Thank you very much. :) On Thu, Feb 4, 2010 at 8:26 PM, Jason Uher <[email protected]> wrote:
> 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 >
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