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Re: rochester (belated) transmission line...
Hi Dave and everyone,
On Tx lines you wrote...
> I have not reread any of my Corum lately. If sqrt (l/c) is based
> on the usual formula for a transmission line, there is a gotcha.
>
> sqrt(L/C) is a SIMPLIFIED VERSION. some references do not point
> this out. The full form (from memory) is more like SQRT ((L+R)/(C+g)).
> R is the series reistance (per unit length in tx line work).
> g is a 'conductance' related to resistive leakage thru the insulation.
>
> For the USUAL range of RF intrest (say 500KHz to 500GHz) the R is so
> small relative to the Xl and the g is so 'small' realtive to XC that
> the simplified form works out. (Yeah. I switched for L to XL. Bear
> with me...). AS THE FREQS GO DOWN, THE SIMPLIFIED FORM BECOMES
> PROGRESSIVELY LESS ACCURATE. (I had cause some years ago, to
> xperimentally verify this. got paid for it. NOT new knowledge,
> tho. First recognized at the turn of the century....)
I realize there are simplifications in the L/C thing. Interestingly,
Schelkunoff doesn't take the distributed parameters into account
either. It simply derives a value from the geometry of the system.
In general, the answers are comparable in a lot of cases but I do
wonder about using formulae that are right in only some situations.
It'd be nice if one or other was applicable to the lot.
Malcolm