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Re: [Discuss-gnuradio] Spurious Signals and DC Offset
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] Spurious Signals and DC Offset |
Date: |
Thu, 08 Dec 2005 23:25:26 -0800 |
User-agent: |
Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929) |
> 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