Re: [Discuss-gnuradio] Flush samples of blocks when changing centrer frequency

On Thu, Feb 5, 2015 at 11:30 AM, Jorge Gallo <jmiggal@gmail.com> wrote:

Hi,

I have a python flowgraph with several blocks.

One of them is a "filter.single_pole_iir_filter_ff" which does a moving average. The last block is a Sink to file block.

I scan several bands, 10MHz each, in order to get the power of the signals in those bands. I use moving average to get an average of 5 readings in each band.

In order to change the center frequency, I stop the flow-grahp, reconfigure the USRP center freq and then start the flow-graph again.

You can use the message port[1] in uhd source/sink or stream tags [2] to change the center frequency

 

I guess samples from the previous scans remain in internal block buffers since I get power in samples of BAND2 (BAND1+10MHz) which are only present in BAND1. That is, the moving average is effective between bands and I only want to be effective in the same band.

I thought that stop() and start() signals would reset the entire graph but I am afraid it doesn't.

Is there a way to flush those samples so that everytime I run the frequency changed flow-graph I don't get the samples from the previous band?

UHD source will give rx_time, rx_rate and rx_freq tags whenever there is a tune request to a new frequency. You can use these tags to get rid of unwanted samples.

 

Many thanks in advance.

Jorge

 

[1] http://gnuradio.org/doc/doxygen/page_uhd.html
[2] https://github.com/gnuradio/gnuradio/blob/master/gr-uhd/examples/python/freq_hopping.py
 

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Regards
Sreeraj Rajendran
http://radioninja.in/