZ, mounted at the top end of a conductive mast. This one came out with 5.85 dBi in the favored direction, and a 2.5 dB front-to-back ratio. Have I missed something here? As I understand the EDZ (is it not the Extended Double Zepp?) it comprises a center-fed doublet with a 5/8 wl wire on each side of the feed point. It's broadside gain is about 3.1 dBd, with a narrower lobe than that of a dipole, from which the gain over a dipole is obtained. Am I correct so far? Yup. If so, then we have only a single radiator. How then can there be a front-to-back ratio? The model I developed/posted was for an EDZ, which is side-mounted at the top of a conductive mast. One half of the doublet sticks up above the mast "in the clear", but the other half runs down parallel to the mast, perhaps a foot away. As with any side- or tower-mounted antenna, there's some amount of reflection from the mast, and this is enough to create a few dB of "front to back" ratio. If the antenna were modelled (or used) in isolation, with no mast and with the feedline running out sideways, the "front to back" ratio would be unity or very close to it. Just delete the mast pipe from the model I posted and re-run NEC. The design/installation data for Telewave's side-mounted folded-dipole arrays show several different patterns, ranging from something very close to a cardioid, to an "off-center circular" pattern, to a nearly perfect circular pattern. All of these patterns can be achieved using the same antenna array, by simply altering the length of the side-mount arms which support the dipoles beside the mast or tower. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Please identify this vertical antenna
In article ,
John E. Davis wrote: I modelled a copper-pipe EDZ, mounted at the top end of a conductive mast. This one came out with 5.85 dBi in the favored direction, and a 2.5 dB front-to-back ratio. Have you considered using the much simpler moxon? This one has a forward gain of 5.6-6.4dBi (6.2@146MHz) and a front-to-back ratio of 18-31dBi (29@146MHz). It uses #12 AWG wire. Thanks, --John If I were actually seeking a high front-to-back ratio, a Moxon would be a good choice! I actually developed the EDZ models for a different application... the main antenna on a 2-meter repeater installation. We want a reasonable amount of gain, and a near-omnidirectional pattern. The high front-to-back ratio of a Moxon would not be appropriate in this case... the 2.5 dB ratio of the side-mounted EDZ is probably as much as we'd want to accept, given the shape and size of our service area. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Please identify this vertical antenna
Richard Clark wrote:
Hi John, Yes, this confirms the shift to double precision in EZNEC lowering artifacts in the fine data. However, I think it goes beyond simple matters of single or dual precision math. When I was designing Fourier Analysis packages while I was on contract to HP, I discovered there was a world of variability in math library's transcendental functions. Microsoft's product was abysmal, whereas Borland's was superlative. A telling example is that for the transform of a sine wave into the frequency domain under Microsoft math libraries, the noise floor was at 60 to 80 dB below the fundamental peak with harmonics. When I switched to Borland math libraries, there was a single bin response and the noise floor plunged to 200dB down! snip 73's Richard Clark, KB7QHC Richard I am not surprised with your result after having used various MS compilers over the years. Do you have any idea what the real differences were in the libraries? Borland C always seemed better, more robust at error handling, and more accurate. I noticed similar problems back in the late 80's with MS C, but never really needed the precision, and work pressure being what it was.... tom K0TAR |
Please identify this vertical antenna
On Wed, 27 Sep 2006 19:47:06 -0500, Tom Ring
wrote: Do you have any idea what the real differences were in the libraries? Hi Tom, I can only speculate from my experience coding various expansion series before the 8087 was generally available. My guess is they went with the first one in a cookbook - Newton's method comes to mind, but that is of vague recollection. It is generally useful as a first pass method. M$ became extinct in the Pascal marketplace soon after. I also moved on into C++ in the late 80s (a local company here wrote one of the first cross-compilers). The M$ crowd thought they would take that one on too. In 1990 they asked me to come in and give classes. What a fiasco. The first question was how to do inline code. They were arrogant to the point of wanting to call "their" version C++++ with the +s stacked in pairs to produce #. Can anyone guess how long C-sharp took to get to market? 73's Richard Clark, KB7QHC |
New version of my 2m omni (was Please identify this vertical antenna)
On 27 Sep 2006 02:49:55 GMT, I wrote wrote:
What sort of gain is expected from an EDZ? I tweaked the topology of my design a bit in the hope of getting a broader bandwidth, but instead got even more gain. For example, the version represented below has a minimum gain of more than 4.7 dBi (at the side) and more than 5.25 dBi in the forward direction. Previously I reported gain values that ran from 4.2-4.7 dBi. So this one represents a bit of an improvement. I may try building it this weekend. Thanks, --John I found time this weekend to construct this antenna and it seems to work quite well. See http://www.jedsoft.org/fun/antennas/omni.html for the details including a picture of the antenna. While testing it, I made a contact through a distant repeater (40 miles away) and was told that the signal was solid. This was with the antenna in its test position with the center about 10 feet off the ground and the transmitter power at 5 watts. Unfortunately I cannot be more quantitation than that. Unless I have overlooked some other design, this seems to be an extremely simple and effective home-brew antenna. Comments welcome. Thanks, --John |
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