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loops and 4:1 baluns
I have started to experiment with EZNEC and am
modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD |
loops and 4:1 baluns
On Jan 16, 6:52*pm, Tad Danley wrote:
I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. *I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. *I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD It's harder to build a 2:1 balun.. a 4:1 is a 2:1 turns ratio, and more common (yes, one can do 3:2, that's 1.5:1 turns, 2:25:1 Z) |
loops and 4:1 baluns
7:5 turns ratio is 2:1 balun;
3:2 turns, as suggested, is 2.25:1: SWR 1.1:1 is good... Gianluca |
loops and 4:1 baluns
"Tad Danley" wrote in message ... I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD the simpler match is 1/4 wave of 75 ohm cable. |
loops and 4:1 baluns
the simpler match is 1/4 wave of 75 ohm cable.
For a narrow band... Gianluca |
loops and 4:1 baluns
"Tad Danley" wrote in message ... I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD -------- I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. This is not a surprise, really. Few things in electronics are exact as we humans like to assume, as you well know. Good seeing your post, OM. Ed Cregger, N2ECW former NM2K |
loops and 4:1 baluns
"Ed Cregger" wrote in message ... "Tad Danley" wrote in message ... I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD -------- I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. This is not a surprise, really. Few things in electronics are exact as we humans like to assume, as you well know. the baluns are exact, the practical antennas aren't. |
loops and 4:1 baluns
Tad Danley wrote:
I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? The resonant feedpoint of the 80m loop that I modeled with EZNEC is 115 ohms. Without a 4:1 at the feedpoint, the 50 ohm SWR is 2.3:1 inviting foldback. With a 4:1 balun, the 50 ohm SWR is 1.7:1 with no foldback. It is rare for the feedpoint resistance of a loop to be exactly 100 ohms. Of course, if the loop is fed with high-Z0 ladder-line, the 100 ohm feedpoint resistance is transformed to a higher impedance value where a 4:1 balun might be more effective. For single-band operation, most hams simply feed the loop with 1/4WL of Z0=75 ohm coax (quarter-wave transformer). -- 73, Cecil http://www.w5dxp.com |
loops and 4:1 baluns
"Dave" wrote in message ... "Ed Cregger" wrote in message ... "Tad Danley" wrote in message ... I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD -------- I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. This is not a surprise, really. Few things in electronics are exact as we humans like to assume, as you well know. the baluns are exact, the practical antennas aren't. Only in theory. Such things as variances in construction materials from one batch to another and the variations that one human will introduce to construction versus another human also induce characteristics that do not always jibe with theory. I admit that I am argueing a very fine point here, Dave, but folks without any electronics education, but who have pursued electronics theory as part of their amateur radio advocation, are sometimes prone to thinking that everything is exact. In the real physical world, few things are exact. Ask any technician or machinist. Ed, N2ECW |
loops and 4:1 baluns
On Sat, 17 Jan 2009 12:48:05 -0500, "Ed Cregger"
wrote: I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. the baluns are exact, the practical antennas aren't. Only in theory. Such things as variances in construction materials from one batch to another and the variations that one human will introduce to construction versus another human also induce characteristics that do not always jibe with theory. I admit that I am argueing a very fine point here, Dave, but folks without any electronics education, but who have pursued electronics theory as part of their amateur radio advocation, are sometimes prone to thinking that everything is exact. In the real physical world, few things are exact. Ask any technician or machinist. Any technician or machinist has only a remote association with exact anyway. I've calibrated their tools and know how inexact they are. However, returning to the context of BalUns, a person can choose to fail, or simply fumble along when it comes to their design, construction, or application - but this is not a performance fault of the class of BalUn. Using your 160M BalUn for 1.2GHz work isn't a blight on the BalUn, but on the user's inappropriate application (hammering in a screw for example). The test data I've seen for careful constructions have remarkable attributes that defy typical construction projects pursuing other goals. Jerry Sevick's work reveals less than 0.02dB variation of insertion loss over the HF range for one of his constructions. The value of insertion loss it does present is less than 0.1dB. The ability to duplicate his work is not outside the capability of any individual who writes to this group - but anyone could certainly slop it into oblivion if care was not high in their mind. The specs I offered above came of simply opening the book and describing the first page that offered test results. Scanning further for better examples yields better examples. As a class, BalUns are rather exceptional performers. So, to this casual off-hand remark of BalUns not being as "exact" in practice as in theory begs the question: "How exact?" When I see such manufactured controversies conjoined (through other authors) with turns-ratio, the discussion of BalUn operation is showing stress fractures in understanding - not theory. 73's Richard Clark, KB7QHC |
