To: |
tentec@contesting.com |
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Subject: |
Re: [TenTec] NEC, ground, grounds, and radials. |

From: |
"Dr. Gerald N. Johnson" <geraldj@weather.net> |

Reply-to: |
geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com> |

Date: |
Fri, 07 Jan 2011 16:44:09 -0600 |

List-post: |
<tentec@contesting.com">mailto:tentec@contesting.com> |

I've published the same article twice now, once in The VHF'er in 1966 and last year in the proceedings of the 2010 Central States VHF Conference. So I have it available on line but not in a format that will be found by search engines: http://www.geraldj.networkiowa.com/papers/CSVHF2010/lztl1.JPG http://www.geraldj.networkiowa.com/papers/CSVHF2010/lztl2.JPG I suppose I should work up an html page that could be found by a search engine and expand it with the history as I have found it. A fellow who knows the technical staff at ARRL has submitted it as a joint work to QST Technical Correspondence, but in 4 or 5 months there has been NO response from Newington. In my oral presentation at 2010 CSVHF, I presented some history of the topic. The inverse hyperbolic cosine formula is based on work of Harold Wheeler in about 1938 on the capacitance between closely spaced wires. He found that the charges were not distributed equally over the surface of the wires but are concentrated where the gap is smallest due to the higher electric field in that gap when the wire diameter is similar to the gap spacing. Something about in the gap the spacing is 3 times smaller than from the outside to the outside (neglecting the warp of fringing that has to accompany the field lines from outside to outside) makes the electric field 3 times stronger for the same potential difference. Makes much sense. So far the earliest publication I've found with the correct formula is the about 1942 "Reference Data for Radio Engineers" from Standard Telephone and Cables Ltd of London. Unfortunately the book has no copyright date and shows no references for cable impedances. The book was mostly copied into the 1943 "Reference Data for Radio Engineers" under Federal Telephone and Radio, Inc of New York (Both were associated with International Telephone and Telegraph Company) which is dated and acknowledges that ST&C source for much of the material. Unfortunately, about half the professional handbooks show only the 276 log formula that is only valid when the spacing is much larger than the conductor diameters but without that caveat. The impedance error is long about 1% in the 250 ohm region. It would appear Newington having been wrong for at least 68 years and three generations of technical editors is unwilling to admit error or that there can be any technical authority other than F.E. Handy. (long dead QST Technical editor). I plotted the curves in my article, because the inverse hyperbolic cosine is not a commonly tabulated function and isn't on many slide rules and calculators. I have seen one other formula that finagles with the diameter and spacing elements before doing the log function, but I've not checked it for accuracy. Its a bit more complex than the simple 120 inv cosh... formula. On 1/7/2011 3:20 PM, Steve Hunt wrote: > |

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