Re: Smith Chart

Andy G4JNT

The  reply below from Mark was sent direct  :

Which is, more-or-less, what I can now recall being shown all those years ago.   It works for quarter wave transformers
Honour is satisfied and it appears that route was only ever a quick approximation for an impedance that had a mostly real component.

So there isn't an exact way of doing it - I felt all along it wasn't possible as a 'correct' Smith chart procedure!  At least without renormalising.
Much prefer calculation and software for microwave design than the manual Smith chart of old.

Andy  G4JNT

>sorry I cant reply to the list, I am away from home and don't have the correct email account set up
>In answer to the question, a slightly reserved yes
> simply place the rotation point  on the real axis   at the 50 ohm normalised value ( eg. rotate round 1.5 for 75 ohm >system on a 50 ohm chart)
> for  rotations that don't result in a large reactive transformed impedance this is really quite accurate (ie.1/4 wave >rotations and multiples of this)
>there is an increased error in both the displayed real and imaginary components with rotations further from the >centre and with those that result in points away from the real axis.
> there is a mathematical correction that can be applied, but that last time i looked at that was 35 years ago
> look up shifting the iconocentre
>hope that helps 

On 8 July 2016 at 11:52, 'brian.flynn@...' brian.flynn@... [ukmicrowaves] <ukmicrowaves@...> wrote:

Hi Andy,

I get involved in this a bit. I have always read off the
impedance/admittance and re-normalised. I have never come across the
procedure you suggest. I do this fairly regularly to design quarter wave
matching sections when the the impedances are not real.


Brian, GM8BJF.

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