After some further investiagation, it appears that this may be a slow, long term analog drift in the cosine wave source (perhaps due to single precision math?). The voltage values aren't the same at each point in the waveform - they slowly drift over many minutes of computer runtime.
-- Tom, N5EG On Fri, Dec 4, 2015 at 3:48 PM, Tom McDermott <[email protected]> wrote: > In working on some waveform sampling tests, have encountered an apparent > drift > between two gnuradio sources that are run at the same rate. I've tried to > structure > the flowgraph so that the QT GUI does not get involved in the exact sample > count > integrity between two flow graph paths. > > The attached flowgraph constructs a sampling pulse near the zero-crossing > time of > the cosine wave, then displays that sampled analog value. Over time, the > cosine > source appears to be slipping in time compared to the square wave source. > The > analog sampling pulse samples the cosine source 'near' the zero crossing. > But with > increasing run-time of the flow graph, it appears to be drifting off. I'm > at a loss to > explain this. > > Attached is the simplest GRC flowgraph that demonstrates the effect. It > needs to > run for a few tens of seconds before the analog sampled value starts to > grow. > The time sample at 6 milliseconds is the sampled analog value. Even if > it's not exactly > zero, it should remain relative stable in analog value. > > Any advice on what I might be doing wrong here? > > -- Tom, N5EG > > > > > > >
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