Re: [Discuss-gnuradio] USRP transient peak from lock, unlock, set decim/freq

[Nick Foster]

On Tue, 2011-07-12 at 11:07 +0200, Johannes Schmitz wrote:
> I am getting some kind of very strong transient peak when using lock
> unlock and changing usrp decimation rate and frequency and in the
> beginning.
> Is this a normal behaviour?
> So each time I reconfigure my system I have to throw away some samples
> to avoid this peak or am I doing something wrong?

This is normal behavior. Each time the daughterboard is re-tuned, there
is a transient as the VCO settles. A smaller (and much shorter)
transient is expected during rate changes as well due to different
filters being switched in and out. It's best to throw away the first few
samples after changing frequency or rate.

--n

> 
> I made this short example program and the peak can be found at the
> beginning of the logged data and somewhere in the middle. The
> beginning peak only occurs sometimes. So make sure to run it several
> times if you want to see it.
> It happens in USRP1 as well as USRP2.
> 
> I hope somebody can confirm this or tell me that the problem has been
> removed in newer gnuradio versions.
> 
> Johannes
> 
> #!/usr/bin/env python
> 
> from gnuradio import gr
> from gnuradio import usrp
> from gnuradio import usrp2
> from gr_tools import log_to_file
> 
> from time import sleep
> 
> class top_block(gr.top_block):
>     def __init__(self):
>         gr.top_block.__init__(self, "fusb error")
> 
>         self.u = usrp.source_c ()
> #        self.u = usrp2.source_32fc('eth1')
> 
>         self.sink = gr.null_sink(gr.sizeof_gr_complex)
>         self.connect(self.u, self.sink)
> 
>         log_to_file(self, self.u, "data/test_u.compl")
> 
>     def reconfigure(self):
>         self.lock()
>         sleep(1)
>         print 'lock'
>         self.unlock()
>         print 'unlock'
> 
> if __name__ == '__main__':
>     app = top_block()
>     app.start()
>     sleep(1)
>     print 'start'
>     app.reconfigure()
>     print "reconfigured"
>     sleep(1)
>     print 'now stopping'
>     app.stop()
>     print 'stopped'
> 
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