Re: [Discuss-gnuradio] Spurious Signals and DC Offset

[Matt Ettus]

>   1) noise_ave_pwr.jpg
>     * normalized average power over time
>     * is there any reason why the power would start high then go low?

The first samples could be corrupted because the pipeline may not be
cleared.  Drop the first samples

>   2) noise_ave_psd.jpg
>     * average PSD of a chunk of the data
>     * why the very large energy at DC?

It's less than 10 dB above the noise floor.  Turn up the gain and you
won't see it.

>     * why the spikes at +/- 1 MHz and -2 MHz?

You are seeing synthesizer spurs or harmonics of the reference.  You'll
notice that they are only about 3 dB above the noise floor.

>   1) wifi_psd.jpg
>     * fft of 0.5 sec. of data
>     * very pronounced DC component

How many bins in the data?

>    
>   2) wifi_psd_ave.jpg
>     * average PSD of entire data collection
>     * DC component not as pronounced
>     * I guess the half-band filter in the FPGA is causing attenuation at
> the edges of the band?
> 
> I have attached the script I am using to collect the data. It is just a
> customized version of usrp_rx_file.py.  I seem to see these affects
> regardless of frequency, pga gain, or whether I write complex or short
> samples to file.  On a related note, besides space considerations, are
> complex or short samples preferable one to another?

What command line options are you using for the script?

Matt