Hi,
1) Using high accuracy function generator and USRP with Basic-RX, I tried to investigate the dynamic range of this board. The following behaver was obtained (0 dB gain was used in all experiments with decimation of 8): a) With Sinewave signal at frequency =250KHz and 0dBm input power to BasicRX we get , Theoretical calculations : When 0dBm signal injected into 50 Ohm load, then signal RMS = 0.225Volt and Signal voltage P-P = 0.636396103Volt. USRP readings : The maximum counting obtained from USRP for this signal was 4845. b) With Sinewave signal at frequency =250KHz and 5dBm input power to BasicRX we get , Theoretical calculations : When +5dBm signal injected into 50 Ohm load, then signal RMS = 0.4Volt and Signal P-P = 1.13137085Volt. USRP readings : The maximum counting obtained from USRP for this signal was 8337 c) With Sinewave signal at frequency =250KHz and 9dBm input power to BasicRX we get , Theoretical calculations : When +9dBm signal injected into 50 Ohm load, then signal RMS = 0.64Volt and Signal P-P = 1.81019336Volt. USRP readings : The maximum counting obtained from USRP for this signal was 13096 d) With Sinewave signal at frequency =250KHz and 10dBm input power to BasicRX we get , Theoretical calculations : When +10dBm signal injected into 50 Ohm load, then signal RMS = 0.71Volt and Signal P-P = 2.008183259Volt. USRP readings : The maximum counting obtained from USRP for this signal was 13570 (Saturated). Discussion : >From the above results we see that the BASIC-RX is saturated when the input signal power was +10dBm. This is logical, since the maximum input signal to the USRP ADC AD9862 is 2Volt P-P (according to its data sheets). But, what is not logical is the value obtained from USRP FPGA. Since the incoming data is 16bit signed number (for I and Q), we should get +/- 32767 readings for the maximum input signal of 2V P-P. Instead, we have maximum reading of 13570. I don't know how this number was generated, but it should be scaled to make use from the full dynamic range offered by using 16 Bit data transfer. 2) I Think there is a problem in the 8 bit data transfer. As we know, if we have 12 bit number (for example), and we would truncate it to 8 bit number, we should take the most 8 significant bits from it and discards the rest least 4 bits. This is not happening in the 8 bit data transfer. When the input signal is power is low, we get weird waveforms as shown in the following snapshots. http://rapidshare.com/files/78343220/8-bit-samples-scope.tar.gz As shown, unless the input signal power is high (9dBm was the best) we get a very distorted signal when using 8 bit data transfer. Note: I'm using the latest trunk USRP rbf file (the 8 bit samples transferring was restored). 3) FYI, the maximum measured SFDR for Basic-RX was about 55dB (when the input signal was +4dBm and the gain was 0dB which gave this maximum SFDR) 4) FYI, the maximum measured SFDR for DBSRX was about 40dB (when the input signal was -20dBm and the gain was 26 dB which gave this maximum SFDR). I hope we use these experiments to enhance our magnificent USRP. Best Regards, Firas A. -- View this message in context: http://www.nabble.com/USRP-Dynamic-Range-and-8-Bit-Problem-tp14471573p14471573.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
