On Thu, Mar 17, 2005 at 03:28:26PM -0500, Dinkar Bhat wrote: > Thanks for the info. One of my issues is the detection of the pilot > frequency (which is a specific frequency relative to the > channel). Now, using FFT on the samples that I captured using the > ADC, I geta certain frequency resolution (bin size) that is > inversely proportional to the the length of the ADC.
> But I might miss the pilot and hence I was wondering if I should > sample at much higher rate than 2* max frequency. Even then I might > miss the pilot, and I am wondering what is approach? > > Dinkar > No need to sample at much higher than 2x the bandwidth of interest. The bandwidth of interest is 6 MHz, thus, assuming your IF frequency aliases down to something convenient, you should be able to sample at something on the order of 2.5 * 6 = 15 MS/sec (real). The pilot tone is easy to see, particularly if you use an averaging FFT. See last night's new code ;-) In this screenshot, the pilot is clearly visible at -2.7 MHz: http://comsec.com/images/atsc-ch44.png It's RF channel 44 (653 MHz), KRXI-DT 11.1, the Reno FOX affiliate. I captured this using a 4937 eval board with an IF of 5.75 MHz, connected to a USRP with a "Basic Rx" daughterboard. The antenna was a pair of rabbit ears sitting on my kitchen table. I was running the usrp_fft.py example code. The sample rate across the USB is 8MS/sec, complex. The screen shot is of a 512 point FFT. Eric _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
