UHD source + sink PROBLEM

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

symbolrate=0.510**5
samplerate=20
symbolrate # 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(2.4
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

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Sent from the GnuRadio mailing list archive at Nabble.com.

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
http://www.sbrac.org

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

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