We are using the RFX-400 board (without housing) with an appropriate aerial connected to TX/RX.
I'll assume appropriate means a 1/4 lambda vertical without a real ground plain. Still, that's ok. Using various examples (usrp_fft.py, usrp_wfm_rcv.py and usrp_nbfm_rcv.py) we attempted to receive a signal over-air, generated by a handhold portable radio unit. Unfortunately We were unable to receive our signal. I did this using usrp_nbfm_rcv.py and a NBFM signal from an amateur 440 MHz transceiver, with a loaded 1/4 wave (stock antenna from a Yaesu VX-1R, to be precise) as the receive antenna. With 0.5W into a similar antenna a few feet away, I got a full quieting signal. I was able to copy signals from a repeater that was ~10km away. The quieting was noticeably worse than with a conventional receiver (Yaesu FT-709R, made ~1986, specified receive sensitivity roughly 0.21 uV for NBFM, 10 dB SINAD postdetection). This is about -120 dBm. We then connected a signal generator directly to TX/RX and experimentally determined that the RFX-400 has an RF sensitivity of approximatively -105 dBm. Without specifying the receive modulation and especially the detection bandwidth, this is not very meaningful. NBFM demodulation for 10 dB SINAD is quite different from MDS (minimum discernable isgnal) at 500 Hz bandwidth for CW. I'll assume you mean the level that caused perceived quieting for NBFM. Is this consistent with other peoples findings? That matches my subjective impression pretty well. I would have guessed -110 dBm for NBFM at minimum workable SNR, but I didn't fire up my HP 608E, which takes an hour to warm up and stabilize. I should do this some time; there's humor in using such a device to characterize a software radio. Is it possible that the high speed digital signaling on the USRP motherboard is significantly reducing the sensitivity of the daughter-board? Yes, it is possible. You should examine the circuit diagram and determine what kind of noise floor you would expect, given the NF of the first RF amplifier and losses before it; your experiment is not enough evidence to conclude that there's any such interference. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
