How to design the measurement system to generate chirp signal on carrier frequency of 2.4 GHz ?

[bellaaa]

Hi all,

I have tried to design the measurement system to generate chirp signal on carrier frequency of 2.4 GHz as shown as in Figure "chirp.jpg". I want to design chirp signal with measurement bandwidth of 40 MHz and time of 100 ns using USRP N210 as transmitter and NI-2922 as receiver, but it did not work yet.

While I have set some parameters such as :
1. Tone frequency 1 : 2.39 GHz
2. Tone frequency 2 : 2.43 GHz
3.. IQ rate : 4.86 GHz (But, it did not work. And the coerced IQ rate is set to be 50M. Does it maximum value of USRP device?)

And the result did not show as chirp signal. Does anyone ever design chirp signal with 2 tone frequency in the carrier frequency of 2.4 GHz ? And i want to yield measurement bandwidth of 40 MHz and time of 100 ns.

Thanks

[Case_in_Point · Accepted solution]

Hi bellaaa,

Generating a chirp should be pretty simple, what part are you having difficulty with? Using LabVIEW to generate the array of data, or is it more on the USRP parameters as you mentioned? For the mechanics of making a chirp signal, there is a nice KB on this: http://digital.ni.com/public.nsf/allkb/711B320F50C863E3862573D400625F3E.

Regarding your parameters, I did want to make a note on the IQ rate. Your IQ rate should be set in terms of your modulation rate, not the overall frequency. So generating a tone at 2.43 GHz on a carrier frequency of 2.4 GHz only requires an IQ rate of 30 MHz. You actually want an IQ rate a little higher than your modulation frequency, although note that you do not have to fulfill Nyquist criteria and hit 2x your frequency. Since you're overall modulation frequency spectrum runs from 2.39 GHz to 2.43 GHz, that's 40 MHz of bandwidth, which a 50 MHz IQ rate should be sufficient to handle. 

Regards,

Cason

NIC AE