[USRP-users] Removing DC offset on USRP B200

Marcus Müller marcus.mueller at ettus.com
Tue Oct 17 17:54:51 EDT 2017


Hi Oliver,

even just considering the time it takes to synthesize a single image for
the B200's FPGA, not counting time needed to learn where to put your
Verilog: Avoid doing things in the FPGA as far as possible. The 20
minutes it costs to go through the first two or three chapters of the
GNU Radio Guided Tutorials[1] will pay for themselves before your
computer can even say "place&route". Obviously, you've already figured
out where to integrate your DDS, but I'd still maintain that at such
modest rates as 5 or 10MS/s, there's no reason to have a fixed purpose
implementation in the FPGA when you could just as well do it flexibly in
software on the host. That's my "here's two tones at 2.4 GHz" example.
It took me about as long to crop the image to this size as it took me to
design this transmitter in the GNU Radio companion. Could have just as
well written it in Python or C++ in nearly the same time :)

Two tones generated in software


Anyway, I'm absolutely still not convinced you can get rid of the DC
offset you're seeing with DSP at all – are you sure it's in the signal
you're sending to the AD936x, or is it maybe more of an analog artifact?

Best regards,

Marcus

[1] http://tutorials.gnuradio.org


On 17.10.2017 03:06, Oliver Wayne wrote:
> How would I then include negative numbers on the Verilog side to kill
> the offset? I'm a bit more comfortable with fpga design than with SDR,
> so for testing purposes I'd prefer to do it that way.

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