Thank you all! I've fixed this problem. On Wed, Aug 12, 2009 at 12:13 AM, Jeff Brower <[email protected]>wrote:
> Milo- > > > I found sine waves will be terribly distorted when they are generated at > > relatively high frequency(above 5khz) from signal source in GRC. I set > the > > sampl_rate of scope sink to 2Ghz(high enough, I think), and there are > always > > spikes on generated sine wave. This problem is especially distinct when > > generated sine wave reaches 20Khz and the waveform displayed on scope > sink > > is almost "saw wave". There will be nothing to dispaly if I keep on > > increasing frequency to 1Mhz. Is there anybody who met this problem > before? > > or it might only be the display problem in GRC? I guess it might be the > > problem of scope sink which could not achieve that high sweep (sampling) > > rate even I set it correctly. > > > > Attached are snapshot of generated sine waves at different frequencies: > > Your plots are probably fine, depending on what is your sampling rate (Fs). > Think of it this way: if you display a > sine wave near Fs/2 then you only have 2 samples for each sine wave period > (1 per peak) and connecting those dots with > straight lines on a scope graph will look like "spikes", to use your > terminology. > > In the case of your 20 kHz plot, it looks to me like you might have 3 or 4 > or so samples per sine wave period, so my > guess is your Fs is somewhere between 60 and 80 kHz. > > -Jeff > >
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