Thanks very much Martin!
**Amplitude Parameter Ah. ok! I guess i'll have to look into the variation, I assume it would be the same for multiple copies of the same USRP model. **Freq Mod I'm using GNU Radio 3.6.0, I dont think there is a NCO block.. has this been surpassed by the functionality of another block? **Real Time Scheduling I'll check to see what my error was tomorrow... It might be a while before I get some results but i'll be sure to post what I get! -Michael On Tue, Jun 26, 2012 at 6:30 PM, Martin Braun (CEL) <[email protected]>wrote: > On Mon, Jun 25, 2012 at 09:29:01PM +0930, Michael Hill wrote: > > **Amplitude Parameter > > > > The Amplitude parameter affects the Amplitude dB output, but from what > i've > > determined / read, it is only linear up to a certain level. > > > > E.g. I thought I read somewhere that 1 should be considered the maximum > digital > > amplitude but (for example) that for the RFX1200 the maximum should be > > considered to be 0.2 before the dB amplitude increase as a factor of the > > amplitude parameter starts to be come non-linear. Is this due to the > fact that > > the maximum power output is stated as being 200mW? E.g. Can I therefore > > correctly assume that for the XCVR2450 that 0.1 should be the maximum > value for > > the linear region? > > No, you can't. All of this is rule-of-thumb, trial-and-error and > experience. Some call it black magic. > In theory, amplitude==1 would saturate you ADC (much earlier than the > d'board), and such a signal would radiate (using the d'board) at > approx. 200mW. > > > Also is the amplitude (db) fft plot the idealised / theoretical power I > assume? > > It is not theoretical, but it is not calibrated to physical values. > See the FAQ: > > http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#How-do-I-know-the-exact-voltagepower-of-my-received-input-signal > > > Over what time frame will this change take place? I'm aiming to create > chrips > > using existing blocks. I've read that feeding a saw tooth into a Freq > Mod block > > is the best option.. but i'd like to be able to control the time > > and compression factor.. i guess the time is affected by the period time > for my > > ramp, and amplitude is my sensitivity but again.. what does this equate > to? :/ > > I'm just not sure. > > Hm, are you sure about this? Wouldn't an NCO do what you want? > > > **Bandwidth > > > > The XCVR2450 has a bandwidth of 33MHz according to the first link below, > but > > according to the second.. it says it can cover > > > > Tx: 24, 36, 48 MHz; Rx 15, 19, 28, 36 MHz. I'm a bit confused by this > > You should read the datasheets. The IC powering the XCVR2450 has > switchable filters, and you can set them to any of the bandwidths > mentioned above. If using GRC, see the 'bandwidth' field in the UHD > sink. > > > **Sampling Rates > > > > When running some grc files via gnuradio companion with my USRP N210 > (with a > > Basic Tx Daughterboard), > > > > I often find that I get an output saying something to the effect of > > > > Target Sampling Rate = 22Msps > > > > Actual Sampling Rate = 20Msps. > > > > In fact when testing through a bunch of sampling rates I find it almost > > selecting sampling to rates such as 20Msps, to 25Msps or sometimes > 33.333Msps. > > > > What impacts the selected sampling rate? E.g. is this a factor of the > clocking > > frequency of my computer, the USRP, both or something else? > > USRPs don't run at any sampling rate; they have to be integer fractions > of their clock rate. So if you need 22 Msps, you have to resample on the > host (say, to 25 Msps) and then use that on the USRP. Make sure to > correct for resampling filter delay in your radar measurements. > > > **Real time Scheduling > > > > I still can't seem to get Real Time Scheduling going despite having > added the > > > > @usrp - rtprio 50 > > > > to /etc/security/limits.conf (and also setting Real Time Scheduling to > "on" in > > my top block) > > > > My computer is a 3GHz Quad Core, so i'm surprised I can't this isn't > working > > > > Would chaning it to @usrp - rtprio 99 make a difference? > > Do you actually get an error message stating that RT doesn't work? > > On a side note, I've done OFDM radar measurements using the > N210/XCVR2450 combo and it worked fine. I'd be interested to hear about > your results. > > MB > > -- > Karlsruhe Institute of Technology (KIT) > Communications Engineering Lab (CEL) > > Dipl.-Ing. Martin Braun > Research Associate > > Kaiserstraße 12 > Building 05.01 > 76131 Karlsruhe > > Phone: +49 721 608-43790 > Fax: +49 721 608-46071 > www.cel.kit.edu > > KIT -- University of the State of Baden-Württemberg and > National Laboratory of the Helmholtz Association > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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