thinking of buying

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tandersn
Posts: 4
Joined: Tue Aug 04, 2020 9:25 pm

thinking of buying

Post by tandersn » Tue Aug 04, 2020 9:43 pm

Hi, i am interested in 125/10 & 125/14. Before purchasing, is it possible to save a RAW RF capture file to the SD card? I am working on a project that requires 40Msps and covers the spectrum 0(DC)-15MHZ. The processing i wish to do can't be done in real-time on my computer, so i want to just capture raw data and save to file, then transfer to computer for offline processing.

thanks.

alex123go
Posts: 14
Joined: Mon May 04, 2020 4:46 pm

Re: thinking of buying

Post by alex123go » Wed Aug 05, 2020 8:30 pm

Hi,

The bandwidth of the Red Pitaya ADCs is 40Mhz for the 125-10 and 50MHz for the 125-14, So for the 0-15MHz bandwidth, you'll always be OK as long as you sample at twice the higher frequency you want to acquire. Therefore, acquiring at 30MHz or higher is ok (although 30MHz might be borderline for aliaising).

Then, the next question is how long do you want to record the data.

1 : With the original oscilloscope application, you can acquire up to 16k samples. It seems like you can only control the sampling rate by zooming the x axis, but if you arrange thing correctly you'll probably be able to have something close to 40MHz.

2 : There is the ddr_dump firmware from Nils Roos. I haven't use it a lot, but you can continuously stream the data over an ethernet cable or save them in a file on the RP. You can also decimate the sampling rate by a power of 2. So you'll have 62.5 MHz or 31.25Mhz. Both could fill your requirement, but the choice would depend on the risk of aliaising vs how long you want to record (if streaming is/is not possible at these data rate, I don't remember the actual limit). I also think you can average data if you decimate, which is good to reduce impact of aliaising.

3 : I just finished a firmware where you can acquire up to 200M samples at full speed (125MHz) (which is 1.6 sec in single channel mode) and transfer them directly at your computer via an oscilloscope-like GUI or a script without gui. It's available at https://github.com/alex123go/RedPitaya_Acquisition.

I think option 2 or 3 would be best for you.

Also remember, you can always resample in post-processing to reduce the size of the data you have to process.

tandersn
Posts: 4
Joined: Tue Aug 04, 2020 9:25 pm

Re: thinking of buying

Post by tandersn » Sat Aug 08, 2020 2:21 am

Thanks! I just ordered one.

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