High-resolution spectrogram around a known carrier frequency

[pegli]

Dear all,

I have trouble using the STFT spectrogram VI. I have a waveform which consists of multiple pulses at different frequencies. A mock-up waveform could be the following:

However, in reality the pulses have much closer frequencies, e.g. (4 GHz) and (4 GHz + 40 MHz). Since I know my carrier frequency (4 GHz) and the maximum offset that could occur, how can I limit the STFT spectrogram to look e.g. only from 3.9 GHz to 4.1 GHz?

I have created a little mock-up VI and attached it to this question. It seems I need to downconvert somehow but I can't really figure out how to do that.

Thank you very much for your help!

Peter

[Henrik_Volkers]

First : How about a first down mixing?

next: the frequency resolution of FFT is based on the signal duration ... 

how about:

detect and cut out the pulse

downmixing with carrier

a phase demodulation ..(IQ signals into arctan2, phaseunwrap) 

a frequency shift results in a ramp , detect and fit the ramp(s) ..  ?

Looking into RADAR papers ? 😉  I'm not a RADAR guy... but I work a lot with PM signals.. so that's my hammer on that nail 😄