I write a simple low pass filter, 1VAC on input:
vac in 0 ac 1
r in out 1000
c out 0 0.000001
.ac dec 100 10 10000
I expect that output signal is 0.7 when frequency is 159Hz (f3dB=1/(2piRC)), but on the ac simulation this is 105Hz. I've got this results on ngspice-24 and ngspice on-line, pspice shows correct result (amplitude 0,7 with 159Hz). Transient analysis with sinus in ngspice also gives correct result. I suppose sth is wrong with .ac analysis. It works strangely also with other circuits I've simulated, the same simulations on pspice looks ok.
My operating system - linux mint 11.
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