loops and 4:1 baluns
Ed Cregger wrote:
I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. This is not a surprise, really. Few things in electronics are exact as we humans like to assume, as you well know. Good seeing your post, OM. Ed Cregger, N2ECW former NM2K The whole problem is "liking to assume" that things are simpler than they are. When the theory you apply is too simple, guess what -- you'll find that the real thing doesn't behave as your oversimplified "theory" predicts. Theory works just fine, and accurately predicts how a real object will work. Oversimplified "theory" often doesn't work so well. A well made balun or RF transformer behaves reasonably well like an ideal transformer, that is, infinite winding inductance, no coupling capacitance, zero leakage inductance, no loss, and so forth, but only under quite a narrow range of circumstances. Those circumstances include being terminated with a fairly narrow range of impedances and over a limited frequency range. Usually, one side is designed to be terminated with 50 ohms, purely resistive. That means the other side of a 4:1 balun has to be terminated with something fairly close to 200 or 12.5 ohms (depending on how it's designed), also resistive, in order for it to work as intended. If the impedance differs very much at all from that value, you'll find that the transformation ratio is no longer 4:1, and that the balun will add a series and/or shunt impedance to the circuit. This can be accounted for by theory, but only with great difficulty since it requires careful characterization of the core and windings. People tend to design, and often test, a 4:1 balun in a 50 ohm environment, then attach it to a multiband antenna that has rather extreme (but entirely predictable) impedance variations. Then they're surprised because the impedance seen looking into the balun isn't 4 times or 1/4 times the antenna impedance, but is something wildly different. They shouldn't be. A 4:1 balun or transformer that effects a nice 4:1 impedance transformation when presented with a very wide range of termination impedances simply doesn't exist. Any "theory" that predicts it is oversimplified and invalid. Roy Lewallen, W7EL |
loops and 4:1 baluns
"Roy Lewallen" wrote in message treetonline... Ed Cregger wrote: I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. This is not a surprise, really. Few things in electronics are exact as we humans like to assume, as you well know. Good seeing your post, OM. Ed Cregger, N2ECW former NM2K The whole problem is "liking to assume" that things are simpler than they are. When the theory you apply is too simple, guess what -- you'll find that the real thing doesn't behave as your oversimplified "theory" predicts. Theory works just fine, and accurately predicts how a real object will work. Oversimplified "theory" often doesn't work so well. A well made balun or RF transformer behaves reasonably well like an ideal transformer, that is, infinite winding inductance, no coupling capacitance, zero leakage inductance, no loss, and so forth, but only under quite a narrow range of circumstances. Those circumstances include being terminated with a fairly narrow range of impedances and over a limited frequency range. Usually, one side is designed to be terminated with 50 ohms, purely resistive. That means the other side of a 4:1 balun has to be terminated with something fairly close to 200 or 12.5 ohms (depending on how it's designed), also resistive, in order for it to work as intended. If the impedance differs very much at all from that value, you'll find that the transformation ratio is no longer 4:1, and that the balun will add a series and/or shunt impedance to the circuit. This can be accounted for by theory, but only with great difficulty since it requires careful characterization of the core and windings. People tend to design, and often test, a 4:1 balun in a 50 ohm environment, then attach it to a multiband antenna that has rather extreme (but entirely predictable) impedance variations. Then they're surprised because the impedance seen looking into the balun isn't 4 times or 1/4 times the antenna impedance, but is something wildly different. They shouldn't be. A 4:1 balun or transformer that effects a nice 4:1 impedance transformation when presented with a very wide range of termination impedances simply doesn't exist. Any "theory" that predicts it is oversimplified and invalid. Roy Lewallen, W7EL ------------ Roy, that is precisely what I said, but rather imprecisely. Ed, N2ECW |
loops and 4:1 baluns
Ed Cregger wrote:
Such things as variances in construction materials from one batch to another and the variations that one human will introduce to construction versus another human also induce characteristics that do not always jibe with theory. IMO, the major problem with baluns is that they are designed for specific impedances and most often used with unknown impedances. -- 73, Cecil http://www.w5dxp.com |
