Re: How can I split a periodic signal?

[James Wanga]

I'll give this a try and report back. I was also thinking of inducing a large burst on the transmit graph and listening in with a burst tagger on the receive side.

James Wanga

On Thu, Aug 25, 2022 at 1:34 PM Brian Padalino <bpadalino@gmail.com> wrote:

On Thu, Aug 25, 2022 at 4:19 PM James Wanga <jwanga@gmail.com> wrote:

Thanks Brian! 

This is a clever solution. My signal is bursty even through the duration of the pulse. Is the purpose of the second threshold circuit meant to mitigate that by averaging over time?

Yes, the second signal will rise slowly, and decay slowly (think like RC time constant) so if multiple back-to-back bursts come in, or there is a slight fade in the signal, the same burst is kept.  It should also give you a little extra "tail" so that you aren't cutting things off immediately.

Also note the delay in the beginning that tries to center up the energy a little bit so you see some beginning noise levels.

In the end, I get files that should look like what you have, though I did have to play with gains and threshold levels to make it reliable.

Let me know if you have success with this.

Thanks,

Brian

 

On Thu, Aug 25, 2022 at 11:34 AM Brian Padalino <bpadalino@gmail.com> wrote:

On Thu, Aug 25, 2022 at 1:55 PM James Wanga <jwanga@gmail.com> wrote:

I'm receiving a phase modulated signal representing a periodic pulsed byte that looks something like this:

-------------|-|||--||-------------|||--||||-------------|--||||-|-------------

I'm trying to understand how I might split this signal roughly halfway between each pulse of activity so I can save each pulse as a separate IQ fil, bit like this:

------|-|||--||------

-------|||--||||-------

------|--||||-|------

The split does not have to be precise, it only needs to avoid bisecting any of the pulses. Here are some things I've tried.- Creating a custom block on the receiver that uses a timing interval. Unfortunately, the pulses aren't perfectly periodic so eventually this causes the split to drift.

- Since I also control the transmitter, I tried sending an async pmt message from the transmitter to the receiver, but again, since the message is async the timing is too unpredictable to make an accurate enough cut.

- I was also wondering if there is any way to propagate a tag from a transmitter to a receiver if both are in the same flow graph, but I couldn't find any info on how to do this.

Any Ideas? Thanks!

I was looking at a bursty signal in the ISM band that I wanted to save and came up with the attached flowgraph.  The key is the "Burst Tagger" block and the creation of the trigger utilizing the magnitude of the incoming signal.  I utilize two "Threshold" blocks - one on the magnitude itself which should rise pretty quickly, and one based on a filtered version of the magnitude which falls slower.  Both of those are OR'd together to create the trigger and saved with the "Tagged File Sink".

GRC and PDF screen capture both attached.

Hope this helps.

Brian

 

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James Wanga