[USRP-users] problem with loopbacks when using USRP

Marcus Müller marcus.mueller at ettus.com
Tue Jul 28 11:53:32 EDT 2015


Hi Jason,
> see a ton of U's and the occasional D's in the console.  But in reading,
> it looks like the U's are OK to ignore.
Nope. U means you're simply not sending getting data for a whole 
UHD/CHDR packet worth of samples. Which basically means: unpredictable 
stuff happening to your signal.
D is a sequence error. You're pushing your PC or your network interface 
too hard.

Is this happening in a VM? If that's the case, you will either need to 
experiment with the different kind of virtualized Network adapters, 
PCIe-Forward a dedicated one to your VM, in any case set the networking 
mode from NAT to bridged, or (and I think that's most probable) get rid 
of the VM and do this natively.

Greetings,
Marcus
On 28.07.2015 17:47, Jason Matusiak via USRP-users wrote:
>> How are you looping them back?  With a lot of attenuation in the cable, I hope?
> Sorry, that would have been useful for me to mention.... I am going over
> the air via an antenna.
>
>> Also, it's useful when debugging this sort of thing to make your initial RX just an FFT display--does the spectrum look correct?
> It looks pretty flat across the spectrum in this WiFi example.  I also
> see a ton of U's and the occasional D's in the console.  But in reading,
> it looks like the U's are OK to ignore.
>
> I know when I did the OFDM loopback it looked like the attached.
>
>
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> USRP-users at lists.ettus.com
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