UHD source + sink PROBLEM

GNU Radio
1

Here is my code for transmitting data from a file:
from gnuradio import gr
from gnuradio import uhd

symbolrate=0.510**5
samplerate=20symbolrate # 1M
fg=gr.top_block()
src=gr.file_source(gr.sizeof_gr_complex1,‘data.txt’,False)
snk=uhd.usrp_sink(‘serial=1R24X9U1’,uhd.io_type.COMPLEX_FLOAT32,1)
snk.set_samp_rate(samplerate)
snk.set_center_freq(2.410**9)
fg.connect(src,snk)
fg.run()

And I run the uhd_fft.py on another USRP… i constantly get a peak at
centr
frequency for data being sent, why?
http://old.nabble.com/file/p33115067/data.txt data.txt

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2

On 01/10/2012 05:48 PM, UB wrote:

snk.set_center_freq(2.4*10**9)
fg.connect(src,snk)
fg.run()

And I run the uhd_fft.py on another USRP… i constantly get a peak at centr
frequency for data being sent, why?
http://old.nabble.com/file/p33115067/data.txt data.txt
Many different debugging approaches:

a) Plot your data with an FFT sink–rather than a usrp_sink. Is there a
spectral peak at DC?

b) There will always be a small amount of DC offset in both directions
(RX and TX) that will
cause an anomaly around DC. You can null this out to a certain
extent using the calibrate
routines (assuming you have a USRP2/N2XX and either a WBX or SBX
card).

c) You can always offset tune your TX, to take the DC offset anomaly
away from your main
transmit bandwidth. Similarly in RX.

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

3

To expand on what Marcus said about DC, look advanced tuning with
tune_request_t:

http://files.ettus.com/uhd_docs/manual/html/general.html#two-stage-tuning-process

Cheers,
Ben