I kindof have a similar problem. Guess I havent understood this yet. I want to generate a very basic signal at 10.000000 MHz. A little up or down is not relevant, but I want to hear a signal at all. I have a very sensitive HF receiver right next to my dummy load, so that should work with a very faint rest.
In GRC I have a signal generator and a USRP2 sink. Can you please tell me reference values for * sample rate * interpolation on the usrp2 Is the product of these two required to be 100M? Or 50M? Thanks in advance for the clarification. BR Markus Am Mittwoch, den 03.11.2010, 17:27 -0400 schrieb Dan Harasty: > Marcus wrote: > > It's usual in telecom systems for there to be some kind of AFC on the > > receive side to compensate for transmit-side frequency error. > Can't this problem also be solved with a transmit-side correction? > > If the "error" in this particular USPR2 LO is about 900MHz - > 899.99701MHz = 0.00299 MHz, then won't telling the USPR2 to modulate to > 900.00299 MHz pretty much get the tones to the right place? > > I imagine the correction will change with device temperature and age, > and also by intended "center frequency". > > But as a first cut, won't that work? > > -- Dan Harasty > > > > On 11/3/2010 4:59 PM, Marcus D. Leech wrote: > > On 11/03/2010 04:00 PM, Steve Mcmahon wrote: > >> Hello: > >> > >> I am still somewhat new to GNU Radio. I am running GNU Radio 3.3.0 under > >> openSUSE 11.2, and I have two USRP2 boards, each with a WBX daughterboard. > >> I need some help understanding some fundamental things about GNU Radio and > >> the USRP2 and upconversion. > >> > >> I am trying generate a tone at 900.001 MHz (900,001,000 Hz). I am using > >> GRC to construct a simple flow graph where I have a signal source block > >> generating a 1 khz cosine at a sample rate of 195.312 khz (=100e6/512), > >> connected to a USRP2 sink block with the "decimation" parameter set to > >> 512, and with the "frequency" parameter set to 900M. I then look at the > >> output on a spectrum analyzer. My understanding was that I should see a > >> clear spike at 900.001 MHz, but I don't. Instead I see a peak at 899.99701 > >> MHz. What am I doing wrong? I'm using the internal USRP2 clock. Is this > >> happening because the internal clock is good to only 7ppm? > >> > > There are two sources of error--one, as you've observed is the precision > > of the reference clock on the USRP2. And the other is whatever residual > > measurement error your > > Spectrum Analyser has. Synthesized LOs are only as good as the reference > > clock, at least from > > a frequency-precision perspective. If you want to do better than that, > > then you can use an > > external 10MHz reference clock, such as a GPS frequency standard. > > > > This is entirely normal for synthesized RF gear. Measure just about any > > commercial radio out there with a precision measurement device, and > > there'll be some residual > > frequency error, unless you get lucky. > > > > It's usual in telecom systems for there to be some kind of AFC on the > > receive side to compensate for > > transmit-side frequency error. > >> In general, how do I need to setup the frequency of a USRP2 source if I > >> want to place tones in the spectrum? I thought it was simple upconversion. > >> If I want to modulate a multitone signal (say with sine components 1 KHz, > >> 3 khz, and 7 khz) to obtain an upconverted signal with tones at 901 MHz, > >> 903 MHz, and 907 MHz, then I simply set the "frequency" parameter of the > >> USRP2 sink to 900 MHz, right? How exactly does the USRP2 do the > >> upconversion? What exactly does the "frequency" parameter do? > >> > >> > > The USRP2 takes your quadrature-sampled baseband signal, and > > interpolates it up to the required Tx-side sampling rate. It programs the > > Tx LO on the daughtercard to > > the desired frequency, and sends it on to the Tx mixer. Sometimes, due to > > LO frequency step > > size limitations on specific daughtercards, the USRP2 FPGA will use a DUC > > (Digital Up-converter) > > stage to get to exactly the desired frequency. > > > > I'm not sure whether you meant 901,903 and 907Mhz, or 900.001MHz, > > 900.003Mhz, and 900.007Mhz. > > > > For purposes of experiment, you can have 3 different signal generators, > > add their outputs, and send the resulting multi-tone baseband stream on to > > the USRP2. > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio