Re: Sine wave of only 3 cycles

Dear Sirs,

Thank you very much.
The “head” block solve my problem precisely.

Note:
The flow graph consists of some other blocks at the middle.

Regards,
activecat.

Dear Sirs,

But, another problem arisen.
There is a WX GUI Scope Sink in the middle of the flow-graph to plot the
instantaneous reading.
When the data stream stop by the Head Block, says, at time=t1, the WX
GUI
Scope Sink starts to show zero reading.

The question is, how to see the plot between time=0 and time=t1 ?
The workaround is to save the data into a file, then plot it using
external
tool. This is “off-line” approach.
Is there any “online” approach that doesn’t require any external
plotting
tool, to view the GUI plot between time=0 and time=t1, after the Head
Block
terminates the data stream?

Regards,
activecat

On Thu, Jan 30, 2014 at 10:22 PM, Activecat [email protected] wrote:

tool. This is “off-line” approach.
Is there any “online” approach that doesn’t require any external plotting
tool, to view the GUI plot between time=0 and time=t1, after the Head Block
terminates the data stream?

Regards,
activecat

You can try to use the QTGUI tools instead of the WX ones. When the
data stops, the QTGUI sinks should not update, so it will show you the
last plotted samples. But be aware that it’s a “sampling” approach to
plotting. Basically, it waits for enough samples to plot one full
graph (1024 by default), so it needs to see this amount before it’ll
update.

However, since you’re stopping the flowgraph, don’t be afraid of the
off-line approach. That might be the best way to go. The on-line
approach is designed for streaming data, so what you’re asking to do
is a bit of a different situation that we’d normally work with.

Also, note that we ship a handful of off-line plotting tools with GNU
Radio. There’s a set called “gr_plot_" that use scipy and Matplotlib
to plot the graphs. I made some newer ones called "gr_
plot*” that
uses QT. There not full-featured and may be a bit buggy, but the idea
with these is to have a common feel and UI between using the QTGUI
sinks inside a flowgraph and these off-line plotting tools.

Tom

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