Why this block diagram for USRP does not generate FMCW Chirp signal?

[firstking]

I am trying to generate chirp signal to create fmcw radar system. My USRP is N210 with SBX daugtherboard. If I am not wrong fmcw is simply a frequency modulated wave. Thus, with a message signal I should change the frequency of the output signal.

My desire is to output a signal with center frequency of 750MHz. I think the frequency deviation should be maximum of 20MHz beacuse of the 40MHz limited BW of the HW. Right?

The thing is, I am not sure how the FM block works. There is no input to the block about the carrier wave. Thus, what is the modulated signal and properties of it. What should be the required IQ rate and mesage signal frequncy and magnitude also.

Can you please give me some information about how usrp outputs this.

[vvkakade · Accepted solution]

Hi,

You might find the Chirp Pattern GVI helpful:

http://www.ni.com/documentation/en/labview-comms/1.0/node-ref/chirp-pattern/

Also if you are using LabVIEW:

http://zone.ni.com/reference/en-XX/help/371361H-01/lvanls/chirp_pattern/

[firstking]

Hi, thank you. I couldn't find the chirp signal generator in Design Suite 2.0. Is that only included in 1.0?

[Mihai_Liviu · Accepted solution]

You can implement the chirp block yourself, using basic vi-s. You can see a suggestion in the next picture:

[firstking]

So is this the IQ signal which will be fed into USRP Write TX block? How will I load this into carrier and output from TX port as RF?

[Mihai_Liviu · Accepted solution]

I am not familiar with the software you use, Labview Communications. The block suggested above outputs the I and Q components of the baseband version of the chirp. You can transform it in a complex signal (using Re Im to complex vi) and feed it to the TX block (I don't know which one is that in your project). The TX block should also have the carrier frequency, power, sample rate etc. as inputs.

[firstking]

Yes, the carrier frequency, gain, and sampling information is provided to USRP which configures TX accordingly. Thanks, I will try it when I go back to the lab on Wednesday.