Re: S - Y Parameter conversion with Smith Chart

From: John Woodgate (jmw_at_jmwa.demon.contraspam.yuk)
Date: 08/01/04 

Date: Sun, 1 Aug 2004 06:38:31 +0100

I read in sci.electronics.design that Activ8 <reply2group@ndbbm.net>
wrote (in <1kpirajws18ml$.dlg@news.individual.net>) about 'S - Y
Parameter conversion with Smith Chart', on Sun, 1 Aug 2004:
>On Sun, 1 Aug 2004 02:19:02 +0000 (UTC), Reg Edwards wrote:
>
>>> Could you please explain that a bit more? The chart is a graphical way
>>> of doing mathematics. Where does frequency enter the picture?
>
>Reaactance depends on it. I must not understand your question.

Reg wrote that the Smith Chart doesn't work at low frequencies. Since
it's just a way of solving equations, it can't fail to work. What
'fails' is that at low frequencies, either different equations apply
(no) or different terms in the equations become significant (yes).
>>>
>>> If you mean that the characteristic impedances of 'transmission lines'
>>> at low frequencies aren't resistive, I quite agree.
>>> --
>> =================================
>>
>> The characteristic impedances of ALL practical lines aren't resistive.

Well, yes, but at high enough frequencies, the reactive term is small.

Zo^2 = (R + jwL)/(G + jwC)

For high enough w (omega), provided R (series resistance) and G (shunt
loss resistance) are low, Zo^2 = L/C.

> But
>> your statement just about sums up the situation.

You agree with my explanation above, that it's not the chart that
'fails', but that terms in the equations change significance at low
frequencies? 

-- 
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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