loops and 4:1 baluns
"Cecil Moore" wrote in message ... Ed Cregger wrote: Such things as variances in construction materials from one batch to another and the variations that one human will introduce to construction versus another human also induce characteristics that do not always jibe with theory. IMO, the major problem with baluns is that they are designed for specific impedances and most often used with unknown impedances. -- 73, Cecil http://www.w5dxp.com ---------- Very true, but often times they work well enough with varying impedances to get us on the air. If it is that or nothing, then I'm all for doing it. Ed, N2ECW |
loops and 4:1 baluns
Roy Lewallen wrote:
Ed Cregger wrote: I am beginning to suspect that traditionally made baluns are not as exact in practice as they are theoretically. This is not a surprise, really. Few things in electronics are exact as we humans like to assume, as you well know. Good seeing your post, OM. Ed Cregger, N2ECW former NM2K The whole problem is "liking to assume" that things are simpler than they are. When the theory you apply is too simple, guess what -- you'll find that the real thing doesn't behave as your oversimplified "theory" predicts. Theory works just fine, and accurately predicts how a real object will work. Oversimplified "theory" often doesn't work so well. A well made balun or RF transformer behaves reasonably well like an ideal transformer, that is, infinite winding inductance, no coupling capacitance, zero leakage inductance, no loss, and so forth, but only under quite a narrow range of circumstances. Those circumstances include being terminated with a fairly narrow range of impedances and over a limited frequency range. Usually, one side is designed to be terminated with 50 ohms, purely resistive. That means the other side of a 4:1 balun has to be terminated with something fairly close to 200 or 12.5 ohms (depending on how it's designed), also resistive, in order for it to work as intended. If the impedance differs very much at all from that value, you'll find that the transformation ratio is no longer 4:1, and that the balun will add a series and/or shunt impedance to the circuit. This can be accounted for by theory, but only with great difficulty since it requires careful characterization of the core and windings. People tend to design, and often test, a 4:1 balun in a 50 ohm environment, then attach it to a multiband antenna that has rather extreme (but entirely predictable) impedance variations. Then they're surprised because the impedance seen looking into the balun isn't 4 times or 1/4 times the antenna impedance, but is something wildly different. They shouldn't be. A 4:1 balun or transformer that effects a nice 4:1 impedance transformation when presented with a very wide range of termination impedances simply doesn't exist. Any "theory" that predicts it is oversimplified and invalid. Thanks for the information! Ed, good to run into you again! What brought you to Georgia? Ray - I found a Dover edition of Transmission Lines, Antennas and Waveguides. Thank you for the suggestion! One final question about the 4:1 balun: Assuming a single band Delta Loop with a feed point impedance of approx 100 ohms, with or without a 4:1 balun you have approximately a 2:1 SWR - so why use the balun? Thanks and 73, Tad Danley, K3TD |
loops and 4:1 baluns
"Tad Danley" wrote Ed, good to run into you again! What brought you to Georgia? Thanks and 73, Tad Danley, K3TD ---------- Dupont decided that they needed the wife in Chattanooga, TN. That was slightly over ten years ago. We are living in the Northwest corner of Georgia, just below Chattanooga, TN. It is a very, very nice place to live. What the heck are you doing in Texas? Ed, N2ECW |
loops and 4:1 baluns
Ed Cregger wrote:
Very true, but often times they work well enough with varying impedances to get us on the air. If it is that or nothing, then I'm all for doing it. When I was in high school, a ham came back to my "t-e-s-t-d-e-w-5-d-x-p" signal while my 40W Globe Scout was driving a 100W light bulb through 3' of wire on a table top. He gave me a 5x5 signal report. No balun required. :-) -- 73, Cecil http://www.w5dxp.com |
loops and 4:1 baluns
Tad Danley wrote:
One final question about the 4:1 balun: Assuming a single band Delta Loop with a feed point impedance of approx 100 ohms, with or without a 4:1 balun you have approximately a 2:1 SWR - so why use the balun? The resonant feedpoint impedance of a loop is often a little higher than 100 ohms, e.g. 115 ohms according to EZNEC, in which case a 4:1 balun will lower the SWR - sometimes alleviating foldback problems. -- 73, Cecil http://www.w5dxp.com |
loops and 4:1 baluns
Cecil Moore wrote:
Ed Cregger wrote: Very true, but often times they work well enough with varying impedances to get us on the air. If it is that or nothing, then I'm all for doing it. When I was in high school, a ham came back to my "t-e-s-t-d-e-w-5-d-x-p" signal while my 40W Globe Scout was driving a 100W light bulb through 3' of wire on a table top. He gave me a 5x5 signal report. No balun required. :-) http://palomar-engineers.com/1_1_Bal...alun_kits.html http://palomar-engineers.com/4_1_Bal...alun_kits.html |
loops and 4:1 baluns
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loops and 4:1 baluns
