Yes, ACOSH has the LOG approximation you show which is good
if you meet the restrictions. There is also a way to replace
the ACOSH function with a more complicated expression involving
LOG that is an exact equivalent. However, this is not worth
bothering with now that you can just type ACOSH on a scientific
pocket calculator or your windows calculator (switch to scientific
mode). (I have a complete set of all editions of RDRE, but just grabbed
one at random. It is interesting to see how they evolved).
Rick N6RK
Bob Nielsen wrote:
> On Apr 17, 2008, at 9:53 PM, Richard (Rick) Karlquist wrote:
>
>> It is in Reference Data for Radio Engineers, Chapter 24,
>> configuration N.
>>
>> Zo = [60/(epsilon^.5)]* ACOSH {[4D^2/d1d2 - d1/d2 -d2/d1]/2}
>>
>> where epsilon is relative dielectric constant
>> D is center to center spacing
>> d1 and d2 are the wire diameters
>> ACOSH is inverse hyperbolic cosine
>>
>> Of course I wonder why would anyone deliberately use different
>> diameters?
>>
>
> Hmm, it's different in my copy (4th edition (1956), chapter 20):
>
> (276/(epsilon^.5) * log10 (2D/(2*d1d2)^.5) for d1, d2 << D
>
> I suspect (but haven't checked) that the formula Rick gave may be
> more general (without the d1, d2 << D restriction).
>
> Bob, N7XY
>
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