
#1
Jun2013, 10:51 AM

P: 12

Hello
I don't know if this is the right place to place this, but here it goes: I tried an IDFT approach in LTspice, which doesn't know sqrt(1). If z=a+i*b then, in LTspice, z=a, z=a, so b is lost. With this in mind, the IDFT is done with sin^2+cos^2 which gives me sinc(x), but I need the sinc to be "regular" sinc, oscillating. So, the question is: is it possible through whatever trick/cheat/etc to restore or get an oscillating sinc(x) after the transform? Anything. I am using this chain of .funcs: real(n,t)=sin(2*pi*n*(tM/2)/(M+1))*f(n) imag(n,t)=cos(...) re(t)=real(0,t)+real(1,t)+... im(t)= ... h(t)=hypot(re(t),im(t))/(M+1) Anticipated thanks, Vlad PS: No homework,their time is long past. This is to try and implement a simple IDFT in LTspice. 



#2
Jun2113, 11:39 AM

P: 12

Unfortunately, I was in a hurry to fight a headache last night, so I mixed up: real(n,t)=cos(...), imag=sin. Also, the resulting impulse response can't be a result of a simulation, for example, I can't just use u(sinc1m) and then divide the pulses with a DFLOP  that would require simulating to find out the coefficients, then applying them to h[n], then running the simulation again.
A small test for if(abs(x)<wc,1,0) reveals it works, but it's still sinc (by the way, the title is actually sgn(abs(f(x))), f(x)=sinc(x), it was a really bad headache, apparently). To actually test the coefficients, I could use sgn(sinc(wc))*result, but that would only work for rectangular spectrum or one band only. So, there you have it, if anyone knows just a little bit, please let me know. Vlad 



#3
Jul613, 11:59 AM

P: 12

No need anymore, the discrete cosine/sine transforms do the trick.



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