Tad Danley wrote:
I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD Tad: A 2:1 construction of a "true" 2:1 balun is possible, however, driving a 100 ohm loop from 50 ohm coax does NOT require one--meaning, a 2:1 "RF TRANSFORMER" will suit your purposes, more than adequately. The winding to the 50 ohm source will be half the turns of the 100 ohm winding--and there is no electrical connection between windings--i.e., the 50 and 100 windings are separate on the core. The turns will depend on the core material/power/freqs of your intended use ... However, the focus here is that you DO NOT need a true balun here, since the loop is inherently free from any adverse influences of using a voltage balun, a rf transformer is more than adequate for your use--and will simplify your requirements. You should find adequate construction data for a "2:1 rf transformer" (separate 50/100 ohm windings) with a google search ... etc. A ferrite bar or toroid, either, should fit your purposes, as you choose ... Regards, JS |
loops and 4:1 baluns
"John Smith" wrote in message ... Tad Danley wrote: I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD Tad: A 2:1 construction of a "true" 2:1 balun is possible, however, driving a 100 ohm loop from 50 ohm coax does NOT require one--meaning, a 2:1 "RF TRANSFORMER" will suit your purposes, more than adequately. The winding to the 50 ohm source will be half the turns of the 100 ohm winding--and there is no electrical connection between windings--i.e., the 50 and 100 windings are separate on the core. Usually the turns ratio of an impedance-matching transformer is the square of the impedance ratio. If the turns ratio, primary to secondary, is N the secondary voltage Vo is N times the primary voltage Vi but the secondary current Io is the primary current Ii divided by N. If the primary is fed from a source of impedance Zi, and Zi = Vi/Ii, then on the secondary side we have Zo = Vo/Io = NVi/(Ii/N) = (NxN)Vi/Ii. So Zo = (N^2)Zi or N = square root of (Zo/Zi). An impedance ratio of 2 would require a turns ratio 1.4. I wonder if there's a reason why this case would be different. Chris |
loops and 4:1 baluns
"christofire" wrote in message ... "John Smith" wrote in message ... Tad Danley wrote: I have started to experiment with EZNEC and am modeling a couple of loop antennas including some delta loops. I see references to hams using 4:1 baluns with these antennas, but the models I see show a feed point impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would help - what am I missing? Thanks and 73, Tad Danley, K3TD Tad: A 2:1 construction of a "true" 2:1 balun is possible, however, driving a 100 ohm loop from 50 ohm coax does NOT require one--meaning, a 2:1 "RF TRANSFORMER" will suit your purposes, more than adequately. The winding to the 50 ohm source will be half the turns of the 100 ohm winding--and there is no electrical connection between windings--i.e., the 50 and 100 windings are separate on the core. - - - - - - Usually the turns ratio of an impedance-matching transformer is the square of the impedance ratio. If the turns ratio, primary to secondary, is N the secondary voltage Vo is N times the primary voltage Vi but the secondary current Io is the primary current Ii divided by N. If the primary is fed from a source of impedance Zi, and Zi = Vi/Ii, then on the secondary side we have Zo = Vo/Io = NVi/(Ii/N) = (NxN)Vi/Ii. So Zo = (N^2)Zi or N = square root of (Zo/Zi). An impedance ratio of 2 would require a turns ratio 1.4. I wonder if there's a reason why this case would be different. Chris Ooops, I missed out the important word 'root' in my first line above! The impedance ratio is the square of the turns ratio. The turns ratio is the square-root of the impedance ratio. Chris |
loops and 4:1 baluns
John Smith wrote:
The winding to the 50 ohm source will be half the turns of the 100 ohm winding--and there is no electrical connection between windings--i.e., the 50 and 100 windings are separate on the core. Or it could be wound as an autotransformer. -- 73, Cecil http://www.w5dxp.com |
loops and 4:1 baluns
On Feb 7, 8:38*am, Cecil Moore wrote:
John Smith wrote: The winding to the 50 ohm source will be half the turns of the 100 ohm winding--and there is no electrical connection between windings--i.e., the 50 and 100 windings are separate on the core. Or it could be wound as an autotransformer. -- 73, Cecil *http://www.w5dxp.com I still prefer just a simple coax series transformer. As an example, for a 40m loop, about 22 ft of 75 ohm coax will do the trick. |
loops and 4:1 baluns
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loops and 4:1 baluns
On Feb 7, 4:46*pm, Cecil Moore wrote:
wrote: I still prefer just a simple coax series transformer. As an example, for a 40m loop, about 22 ft of 75 ohm coax will do the trick. But that wouldn't meet the 2:1 transformer requirement. -- 73, Cecil *http://www.w5dxp.com Should be pretty close. But calculating it, I show about 22.7 feet would be the best length for 7.150mhz. Assuming a 52 ohm feedline, and 75 ohm 1/4 wave section and a Zr of 120 ohms. I've used them before. Not really that critical on the precise length as long as it's pretty close. |
loops and 4:1 baluns
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