USRP Frequency Translating FIR Filter

[SigurdAB]

Hi,

I would like to use the USRP as a Software Defined Radio where I can sample a wide spectrum (like 20MHz) and then chose to demodulate a small part of the received spectrum. An example is to sample the whole FM radio band from 88MHz to 108MHz and then from these data FM demodulate 200kHz from a station on 103.9MHz or any other selected signal.

With GNU radio I believe this can be performed by a function called Frequency Xlating FIR Filter which can transform the zero frequency of the IQ data, add a FIR filter and then decimate the data. With LabView I have tried several filters, decimations and transformations but I never end up getting a good output.

Can anyone guide me in the right way on how I can do this?

With regards,

-Sigurd A.

[YYYs]

I am not sure, but maybe MT Downconvert Passband.vi might help you?

[kc95]

Hi,I am also very interested in it, could you provide us with some methods? Thank you!

[Sigurd]

Hi,
I forgot to update this post. I did not find any VI which did this but after some studying and trials I found something that seems to work OK for me. See attached picture.

The clue was to multiply the IQ data with a sinus signal with frequency equal to the frequency shift, and with same sample rate and number of samples as the IQ signal.
Then the signals can be decimated to the wanted bandwidth.

With regards,
Sigurd A.

[peter.go]

Hello, I working in something similar. I have a IQ signal with 2.8 MHz of BW and I need filter a channel of 200kHz of BW, but when I applied a LPF, it not working well and I see in the spectrum frecuency components in the range 0-200kHz and 2.6-2.8Mhz, I need resolve this problem.