How to compute reflection coefficient from SPICE AC analysis

Could some electronics/SPICE guru please shed some light on this ? I was told that the reflection coefficient for a circuit, e.g., a L impedance transformer can be estimated from the frequency response plot of its SPICE AC analysis. If so, where could I get some details of the calculation steps. Thanks in advance.

Reply to
dakupoto
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Measure the source voltage and current, and use the definition of reflection, either in a SUBCKT, built from primitives, or as an expression in the postprocessor.

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They give it in terms of Z, do some algebra to get it in terms of node voltage and current.

Tim

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Reply to
Tim Williams

See "Return Loss and VSWR....." on the Simulation Tools & Macros Page of my website.

There is probably some way to do this with toiLTspice >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Jim Thompson

In message , snipped-for-privacy@gmail.com writes

It's related to VSWR

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You need to model a set of directional couplers ( say a current transformer) , to measure both forward and reverse voltage magnitude and phase. You might only need one for reflection only.

Some time ago I posted a simulation of a SWR Bridge on the LTSpice group which could plot VSWR as a function of frequency and by implication the reflection coefficient. You need a defined characteristic impedance - say 50ohms to make sense of it all.

Brian

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Brian Howie
Reply to
Brian Howie

Yeh that's it .

I put my circuit on alt.binaries.schematic.electronics ( I think!)

I was trying to work out how critical a 1/4 matching section 50/28 ohm was for length.

Brian

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Brian Howie
Reply to
Brian Howie

Many years ago I free-trialed some half-decent program called RFSim99 which could do this but I have no idea if it's even compatible with modern O/Ss. I think it was written for MSDOS!

No one mentions Smith charts any more. They were great for this type of thing, too.

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Cursitor Doom

I betcha 99.99% of the lurkers here can't work a Smith Chart :-(

I KNOW that 99.99% of the lurkers here can't do loop and nodal analysis. Otherwise we wouldn't see so many asinine circuit "suggestions". ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Reply to
Jim Thompson

Probably crap themselves at the sight of it! ;->

It's revealing when people like JL post their experiences of dealing with job candidates. What the hell do they teach in college these days?? :-(

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Cursitor Doom

Programming a uC and how to find "your" circuit in AoE :-(

99.99% DNH (do not hire). ...Jim Thompson
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| James E.Thompson                                 |    mens     | 
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Jim Thompson

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