|
Folded Dipole Calculator Help
Hi All,
I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike |
Folded Dipole Calculator Help
amdx wrote:
Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike Hi, The eq. seems right. Folded dipole is basically a loop. Usually we use 300 Ohm feeder. Tony VE6CGX |
Folded Dipole Calculator Help
Tony Hwang wrote:
amdx wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike Hi, The eq. seems right. Folded dipole is basically a loop. Usually we use 300 Ohm feeder. Tony VE6CGX Hi, And you can use a tranformer 300 Ohm to 75 Ohm to use coax if need. It becomes a from 300 Ohm balaanced to 75 Ohm unbalanced feed. |
Folded Dipole Calculator Help
On Sat, 14 Nov 2009 12:05:21 -0600, amdx wrote:
Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic_Notebook/antennas/ folded_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike The way I read it is that you put in the feed impedance that a similar- length plain-ol' dipole in the same situation would have. In a Yagi this can be significantly lower than 72 ohms, which is the whole reason you're considering a folded dipole. Does the author have contact information? Perhaps you could ask the source? -- www.wescottdesign.com |
Folded Dipole Calculator Help
"Tony Hwang" wrote in message ... amdx wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike Hi, The eq. seems right. Folded dipole is basically a loop. Usually we use 300 Ohm feeder. Tony VE6CGX In what case would I alter the 72 ohms? Mike |
Folded Dipole Calculator Help
"Tony Hwang" wrote in message ... amdx wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike Hi, The eq. seems right. Folded dipole is basically a loop. Usually we use 300 Ohm feeder. Tony VE6CGX In what case would I alter the 72 ohms? Mike |
Folded Dipole Calculator Help
On Sat, 14 Nov 2009 12:05:21 -0600, amdx wrote:
Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic_Notebook/antennas/ folded_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike I've seen older Yagis that use folded dipoles, but the newer ones seem to lean more toward gamma or T matches. You get more latitude for adjusting impedance, in the gamma case you get a kinda sorta good match to coax without a balun, and if you're employing plumber's delight construction it's no more difficult to fabricate than a folded dipole. So why a folded dipole, pray tell? -- www.wescottdesign.com |
Folded Dipole Calculator Help
On Sat, 14 Nov 2009 12:05:21 -0600, "amdx" wrote:
Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. Excuse me, but what does such simple dipole calculator have to do with the calculations for a Yagi feed element ? Even assuming a single element feed element antenna, playing with the tube diameter (upper and lower bars) or the number of bars in a folded dipole will radically change the feed impedance. Paul |
Folded Dipole Calculator Help
"Paul Keinanen" wrote in message ... On Sat, 14 Nov 2009 12:05:21 -0600, "amdx" wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. Excuse me, but what does such simple dipole calculator have to do with the calculations for a Yagi feed element ? I think it all started with the MFJ-1800 that uses a folded dipole, but there are many yagis that use a folded dipole as the driven element. But, I think (now) I understand enough to know why you ask the question. I think your point is the impedance of dipole feed on a yagi is highly modified by the reflector and directors. Even assuming a single element feed element antenna, playing with the tube diameter (upper and lower bars) or the number of bars in a folded dipole will radically change the feed impedance. Paul I excerpted this from my latest email to my friend I'm having the disagreement with. (Might not even be a disagreement, it could be a miscommunication.) Excerpt; "The online calculator takes the (Impedance of a dipole x Ratio). This gives you the impedance after folding the dipole. We still have no idea what the impedance of a dipole is when surrounded by the reflector and director. We do know how to change the transformation ratio once we know what the impedance of dipole would be in that surrounding." Mike |
Folded Dipole Calculator Help
amdx wrote:
"Paul Keinanen" wrote in message ... On Sat, 14 Nov 2009 12:05:21 -0600, "amdx" wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. Excuse me, but what does such simple dipole calculator have to do with the calculations for a Yagi feed element ? I think it all started with the MFJ-1800 that uses a folded dipole, but there are many yagis that use a folded dipole as the driven element. But, I think (now) I understand enough to know why you ask the question. I think your point is the impedance of dipole feed on a yagi is highly modified by the reflector and directors. Even assuming a single element feed element antenna, playing with the tube diameter (upper and lower bars) or the number of bars in a folded dipole will radically change the feed impedance. Paul I excerpted this from my latest email to my friend I'm having the disagreement with. (Might not even be a disagreement, it could be a miscommunication.) Excerpt; "The online calculator takes the (Impedance of a dipole x Ratio). This gives you the impedance after folding the dipole. We still have no idea what the impedance of a dipole is when surrounded by the reflector and director. We do know how to change the transformation ratio once we know what the impedance of dipole would be in that surrounding." Mike The nominal impedance of a dipole in free space is approximately 72 ohms. If it is part of a system its impedance will be influenced by that system causing it to change from nominal. Folding the dipole allows it to behave as a transformer ! Thus the nominal dipole impedance can be altered to a value that can more easily be matched to the feed line. Commonly the impedance of a dipole that is part of a system. ie "Yagi" falls to a much lower value. Under these conditions the folded dipole can be used to raise the impedance seen at the feed point to a more usable value. Someone mentioned "Gama match". Whilst symmetrical gamma matches can be used, single ended is popular because it is inherently unbalanced and can be easily matched to a co-axial feedline. -- Best Regards: Baron. |
Folded Dipole Calculator Help
amdx wrote:
