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Bandpass filter the IQ data

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Hi,

 

How can I bandpass filter the baseband IQ data that is not centered around zero? It's either centered around a +ve frequency or a -ve frequency.

 

thanx 

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Hi Sandee,

 

You can do this a few ways. It looks like you are looking for a bandpass filter since a baseband filter by defination is centered at 0 and runns from -B to B as seen below:

 

File:Bandlimited.svg

 

Option 1 - Still centered around zero) If you are interested in the range from (+ or -) F1 (larger) -> F2 (smaller). You can work around this by using two filters. Just subtrack the F2 from F1. That should  give you the band pass that you are looking for.

 

Option 2 -  Still centered around zero) - Use a bandpass filter

 

Option 3 -  Adjust the spectral center by using scale vi in the signal processing -> Signal Operations pallete

 

With any luck this should help you do what you want. If not please post back and let us know

Joe Daily
National Instruments
Applications Engineer

may the G be with you ....
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Hi Joe,

 

I have acquired a band of 20 MHz IQ data at baseband (centered around 0 i.e the spectrum goes from -10MHz to +10MHz). This 20 MHz band contains 3 signals each of bandwidth 1MHz. Signal 1 is centered around frequency -6MHz, Signal 2 is centered around 0Hz and Signal 3 is centered around +4MHz. How can I filter Signal 1 i.e at -6MHz? since all the filters in DFD toolkit takes real signal as input and +ve cutoff frequencies.

 

thanx 

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Solution
Accepted by topic author SunJab
You can filter the I and Q separately (treat each as being real) and then combine them back as a complex number after filtering.
Randall Pursley
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Solution
Accepted by topic author SunJab

Sandee,

 

What you need to do is break it into three signals and seperate and shift each one. After that you can can then you can use the baseband filter to do what you need. 

Joe Daily
National Instruments
Applications Engineer

may the G be with you ....
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To sandee

Were you able to solve this problem? I have the same one.

Thanks.

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