On Sun, Mar 17, 2019 at 8:10 AM John Ackermann N8UR <[email protected]> wrote:
> Is there a probe or other function that can capture and hold the maximum
> instantaneous value of a complex stream? If not, is there a way to
> create that capability out of other blocks?
>
One of the AGC blocks that has separate attack and decay rates (agc2_cc or
agc3_cc) could be used to do this: set attack to 1, decay to 0, ignore the
output, and read (1.0 / agc.gain()) to find the peak-hold magnitude.
In my own application, I am using this chain for peak detection *without*
hold:
blocks.complex_to_mag_squared(),
blocks.stream_to_vector(itemsize=gr.sizeof_float,
nitems_per_block=window),
blocks.max_ff(window),
blocks.probe_signal_f()
but you would need to separately poll (at the sample rate divided by the
window length) and max-hold this to catch long-term peaks. On the upside,
as I just found out, it uses less CPU time than running the AGC (on my
processor).
That's what I'm currently doing -- actually, I do a constant mult of
> from 100 to 500 on the source signal (a file of 16 bit IQ recorded from
> an HF SDR).
If the only thing that affects the peak/gain is the recording, perhaps you
could measure the peak in the file offline (that is, separately from
running your real-time flowgraph) and use that to set the gain, instead of
having to interactively monitor anything.
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