On Thu, Feb 4, 2010 at 4:37 PM, Mir M. Ali <[email protected]> wrote: > In GRC I have a complex sine source with amplitude 10 and frequency 2000Hz > sampled at 4000Hz as a input to the costas loop through a throttle block. > The max and min frequency used is +/- 0.157rad/sample which is 100Hz > /sample. When I see the output on scope and FFT scope i see peak at 0Hz in > the FFt scope but on the oscilloscope I see a sine wave with amplitude 10 on > the Inphase component and 0 in the Q component. Why? > The output is shown in the figure. > http://img690.imageshack.us/img690/7879/snapshot1u.jpg > Thanks
I assume you are using a bpsk costas loop (m=2). In bpsk all of the data is in the real portion of the signal, therefore any amplitude in the Q is considered error. In order to recover the data, the loop rotates the data so the Q component to 0, and the I component is presumably +/-1. If you were to do the same with a qpsk loop (m=4), you should see both components looking like a saw wave. Additionally, a standard costas loop assumes that the data has already been sampled. Your samples per 'symbol' is higher than 1 in this case, and the loop output would not be predicable if you were sending data. Jason _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