"Tony wrote in message ... amdx wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike Hi, The eq. seems right. Folded dipole is basically a loop. Usually we use 300 Ohm feeder. Tony VE6CGX In what case would I alter the 72 ohms? Mike Hi, Feed point impedance becomes near that when it is just a dipole(not folded). On a haf wave element at center feed point the current and voltage phase is such that the impedance is near that figure. If it is vertical uater wave whip, the other half mirror image is prjected into the ground forming dipole and in that case feed point impedance at the bottom is around 50 Ohm. I am old dinosaur EE(class of 60), my brain is not as bright as it used to, LOL! |
Folded Dipole Calculator Help
Tim Wescott wrote:
On Sat, 14 Nov 2009 12:05:21 -0600, amdx wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic_Notebook/antennas/ folded_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike I've seen older Yagis that use folded dipoles, but the newer ones seem to lean more toward gamma or T matches. You get more latitude for adjusting impedance, in the gamma case you get a kinda sorta good match to coax without a balun, and if you're employing plumber's delight construction it's no more difficult to fabricate than a folded dipole. So why a folded dipole, pray tell? Hi, Also folded dipole tends to have broader b/w compared to dipole. |
Folded Dipole Calculator Help
amdx wrote:
"Paul wrote in message ... On Sat, 14 Nov 2009 12:05:21 -0600, wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic...ed_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. Excuse me, but what does such simple dipole calculator have to do with the calculations for a Yagi feed element ? I think it all started with the MFJ-1800 that uses a folded dipole, but there are many yagis that use a folded dipole as the driven element. But, I think (now) I understand enough to know why you ask the question. I think your point is the impedance of dipole feed on a yagi is highly modified by the reflector and directors. Even assuming a single element feed element antenna, playing with the tube diameter (upper and lower bars) or the number of bars in a folded dipole will radically change the feed impedance. Paul I excerpted this from my latest email to my friend I'm having the disagreement with. (Might not even be a disagreement, it could be a miscommunication.) Excerpt; "The online calculator takes the (Impedance of a dipole x Ratio). This gives you the impedance after folding the dipole. We still have no idea what the impedance of a dipole is when surrounded by the reflector and director. We do know how to change the transformation ratio once we know what the impedance of dipole would be in that surrounding." Mike Hi, Even now Yagi-Uda antenna design is empirical business tinkering with it in the antenna range based on theory plus actual field result. |
Folded Dipole Calculator Help
Tony Hwang wrote:
Tim Wescott wrote: On Sat, 14 Nov 2009 12:05:21 -0600, amdx wrote: Hi All, I'm having a disagreement about the use of this folded dipole calculator impedance calculator. http://www.k7mem.150m.com/Electronic_Notebook/antennas/ folded_dipole.html We are using it to calculate the impedance of folded dipoles to drive a yagi. When entering data it asks for "Simple dipole feed impedance (ohms)" Default is 72 ohms. This assumes a 1/2 wave dipole. The fellow I'm disagreeing with say's, "the reason that the variable in the calculator for the "dipole feed impedance" could be if you want to transform the z to something else, such as 50 ohms." I don't even understand what he means. I can only think of one reason to alter the 72 ohms, that would be if you use a a different length folded dipole. I'll readily admit the other fellow knows more about this than me, but I need more convincing :-) Can anyone explain this to me. Thanks, Mike I've seen older Yagis that use folded dipoles, but the newer ones seem to lean more toward gamma or T matches. You get more latitude for adjusting impedance, in the gamma case you get a kinda sorta good match to coax without a balun, and if you're employing plumber's delight construction it's no more difficult to fabricate than a folded dipole. So why a folded dipole, pray tell? Hi, Also folded dipole tends to have broader b/w compared to dipole. Due to the transformer effect of folding it. -- Best Regards: Baron. |
Folded Dipole Calculator Help
Also folded dipole tends to have broader b/w compared to dipole.
Due to the transformer effect of folding it. Most of the bandwidth enhancement on a folded dipole comes from the fact that it's a "fatter" radiator rather than because it's folded. Section Bii) he http://www.karinya.net/g3txq/folded_dipole/ Steve G3TXQ |
Folded Dipole Calculator Help
"steveeh131047" wrote in message ... Also folded dipole tends to have broader b/w compared to dipole. Due to the transformer effect of folding it. Most of the bandwidth enhancement on a folded dipole comes from the fact that it's a "fatter" radiator rather than because it's folded. Section Bii) he http://www.karinya.net/g3txq/folded_dipole/ Steve G3TXQ Of course, the 'transformer effect' is unlikely to increase the bandwidth by itself, and when the common type of half-wave-line balun (and 4:1 impedance transformer) is used to connect the dipole to co-axial cable the resonant nature of this additional half wavelength is likely to impair the bandwidth to some extent (by introducing additional reactance at frequencies for which its length isn't a true half wavelength). Certainly the additional fatness of the folded-dipole structure must contribute to improved bandwidth by reducing the slopes of the terminal resistance and reactance, but the treatment given in the link provided above - suggesting that the susceptance added at the drive point by the 'parasitic' parallel wire or rod, joined to the driven element at its ends, has insignificant effect - is a rather broad generalisation which may not be true for some geometries (i.e. length/thickness ratios of the wires/rods and their spacing). Generally, it's dangerous to generalise! There's quite a lot going on in a folded dipole. Some further insight (on allied, but not the same, topic) is offered in http://www.physics.princeton.edu/~mc...cutantenna.pdf. Chris |
| All times are GMT +1. The time now is 10:29 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com