On Wed, Jul 8, 2009 at 11:54 AM, John DuBois<[email protected]> wrote: > I am puzzled by a very basic issue relating to the usrp1 output. Using GRC, > I connect the usrp output through a complex to mag conversion to a scope > sink and tune to, say, 1GHz. The daughter board is a DBS_RX. > > Using a cw signal generator, I tune for a maximum usrp output and then raise > the usrp input up to about -45 dBm. As the input increases, I see rising > output values (on the scope display) from just above zero to a maximum of > about 16400. > > The puzzle is this: if the usrp A/D converter is 12 bits for I and Q > channels and I am doing a complex to magnitude conversion, why don't I see > 4095*1.414 as the maximum output number? > > The maximum output I do see seems like 14 bits, but without any 1.414 > factor. > > What am I missing ??
Decimation and Interpolation using CIC filters causes bit-growth which is only marginally compensated for using bit-shifts. Moreover, CORDIC mixing causes bit-growth in the output vector as well. Hopefully exploring those avenues solves your puzzle. Good luck. Brian _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
