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Two Element Beams
You must have missed the announcement I posted not long ago. The article
about transmission line phasing systems ("The Simplest Phased Array Feed System - That Works") is now available at http://eznec.com/Amateur/Articles/. And there's also a new Windows Simpfeed program which takes EZNEC (or other modeling program) reported feedpoint impedances as its input (no mutual Z calculation necessary) and calculates the feedline lengths necessary for proper phasing. Click the Simpfeed link at that same URL to get it. It's considerably more versatile than the older DOS programs. A short manual, including a detailed example (using both the EZNEC demo and the standard EZNEC program type), can be viewed by clicking the Help button in the program window. EZNEC example files CardTL.EZ and 4SqTL.EZ illustrate the results of using this feed method. The new program does all calculations in double precision, so you'll find the values it generates are slightly different than the values in the example files -- they're actually better. Roy Lewallen, W7EL Cecil Moore wrote: Years ago I experimented with two-element beams where both elements were driven. Roy, W7EL, has some BASIC programs on his web page that allows the calculation of phasing harnesses for such antennas. The disadvantage is that one must know the mutual coupling impedance between the two elements. . . . |
Roy Lewallen wrote:
And there's also a new Windows Simpfeed program which takes EZNEC (or other modeling program) reported feedpoint impedances as its input (no mutual Z calculation necessary) and calculates the feedline lengths necessary for proper phasing. Click the Simpfeed link at that same URL to get it. It's considerably more versatile than the older DOS programs. What is the URL for the Windows Simpfeed program link? I don't see it on your web page. (Do you remember I sent you a DOS BASIC program about a decade ago that does that calculation without needing Rm and Xm?) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Roy Lewallen wrote:
Simpfeed program which takes EZNEC (or other modeling program) reported feedpoint impedances as its input (no mutual Z calculation necessary) and calculates the feedline lengths necessary for proper phasing. Click the Simpfeed link at that same URL to get it. Sorry, I wasn't reading closely enough and was looking for it on your web page. I found it. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
i am not clear on how this antenna would look, when i think of 2 elements "" phased or simul driven i presumed it would sorta look like a typical beam elements in parrallel spaced apart that being the case , i am not clear on how changing the feedpoint alters the ew ns direction unless of course the antenna is like a cross the gain seemed nice wouldn't mind trying one, my catch is i am using a sgc tuner to feed my present dipole, i suppose i could just take it's output and feed both 'elements' be a neet experiment thanks m Years ago I experimented with two-element beams where both elements were driven. Roy, W7EL, has some BASIC programs on his web page that allows the calculation of phasing harnesses for such antennas. The disadvantage is that one must know the mutual coupling impedance between the two elements. In article , Cecil Moore wrote: Given that EZNEC will output the feedpoint impedances for both elements, for a common class of two-element beams, the mutual coupling impedance can be calculated from the EZNEC data. Assuming the two-element beam consists of two identical center-fed elements and assuming that the feedpoint current magnitudes are equal, one can design the beam to meet certain specifications, obtain the feedpoint impedances from EZNEC, and calculate the mutual coupling to be entered into Roy's BASIC phasing software. Lewell1.bas program available as simpfeed.zip on www.eznec.com. One advantage of a wire beam like this is that the direction of maximum gain can be reversed by changing the feedpoint position on the coaxial phasing harness. Good E-W or N-S beam performance is obtained with one fixed wire beam on the lower bands. -- 73, Cecil, W5DXP |
Cecil Moore, W5DXP wrote:
"Years ago I experimented with two-element beams where both elements were driven." J.D. Kraus, inventor of the W8JK beam obviously did too. He found the most gain he could get is the configuration of the W8JK. Some of his results are summarized in Table 6-2 on page 192 of the 3rd edition of "Antennas".Cecil has this book, I believe. Kraus reports the W8JK gain as 6.1 dBi. The W8JK has two dipoles spaced at 1/8 wavelength and fed 180-degrees out of phase. Close coupling causes super gain but a very low drivepoint resistance. Kraus calculates the drivepoint impedance as 9+j48 ohms on page 186. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
Cecil Moore, W5DXP wrote: "Years ago I experimented with two-element beams where both elements were driven." J.D. Kraus, inventor of the W8JK beam obviously did too. He found the most gain he could get is the configuration of the W8JK. . . The W8JK doesn't provide the most gain of any two element array of half wavelength elements for a given spacing. At 0.1 wavelength spacing, a two element array fed with a 166 degree relative phase angle provides about 1.4 dB greater gain than a W8JK. At 0.25 wavelength spacing, 142 degree phasing gives the highest gain, just over 1 dB greater than a W8JK. These phasings also provide a higher feedpoint impedance than the W8JK, which results in decreased conductor loss and easier matching. The W8JK has some advantages over other two element arrays, but having the highest gain isn't one of them. Roy Lewallen, W7EL |
