Forum: GNU Radio alpha and look ahead value in gr_peak_detector_xb_0

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Markus F. (Guest)
on 2009-05-08 02:27
(Received via mailing list)
Hi All,

i want to build an application including a peak detector, therefore
i am using the <gr_peak_detector_xb_0> which has a TH Factor Rise and
TH Factor Fall to detect a peak. It also has a alpha and a look ahead
value.

As far as i understand, if the Threshold finds a possible peak
it searchs if the peak goes further above. It searchs so many times
as the look ahead value consists. If the look ahead value is 10, then
he looks 10 times further. The search will only be stopped if the
TH Factor Fall occurs or it reach the 10th value. If the TH Factor Rise
occurs it calculates an average value according to the EWMA principle.
Therefore we need alpha. A higher alpha value let the average value
moving faster down and backwards, a lower alpha value --> moving the
average value slower down. Th formula for the alpha i know is
alpha = 2/(N+1)
whereby we know alpha and want to know N, so
N = 2/alpha - 1

So a higher alpha value produces more peaks.

I setted up my <gr_peak_detector_xb_0>, but it seems
not to work correct. it reacts on every signal even
noise.
I changed the TH Factor Rise to 10e15 but he still produces
peaks.

Is this a Bug or what ?
Is my understanding on the Peakdetector correct ?

I added my grc file in the hope somebody can tell me more.

regards Markus
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