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ham_radio:semi_rigid_cable [2013/01/08 19:00] (current)
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| | ====== Semi Rigid Cable ====== |
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| | //On Tuesday 29 January 2008 15:07, Richard Gill wrote:// |
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| | //A few years ago I bought some Semi-Rigid Coax from out favorite bid site for later use. I am building some Yagi's as described in the Aug 2006 QST article by Jim, W6PQL. The yagi's use a piece of UT-141 Semi Rigid coax as a balun. The coax I have has no ID or number and does not look like the coax in the article. Anyway the coax I have has the follow specs: appears to be made of Copper tube.// |
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| | //Has a OD of .141"// |
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| | //ID of .120" ~// |
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| | //Insulator is a white plastic looking material.// |
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| | //Center Conductor is solid wire. 20Gauge (.0365" Dia) and may be silver wire. Not Copper.// |
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| | //Each Piece has a SMA Connector soldered on the end.// |
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| | ---- |
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| | Steve VE3SMA replied: |
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| | It looks like the right stuff. UT-141 is one manufacturer's name for what is more generally known as MIL-C-17/130-RG402, which has .141" OD (bare copper), .119" OD PTFE insulation and .036" diameter inner conductor (silver plated copper-covered steel). |
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| | There are many similar variants with different outer conductor materials, etc. |
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| | The impedance formula should be |
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| | Zo = ( 138/SQRT(e) ) * log(D/d) |
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| | where SQRT(e) means "square root of the dielectric constant" and the log is the base 10 type. It comes out to 49.4 ohms using the above dimensions and e = 2.1 which is what my reference gives for PTFE. |
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| | 73, |
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| | Steve VE3SMA |
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