[USRP-users] OTW sc8

Josh Blum josh at ettus.com
Wed Sep 5 15:53:02 EDT 2012



On 09/05/2012 12:21 PM, Tim Pitman wrote:
> I'm trying to switch from the default (which is sc16, correct?) to
> using the sc8 OTW format. I changed my stream_args call from:
> 
> uhd::stream_args_t stream_args("fc32");
> 
> to:
> 
> uhd:stream_args_t stream_args("fc32", "sc8");
> 
> It compiles and runs just fine. I observed 1/2 the ethernet throughput
> being used as expected. The waveform also appears unchanged on the
> spectrum analyzer but the SNR and constellation are horrible. Am I
> missing something?
> 

You might want to set the peak parameter to get the best use out of the
more limited dynamic range, see peak:

http://files.ettus.com/uhd_docs/doxygen/html/structuhd_1_1stream__args__t.html#a4463f2eec2cc7ee70f84baacbb26e1ef

"""
peak: specifies a fractional sample level to calculate scaling with the
sc8 wire format. When using sc8 samples over the wire, the device must
scale samples (both on the host and in the device) to satisfy the
dynamic range needs. The peak value specifies a fraction of the maximum
sample level (1.0 = 100%). Set peak to max_sample_level/full_scale_level
to ensure optimum dynamic range.
"""

-josh

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