On 08/10/2019 11:43 PM, Ellie White wrote:
Hi Marcus,
Thanks for the advice. So, I just tried an experiment to test out your
suggestion, and came up with a puzzling result. I set the sample rate
to 4 MHz, and the decimation in the integrate block to 4 MHz, and
recorded data for about 5 seconds. Instead of getting about 5 samples
out, I tried to read the file and was told that there were "no
samples" in the file. I then tried setting the decimation to samp_rate
/ fft_size, and the result there was the same. Any thoughts on why
this might be?
Thanks,
Ellie
Probably buffering in Gnu Radio. How did you terminate the sampling?
If you just interrupted it, there would have been samples "in flight"
that never made it "home".
On Sat, Aug 10, 2019 at 11:17 PM Marcus D. Leech
<patchvonbr...@gmail.com <mailto:patchvonbr...@gmail.com>> wrote:
On 08/10/2019 10:48 PM, Ellie White wrote:
Hi Marcus,
Thanks for your reply. I am not sure how the integration works,
but if you know how the Integrate block does the integration,
then that is how my flowgraph does it. I suspect it is "sum
/reduce /dump" as you mentioned, though perhaps we would need to
investigate the Integrate block's source code to be sure? Thanks
in advance for any additional suggestions you might have on this!
Cheers,
Ellie
Here's the documentation on the integrate block:
https://wiki.gnuradio.org/index.php/Integrate
So, if your samples are coming in at 1kHz, and you want 1 second
of integration time (and an output rate of 1Hz), you'd set the
"decimation" parameter to 1000.
This is one of the reasons I prefer single-pole-IIR filters--since
I can do sample-rate reduction as a separate process, via
keep-one-in-N.
On Sat, Aug 10, 2019 at 7:37 PM Marcus D. Leech
<patchvonbr...@gmail.com <mailto:patchvonbr...@gmail.com>> wrote:
On 08/10/2019 03:40 PM, Ellie White wrote:
> Hi all,
>
> I hope you're doing well! Thanks again for your help with
my questions
> earlier this summer. I've got another thing to ask now; I
am in the
> process of configuring a system to record integrated
spectra using the
> attached flowgraph, and I am trying to determine how to
integrate for,
> say, 60 seconds -- if I want to do this, what should my
decimation be,
> and how do I calculate that? I have been able to
approximate this by
> trial and error, but I would like to know the calculation
behind it.
>
> Thanks in advance for any advice you can provide, much
appreciated.
> Have a good afternoon!
>
> Cheers,
> Ellie
>
It kind of depends on how you're doing integration.
An approach that strictly does sum/reduce/dump then you need
as many
samples as would occur over your desired integration time.
For a single pole IIR filter, it's a bit trickier, and you'd
set the
"Alpha" parameter to:
e^sqrt(sample-rate*integraton-time)
Which will approximate an R-C integrator with the given
integration time.
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