On Fri, Sep 13, 2013 at 10:53 PM, Brian Padalino <bpadal...@gmail.com> wrote: > On Fri, Sep 13, 2013 at 3:58 PM, Alexandru Csete <oz9...@gmail.com> wrote: >> On Fri, Sep 13, 2013 at 3:53 PM, Brian Padalino <bpadal...@gmail.com> wrote: >>> On Fri, Sep 13, 2013 at 2:19 AM, Ralph A. Schmid, dk5ras >>> <ra...@schmid.xxx> wrote: >>>> Hi, >>>> >>>> I am using bladeRF with gr-osmosdr, gnuradio 3.7 and gqrx, so far a fine >>>> radio. One thing, when using gqrx...I am limited to USB2.0 at the moment, >>>> so >>>> I use a sampling rate of 8 Ms/s, and in this mode I have big problems with >>>> images from the neighbour frequencies that are still within the 26 MHz >>>> bandwidth, or whatever the maximum BW is. >>>> >>>> Is there some command to set this bandwidth to a smaller value? I assume >>>> that this would improve my RX experience a lot :) A quick look at osmocom >>>> showed me nothing, but maybe I missed smth. >>> >>> The gr-osmosdr interface allows for a bandwidth setting to be changed here: >>> >>> >>> http://cgit.osmocom.org/gr-osmosdr/tree/lib/bladerf/bladerf_source_c.cc#n581 >>> >>> The driver will figure out which bandwidth is closest to what you want >>> with a minimum of 1.5MHz and a maximum of 28MHz for the low-pass >>> filters. >>> >>> It will definitely make a world of difference by actually applying the >>> LPF and removing the aliasing. >>> >>> As for official support for gqrx, it's next on our list. We need to >>> get on the gqrx mailing list and figure out what code we need to >>> write. >>> >> >> Actually, it was a deliberate choice not to have explicit support for >> that API call since it seemed unnecessary. Wouldn't one always want to >> use the narrowest analog bandwidth corresponding to a given sample >> rate? If yes, the setting may as well happen as part of the sample >> rate configuration and best handled at a layer that knows about the >> specific device. Am I wrong? > > One may want to listen to an LTE signal that is 5MHz wide, but sample > at the standard 30.72MHz sample rate. In this case, I would think the > LPF might want to be set smaller than 28MHz (maybe 8MHz?) but still > sample at 30.72MHz? > > Maybe another case is wanting to see 5MHz worth of bandwidth, seeing a > weak signal, move the weak signal into the LPF region, and tighten the > filter such that you could increase the gain without clipping the ADC > in case there is a near-by blocker? > > I agree you can shoot yourself in the foot very easily by separating > the two of them and have lots of noise alias in, but keeping them > separate, in my mind, is still a very reasonable thing to do. > > Maybe, for the case of gqrx, an option for gr-osmosdr at device > opening (and passed to the constructor) is to have a bandwidth setting > (auto or manual) that when put into auto mode will do as you suggest, > and set the appropriate low pass filter bandwidth as well as warn if > the sample rate is too low, and there will be aliasing due to the LPF > not being tight enough? > > What are your thoughts?
Hi Brian, I didn't think of these cases - they make sense. I have added an option to set the bandwidth in the I/O configuration dialog. It is available in the git repository. I could test it with hackrf anbd I hope somebody else can test it with the bladerf. Currently it does no checking - just passes the value directly to gr-osmosdr. Alex _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
