Correct!
I believe it was Jerry who pointed me to the accurate formula a couple
of years ago on this very List. I was considering how to build low
impedance balanced line with a Zo in the range 50 Ohms to 70 Ohms for a
Hexbeam application. One look at the published curves told me it
couldn't be done; but Jerry put me right!
Steve G3TXQ
On 08/01/2011 02:05, Dr. Gerald N. Johnson wrote:
> Like my curves its center to center. The upper trace is using the 276
> log formula and the lower one is the 120 inv hyperbolic cosine function.
> Mine has the spacings on a log scale his is a liner scale. The upper
> trace formula is increasingly inaccurate below 300 ohms impedance with
> 87,000 percent error at a spacing just a hair wider than the conductors
> touching. The wrong formula says you can't get a Z0 less than 87 ohms
> (as published in QST last summer again), but the correct formula gets
> down to practically zero Z0 just before the conductors make contact.
> http://www.geraldj.networkiowa.com/papers/CSVHF2010/lztl1.JPG/
> http://www.geraldj.networkiowa.com/papers/CSVHF2010/lztl2.JPG/
>
> 73, Jerry, K0CQ
>
> On 1/7/2011 7:46 PM, Jack Mandelman wrote:
>> Steve,
>> In your plot how are you defining S, the spacing between conductors? Is it
>> center to center? Is it consistent for both the approximated and actual
>> curves? It appears that only the actual curve uses the center to center
>> definition; in the limit as S-->d the inner edge to inner edge spacing goes
>> to zero, and Zo also goes to zero.
>>
>> Jack K1VT
>>
>>> Jerry,
>>> A picture paints a thousand words:
>>> http://www.karinya.net/g3txq/temp/ladderline_zo.png
>>> 73,
>>> Steve G3TXQ
>>> On 07/01/2011 22:44, Dr. Gerald N. Johnson wrote:
>>>> / 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./
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