# Low frequency response

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Néstor Monedero on 23 Nov 2011
Answered: Sabin on 23 Jan 2024
Hi, I model a parallel RC circuit in Simscape. The circuit is excited by a random pulse signal. I need to obtain the frequency response of the circuit at low frequency (1-1000 Hz). How can i do it? Thanks in advance. Néstor
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Walter Roberson on 23 Nov 2011
Perhaps it is a tri-level signal, floating near ground between pulses that represented 0 or 1, with the values chosen at random. Or perhaps it is square wave but with random amplitudes. Or it could be a dual-level signal, 0 or 1, with the value held until the state changes, with an opportunity for state change at the given frequency.
I am thinking that if you have an RC circuit and you drive it with a constant periodic signal, that the circuit might end with a steady state or steady cycle that might not occur if the same circuit was triggered with the same basic pulse shape but with the state changing randomly. For example, the random signal could end up leading to a transient that might not be noticed with a periodic wave.
Néstor Monedero on 24 Nov 2011
Hi,
"a random pulse signal" is a signal where the pulses appear randomly on time. Pulses have the same amplitude (+10, -10 for example) and the width of the pulses are 1ms for example.I haven't model it yet, any idea?
I need to obtain (plot) the frequency response of the circuit (1-1000Hz).
Thanks,
Néstor

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### Answers (1)

Sabin on 23 Jan 2024
To obtain the frequency response of a parallel RC circuit in Simscape excited by a random pulse signal it is possible to save data and perform a Fast Fourier Transform using fft function after that. Or use a Spectrum Analyzer block.
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