Hi, Can some one explain in a little bit detail how this software PLL can be implemented and how this synchronization can be acheived. I am using RFX2400 and facing same problem.
First I tried to solve the problem by calculating the frequency shift at receiver end by using usrp_fft.py and then by adding/subtracting that frequency from RX USRP frequency. But it dont solve the problem. and secondally I am confused why we dont discuss TX clock which is 128MHz (true...?????), I mean what is the role of that. Thanks Johnathan Corgan-2 wrote: > > On Wed, Jul 23, 2008 at 3:57 PM, Chris Stankevitz <[EMAIL PROTECTED]> > wrote: > >>> I am having lots of issues with the USRP 64MHz (20ppm) on board >>> oscillator which does not allow me to get exact and constant RF >>> frequencies >>> out of the RFX900 board. I can not really fix that in SW so I was >>> thinking >>> about replacing the 64MHz crystal with a more precise one. Has anybody a >>> suggestion of which part to use? >> >> I have replaced the crystal with the 20ppm crystal, but I was unable to >> get >> an "exact and constant" frequency. I ultimately added a software PLL to >> track the clock errors. Before I upgraded my software PLL, I used a >> signal >> generator as an external clock source which worked very well. > > Just to reiterate, it's not physically possible to get "exact and > constant" frequencies in a receiver. This is not a bug. All > realistic radio receivers will have to deal with frequency and phase > offsets. Sometimes you can reduce them to the point where you can > ignore them. Other times, such as in mobile wireless or satellite > communications, Doppler effects will make any existing frequency > stability issues worse. > > Decades of research have gone into algorithms one can use on a > receiver to recover the exact carrier phase and frequency of a > received modulated waveform, resulting in many tried and true > engineering solutions. Some these, such as software PLLs as Chris > mentions, are available in GNU Radio for your use. > > I believe (ISTR) that there are 5 PPM versions of the crystal on the > USRP that fit the same solder pattern. But that still leaves you with > many KHz of potential offset and drift at 900 MHz, so unless your > chosen modulation can withstand that, you'll still need to solve the > receiver synchronization problem. > > -- > Johnathan Corgan > Corgan Enterprises LLC > http://corganenterprises.com/ > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > -- View this message in context: http://www.nabble.com/64MHz-USRP-Oscillator-tp18621090p18632191.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