Roy, W7EL wrote:
"The W8JK doesn`t provide thye most gain of any two element array of half wavelength elements for a given spacing." The W8JK had the highest gain of the 5 examples compared in the table. The advantage of EZNEC is shown in Roy`s posting. Roy also wrote: "At 0.25 wavelength spacing, 142 degree phasing gives the highest gain, just over 1 dB greater than a W8JK. These phasings also provide a higher nfeedpoint impedance than a W8JK,---." I`d rather have Roy`s antenna. Best regards, Richard Harrison, KB5WZI |
ml wrote:
that being the case , i am not clear on how changing the feedpoint alters the ew ns direction Referring to the files I attached yesterday: If the current in element#2 lags the current in element#1 then you get 12 dBi gain in one direction. If the current in element#2 leads the current in element#1 then you get 12 dBi gain in the opposite direction. The phasing feedline might look something like this with coaxial 'T' connectors installed at points "x" and 'y': Element#1--------x----------y--------Element#2 Assuming connecting the RF at point 'x' will yield 12 dBi gain in a Westward direction, connecting the RF at point 'y' will yield 12 dBi gain in an Eastward direction without moving the elements. -- 73, Cecil, W5DXP ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
The method is described briefly in the article posted on my web site.
If someone gives you the self and mutual impedances of two elements and the lengths of two feedlines connecting them to a common point, it's a fairly simple matter to calculate the resulting element currents. What the program does is work the same problem backward. That is, given the self and mutual impedances of the elements (or in the case of the new program, the feedpoint impedances when properly fed), it finds the feedline lengths which will produce the desired current ratio *in those two impedances*. Years ago I got interested in the problem and figured out how to work it in that direction. It involves a bunch of variable transformations to keep the equation sizes reasonable, and results in a nice, closed-form solution. Some time after I came up with the method, I spotted an article in Ham Radio magazine which described a solution using an iterative approach -- it solved the problem in the easy direction, looked at the result, modified the feedline lengths, tried again, and so forth. That works (I had done it that way before figuring out the closed form solution), but can be time consuming -- at least it could with the computers of the time --, and you have to be careful with the algorithm to keep the process stable. I wrote to the author of the Ham Radio article telling him of my method, and he suggested that I write it up. I had just gone through a lengthy period of very unpleasant dealings with magazines and editors (particularly Rich Rosen at Ham Radio), and had no interest in having more of it. So he ended up writing the paper describing the method in step-by-step fashion. You can find it in "A Voltage-Matching Method for Feeding Two-Tower Arrays" by A. Christman, in IEEE Trans. on Broadcasting, June 1987. Or if you're a masochist, you can try untangling the GWBASIC spaghetti code in the original DOS programs. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: These phasings also provide a higher feedpoint impedance than the W8JK, which results in decreased conductor loss and easier matching. Where your simpfeed method really makes sense is with beams where the elements are more than 1/2WL long. For instance, attached is the 33 ft. long, two-driven-elements spaced at ten feet used on 17m. The impedances are high enough to use 300 ohm twinlead for the phasing and the feedpoint impedance at the phasing harness is around 25 ohms. Roy, what is the secret to balancing those currents in the two elements? With the same Z0 phasing lines, the SWR circles don't intersect so the impedances looking into those phasing lines is never equal. Does my question make sense? -- 73, Cecil, W5DXP |
There are a couple of distinct advantages of the W8JK over the antennas
I described. One is that it can be fed with two equal lengths of transmission line to the elements, one being given a physical half twist to effect the phase reversal. Then you have an antenna whose properties remain the same over an extremely wide bandwidth. The second is that the free-space pattern consists of two relatively narrow lobes in the vertical plane, with an overhead null. This results in a concentration of radiation at lower angles than you'll get with a typical Yagi or most other two element horizontal antennas. The tradeoffs are that because of the bidirectional pattern, half the radiation doesn't do you any good; there's no front-back ratio (although it's also poor on the maximum-gain antennas I described); and loss has to be managed and can potentially be a problem because of the low feedpoint impedances. There's no single perfect antenna -- you pays your money and you makes your choice. As Richard Heinlein so succinctly said, TANSTAAFL. Roy Lewallen, W7EL Richard Harrison wrote: Roy, W7EL wrote: "The W8JK doesn`t provide thye most gain of any two element array of half wavelength elements for a given spacing." The W8JK had the highest gain of the 5 examples compared in the table. The advantage of EZNEC is shown in Roy`s posting. Roy also wrote: "At 0.25 wavelength spacing, 142 degree phasing gives the highest gain, just over 1 dB greater than a W8JK. These phasings also provide a higher nfeedpoint impedance than a W8JK,---." I`d rather have Roy`s antenna. Best regards, Richard Harrison, KB5WZI |
I've seen a setup of 3 phased verticals (in a 60degree triangle space)
where - with the help of switches, relays, and various lengths of coax, the operator could choose any of 6 directions with a switch, then the relays would cut in appropriate phasing lengths . The wiring of the relays would keep me busy for quite a while. Heck - grandma used to keep us occupied by putting molasses on our hand and giving us a feather |
Roy Lewallen wrote:
There's no single perfect antenna -- you pays your money and you makes your choice. As Richard Heinlein so succinctly said, TANSTAAFL. Roy Lewallen, W7EL Robert Anson Heinlein. A master in his field, as you are in yours. tom K0TAR |
My apology, to the readers and to the late *Robert* Heinlein.
Roy Lewallen, W7EL Tom Ring wrote: Roy Lewallen wrote: There's no single perfect antenna -- you pays your money and you makes your choice. As Richard Heinlein so succinctly said, TANSTAAFL. Roy Lewallen, W7EL Robert Anson Heinlein. A master in his field, as you are in yours. tom K0TAR |
On Tue, 19 Apr 2005 19:17:34 -0700, Roy Lewallen
wrote: My apology, to the readers and to the late *Robert* Heinlein. No problem; I'm sure he won't mind. |
What would happen if you isolated that second driven element from the boom
(the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? Regards, John "Roy Lewallen" wrote in message ... There are a couple of distinct advantages of the W8JK over the antennas I described. One is that it can be fed with two equal lengths of transmission line to the elements, one being given a physical half twist to effect the phase reversal. Then you have an antenna whose properties remain the same over an extremely wide bandwidth. The second is that the free-space pattern consists of two relatively narrow lobes in the vertical plane, with an overhead null. This results in a concentration of radiation at lower angles than you'll get with a typical Yagi or most other two element horizontal antennas. The tradeoffs are that because of the bidirectional pattern, half the radiation doesn't do you any good; there's no front-back ratio (although it's also poor on the maximum-gain antennas I described); and loss has to be managed and can potentially be a problem because of the low feedpoint impedances. There's no single perfect antenna -- you pays your money and you makes your choice. As Richard Heinlein so succinctly said, TANSTAAFL. Roy Lewallen, W7EL Richard Harrison wrote: Roy, W7EL wrote: "The W8JK doesn`t provide thye most gain of any two element array of half wavelength elements for a given spacing." The W8JK had the highest gain of the 5 examples compared in the table. The advantage of EZNEC is shown in Roy`s posting. Roy also wrote: "At 0.25 wavelength spacing, 142 degree phasing gives the highest gain, just over 1 dB greater than a W8JK. These phasings also provide a higher nfeedpoint impedance than a W8JK,---." I`d rather have Roy`s antenna. Best regards, Richard Harrison, KB5WZI |
Hal Rosser wrote:
I've seen a setup of 3 phased verticals (in a 60degree triangle space) where - with the help of switches, relays, and various lengths of coax, the operator could choose any of 6 directions with a switch, then the relays would cut in appropriate phasing lengths . G3HCT (now VK4OQ) used this system for 40m. By phasing any pair you have a choice of six 2-element beams, with the third element inactive (open-circuit). The gain is about 1.5dB lower than a four-square, comparing both beams in their best (forward) direction, but the triangle has more directions to choose from, so in some directions it's actually ahead of the 4sq. The verticals were quite closely-spaced, and phased to give *two* rearward nulls at around +/-120deg. That gave a total of 12 switchable nulls on receive, which can be very important in European QRM. The wiring of the relays would keep me busy for quite a while. Four DPDT relays take care of everything. Heck - grandma used to keep us occupied by putting molasses on our hand and giving us a feather 'Eck - i' Yorkshire we only had... [insert rest of Python sketch here]. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
John Smith wrote:
What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? That's just the sort of thing antenna modeling programs are for. And they're good at it. Roy Lewallen, W7EL |
LOL!!! Hmm, I wonder if anyone sells one? grin
Warmest regards, John "Roy Lewallen" wrote in message ... John Smith wrote: What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? That's just the sort of thing antenna modeling programs are for. And they're good at it. Roy Lewallen, W7EL |
John Smith wrote:
What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? You can get all the FB you want using two driven elements and Roy's simpfeed software. -- 73, Cecil, W5DXP ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
I am going out today and see if I can't fit this all on a boom six foot long
or less, drop that 1/4 wave phase reversal line, replace it with a 1:1 phase reversal balun and see just how close I can jam two phase reversed driven elements together... I need a tan anyway... grin Regards, John "Cecil Moore" wrote in message ... John Smith wrote: What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? You can get all the FB you want using two driven elements and Roy's simpfeed software. -- 73, Cecil, W5DXP ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
28.4 Mhz of course!
John "John Smith" wrote in message ... I am going out today and see if I can't fit this all on a boom six foot long or less, drop that 1/4 wave phase reversal line, replace it with a 1:1 phase reversal balun and see just how close I can jam two phase reversed driven elements together... I need a tan anyway... grin Regards, John "Cecil Moore" wrote in message ... John Smith wrote: What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? You can get all the FB you want using two driven elements and Roy's simpfeed software. -- 73, Cecil, W5DXP ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Mon, 18 Apr 2005 14:05:02 -0700, Roy Lewallen
wrote: You must have missed the announcement I posted not long ago. The article about transmission line phasing systems ("The Simplest Phased Array Feed System - That Works") is now available at http://eznec.com/Amateur/Articles/. And there's also a new Windows Simpfeed program which takes EZNEC (or other modeling program) reported feedpoint impedances as its input (no mutual Z calculation necessary) and calculates the feedline lengths necessary for proper phasing. Click the Simpfeed link at that same URL to get it. It's considerably more versatile than the older DOS programs. A short manual, including a detailed example (using both the EZNEC demo and the standard EZNEC program type), can be viewed by clicking the Help button in the program window. EZNEC example files CardTL.EZ and 4SqTL.EZ illustrate the results of using this feed method. The new program does all calculations in double precision, so you'll find the values it generates are slightly different than the values in the example files -- they're actually better. Nice job! |
Indeed I do sell modeling programs. But it's not necessary to buy one to
answer your question. The EZNEC demo or any of several other free programs including NEC-2 is adequate. Roy Lewallen, W7EL John Smith wrote: LOL!!! Hmm, I wonder if anyone sells one? grin Warmest regards, John "Roy Lewallen" wrote in message ... John Smith wrote: What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? That's just the sort of thing antenna modeling programs are for. And they're good at it. Roy Lewallen, W7EL |
Roy, I am just joking with ya! Don't let the "angry tone" of some mislead
ya.... Warmest regards, John "Roy Lewallen" wrote in message ... Indeed I do sell modeling programs. But it's not necessary to buy one to answer your question. The EZNEC demo or any of several other free programs including NEC-2 is adequate. Roy Lewallen, W7EL John Smith wrote: LOL!!! Hmm, I wonder if anyone sells one? grin Warmest regards, John "Roy Lewallen" wrote in message ... John Smith wrote: What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? That's just the sort of thing antenna modeling programs are for. And they're good at it. Roy Lewallen, W7EL |
I spend much time designing, flow charting, pseudo-coding, and running
compilers and linkers... I am a "hard head" here... wanna get my hands dirty... as Reg said, "... get some wire in the air..." Regards, John "Roy Lewallen" wrote in message ... Indeed I do sell modeling programs. But it's not necessary to buy one to answer your question. The EZNEC demo or any of several other free programs including NEC-2 is adequate. Roy Lewallen, W7EL John Smith wrote: LOL!!! Hmm, I wonder if anyone sells one? grin Warmest regards, John "Roy Lewallen" wrote in message ... John Smith wrote: What would happen if you isolated that second driven element from the boom (the one you are effecting the phase-shift in, and added another reflector ( naturally it is in proper phase) behind it? Could you get the best of two worlds? The advantage of the phase-shift plus a FB ratio? That's just the sort of thing antenna modeling programs are for. And they're good at it. Roy Lewallen, W7EL |
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