when I apply a 1Khz signal, why after DFT, I get the first harmonic at 833Hz

[evil1949]

Hi All,

I apply a sine wave (1KHz, vp=400mA) in series with a dc source to my DUT. When I use the function of DFT in calculator to plot the spectrum at the input, I see a harmonic at 833Hz; and the frequency interval is 833Hz, why is that? For the DFT function, I do like this : dft( vin 0.2u 1.2m 1024 "rectangle" 1 1)

 

[std_match]

1.2m = 1200 us

1200 - 0.2 us = 1199.8 us = 1/(833.47 Hz)

A rectangular window will almost certainly create it's own frequency, regardless of the input signal.

 

[evil1949]

1.2m = 1200 us

1200 - 0.2 us = 1199.8 us = 1/(833.47 Hz)

A rectangular window will almost certainly create it's own frequency, regardless of the input signal.

OMG! thanks a lot!!! it is a really stupid mistake unitl you point out....... I apply the sine wave a at 0.2ms!!. thanks