On 01/15/2015 12:55 PM, Anderson,
Douglas J. wrote:
I don't think it's tuning effects, if
I'm understanding that correctly. You mean that after you retune
the USRP, the LO will take some time to settle?
In the script I posted, that shouldn't be a factor, as the
UHD instance is created and tuned when I import the file in
the python interpreter, and the acquisitions are then run
later and without retuning the USRP.
I might be misunderstanding the issue, like if there is
something that needs to settle each and every time an
acquisition is requested independent of actual frequency
tuning.
... but that's the reason for my question: so that I can
better understand the underlying process. Thank you for the
details!
In that case, you're probably just looking at DSP artifacts. The
DSP chain doesn't, as far as I know, run, doing its thing, between
finite_acquistion()
calls. So, it will be in whatever state it was last in, then you
bring it up again, grab some samples, and stop it again. So it
doesn't really have much
of a chance to achieve steady-state operation with the CIC
decimators and half-band filters. At least, that's *my*
understanding of what
finite_acquisition() does.
It may be better for you to set-up a streamer to stream
continuously, and then just discard the stuff you don't want from
the stream. Both the
hardware, and Gnu Radio are really optimized for the steady-state
streaming case.
From: Nick
Foster [address@hidden]
Sent: Thursday, January 15, 2015 10:49 AM
To: Anderson, Douglas J.
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] voltage pulse
from UHD driver
Nothing. The timing might be a little
different -- if it's tuning effects you're seeing,
there's effectively a race condition between tuning and
sample collection. Gnuradio will never discard samples
off the front unless you use a Skip Head block, which
you should probably be doing as evidently you aren't
expecting your samples to be tightly synchronized to any
particular point in time.
--n
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