Re: [Help-gnucap] (no subject)

[Karl Hammar]

Sorry for previous mail, it got avay too early.

Al Davis:
> On Sunday 07 April 2013, Karl Hammar wrote:
> > I get different volt calculated vs. measured in node 2 of
> > simulation below. Can anyone point to where my mistake is?
> > 
> > It should be 0.5 V for 50 Ohm input impedance but only
> > measures to less than 200 mV. Replacing circuit 50 Ohm BNC
> > terminator gives me the correct 500mV.
> > 
> > My stuff is available in:
> > 
> >  http://turkos.aspodata.se/git/openhw/rfid/
...
> My guess at where the mistake is ..  something you haven't shown 
> us.

Yes, isn't that the way it usually is.

I have a function generator, koax to scope, bnc-t to anenna pcb,
and I get better values now. So Im' kindof satisfied, but still
have to learn gnucap better.

...
> Gnucap 2009.12.07 RCS 26.136

We seems to have differnt versions, I'll try to get the same as yours.

> .....
> gnucap> spice
> gnucap-spice>C1a  2 4 7.39e-10
> gnucap-spice>C1b  0 3 7.39e-10
> gnucap-spice>C2   2 0 1.65e-09
> gnucap-spice>Cpar 4 3 1e-11
> gnucap-spice>L    4 3 4.4e-07
> gnucap-spice>Rpar 4 3 1500
> gnucap-spice>.print ac z(2) zp(2) zr(2) zi(2)
> gnucap-spice>.ac 12meg 14meg 10k
> #Freq       z(2)       zp(2)      zr(2)      zi(2)     
...
>  12.33Meg   0.82071   -1.8369     0.82028   -0.026307  
>  12.34Meg   0.83455    2.1224     0.83398    0.030907  
...
>  13.6Meg    50.85     -11.238     49.875    -9.9101    
>  13.61Meg   50.855    -14.512     49.233    -12.743    
>  13.62Meg   50.694    -17.73      48.286    -15.438    
...

Good point.

How did you manage to get the value 50, should one not include
the signal source or can one leave that out?

...
> It's interesting that zero-phase occurs at a different frequency 
> than max voltage or max impedance.

Probably because the sought resonance is over the inductor and
at the connector we see a C2 paralell  with 2*C1a + L//Rpar.

> Your use of the "generator" keyword is probably not what you 
> want, but that is not the problem here.  Since you specified an 
> AC value, it overrides the "generator" making it apply only to 
> transient analysis.

Sorry, but I'm new to gnucap. I got that when I run

 gnetlist  -g spice test.sch

I have since deleted that file and it's output since it did not
have a node 0 and gave strange results when running the simulation.

Regards,
/Karl Hammar

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