On Mon, Apr 21, 2008 at 2:21 PM, Wireless Monster <[EMAIL PROTECTED]> wrote:
> After the gmsk modulation (blks2.gmsk_mod) I have to scale the value (for > example by multiplying it by 8000) before sending it to the USRP to get the > resulting signal centered at the right frequency. If don't do it the output > signal is shifted... I assume some minimum signal level is needed in the > FPGA blocks to work correctly. The "full scale" output to the RFX boards is +-32767.0. It is not recommended that you actually use this, as it will drive the RFX output stages into a strongly non-linear operating range, increasing noise and spurious signals significantly. From empirical measurements, the RFX boards can only get to about 15% full scale before they go into gain compression. That would be about +-5000 into usrp.sink_c. It's likely that what you were seeing before was a spur from the local oscillator feedthrough of the mixer, can be up to 4 MHz away from your requested frequency. Once you sent a waveform of significant amplitude out to the card, you then saw it instead of the spur (which was still there, but much lower in power). So it looks like one signal "shifted" somehow, but was really two different signals. -- Johnathan Corgan Corgan Enterprises LLC http://corganenterprises.com/ _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio