Greetings,

I was wondering if anyone is familiar with utilizing the FFT block from the
Ettus code library. I am using the default binary that is complied
following the instructions in [1]. I have a working environment and have
successfully used the foshpor window in the end example of that install to
look at the spectrum around my area, which was really cool. I had some old
hackRF examples I had made when I went through that course and was trying
to convert them over to run on the E312, which some changes. I started with
building a radio using the UHD software components but found out real quick
that A9 can not sample fast enough, so switch to slowly using the RFNoC
blocks, like Radio, FIFO, FFT, to do the heavy lifting, with a ZMQ Push to
my host where it does software processing on it. Right now its just meant
to be an FM radio, like in your car, and I have copied many of the modules
over from the fosphor example in the gr-ettus install examples folder.

With that bg, I get an interesting result. With the components of Window
and FFT disabled I get an audio output. When I don't the host shows on the
QT GUI a sync at my centering frequency. I assumed it was b/c the RFNoC
blocks were operating with a 512 vector size and GNU Radio software blocks
prefer a vector size of 1 (for some of them like QT GUI). I also thought it
was b/c the QT block also has an FFT, so I placed an inverse FFT inline,
which had no effect.

With all this said, I know there needs to be an FFT to process an analog
signal, that is how a DFT is handled with logic or computers. I would like
to do the heavy lifting on the FPGA with its FFT, rather than relying on
the FFT in the gui, and also still get audio out. Does anyone have an
suggestions, and are there any reference materials that could be
recommended? I have mostly been using Google and examples I can find on the
Ettus KB, plus the gr-ettus installed examples as references.

I have attached my .grc files for reference.

Regards,
Jon Lockhart

[1]
https://kb.ettus.com/Software_Development_on_the_E3xx_USRP_-_Building_RFNoC_UHD_/_GNU_Radio_/_gr-ettus_from_Source

Attachment: fm_example_host.grc
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Attachment: fm_example_usrp.grc
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