On 08/02/2011 08:10 AM, Delgado, Christopher wrote: > Have some questions regarding received signal levels and what seems > like LO leakage on transmit side. We are using N210 with WBX (UHD > driver). This issue seems to be pretty independent of carrier > frequency. > > 1) Receive sensitivity - We're cabling in a CDMA2000 carrier (1.2288 > MHz bandwidth) from a femtocell base station we have. The transmit > power is about -80 dBm. We've done a simple test with GRC to receive > this signal, write to a file and do PN correlations in Matlab to > verify the integrity of the data. With the signal level of -80 dBm > and the rx_gain in the GRC gui set to maximum (38 dBm) the I/Q data > seems to be about 3 bit values (about +/- 4 or 5). These values seem > a bit low for this signal level. On other SDR receivers we use (not > usrp) with max gain, signals over the air from base stations are > about -90-95 dBm and toggle about 6 bits on ADC. In short, I'm > wondering if this is expected behavior or if there is another analog > gain setting to change on receive side.
You didn't state what frequency you are using or what decimation, but the noise figure should be under 6 dB, and that is the only true measure of sensitivity. You can always add more digital gain in the fpga, but I don't think you need that. Are you sure you are using the correct antenna input? Also, the grand-daughterboard is static sensitive. In order to check to see if yours is working, please put a known level sine wave in from a signal generator, and send us a screenshot of the uhd_fft display along with the settings you used. > 2) Transmit leakage We've set up a simple program in GRC to take the > received IQ from the same base station and retransmit them on a > different frequency. The receive is in the 800MHz band, and we've > tried transmit on both 500MHz and 1GHz. Looking at the output on a > spectrum analyzer as well as just plotting IQ in Matlab, there is > some strong carrier leakage, in fact the carrier is dominant over > the signal for all practical ranges of signal level at the input. > With the input at -30 dBm and the rx_gain set to max 38 dBm the > signal begins to finally overtake the carrier however this signal > level is obviously not practical. Furthermore, the gain parameter in > GRC's UHD: USRP Sink block seems to do nothing based on observing > live spectrum of the transmit signal. The DC offset of the receive > data seems to be negligible - we're writing it to a file before it > goes out. Wondering what could be causing such strong LO leakage. I am confused here. Is this carrier leakage out of the transmit port, or leakage of TX into the RX? Matt _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
