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#12
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Anyway the difference in loss between #18 wire and RG-400 due to IR drop in the length of wire in a balun is too small to worry about. John Passaneau, W3JXP Penn State University ========================= Just like I said ! But a 1:1 choke balun has an indeterminate transformation ratio. |
#13
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On Thu, 22 Jan 2004 10:43:15 -0600, Cecil Moore
wrote: I use RG-400 teflon coax for my baluns. I've done that too, however, the other day I was made aware of teflon's problems with cold flow. You might want to look into that. Danny, K6MHE |
#14
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On Thu, 22 Jan 2004 15:30:52 +0000 (UTC), "Reg Edwards"
wrote: Figure-of-eight . . . . Two circles stuck together. Outline of plastic insulation surrounding a pair of close-spaced wires. Zip-cord ? --- Reg Apparently because when you separate the two at the thin part at one end, you can just zip it apart easily as far as needed. |
#15
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A 1:1 choke balun made out of coax "chokes" off current flowing on the
outside of shield, it has no effect on what is happing inside the coax between the inside of the shield and the center conductor. If you made a choke balun wound on a toroid or with beads with 2 foot of 75 ohm coax and used it on an antenna with a Z of 50 ohms at 28Mhz. That 2 foot of 75 ohm coax would transform the 50 ohms to 59.4+j21.3 ohms at the output end of your balun. If this is a problem it's up to the user to decide but I wouldn't like it. The same effect would happen if the balun was made with a parallel conductor line be it "zip cord" or enameled wire. If the Z of the line in the choke balun doesn't match the Z of the feed line it will cause an impedance transformation that will with vary with frequency. Of course if one is only using the balun at 7Mhz or lower it will not be as noticeable as it is at 28MHz. -- John Passaneau, W3JXP Penn State University "Reg Edwards" wrote in message ... Anyway the difference in loss between #18 wire and RG-400 due to IR drop in the length of wire in a balun is too small to worry about. John Passaneau, W3JXP Penn State University ========================= Just like I said ! But a 1:1 choke balun has an indeterminate transformation ratio. |
#16
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When connecting a 50-ohm circuit to a 600-ohm line via a choke balun it
makes no difference what the impedance of the short length of line forming the choke might be. For practical purposes the severe mismatch is due entirely to the difference between 50 and 600 ohms. One must avoid suffering from delusions of accuracy. --- Reg |
#17
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That's true but sometime we use current baluns in 50 ohm systems and one
should be aware of what happens to the Z when the line in the balun is some random impedance. I've done some tests on various types of baluns looking at balanced to unbalanced conversion verses frequency and losses and I like 3 to 4" diameter toroids with a mu of 100 to 200 wound with Teflon coax. Most of my antennas are close to 50 ohm and I don't need any unwanted impedance transformations. -- John Passaneau W3JXP State College Pa This mail is a natural product. The slight variations in spelling and grammar enhance its individual character and beauty and in no way are to be considered flaws or defects. "Reg Edwards" wrote in message ... When connecting a 50-ohm circuit to a 600-ohm line via a choke balun it makes no difference what the impedance of the short length of line forming the choke might be. For practical purposes the severe mismatch is due entirely to the difference between 50 and 600 ohms. One must avoid suffering from delusions of accuracy. --- Reg |
#18
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wrote in message
... On Thu, 22 Jan 2004 15:30:52 +0000 (UTC), "Reg Edwards" wrote: Figure-of-eight . . . . Two circles stuck together. Outline of plastic insulation surrounding a pair of close-spaced wires. Zip-cord ? --- Reg Apparently because when you separate the two at the thin part at one end, you can just zip it apart easily as far as needed. ======================== There are two varieties. One lays down flat on a flat surface. The other has a twist, a lay, in it. Only the first should be used for baluns. If either is described as 'zip-cord' then there is ambiguity. Which is why I described describe the cord used for baluns as 'figure of eight'. But I suppose an ambiguity still remains. --- Reg. |
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