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
timestamptester.grc
Description: application/gnuradio-grc
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