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On 12/29/2015 03:29 PM, Simon Olvhammar
wrote:
Ok, thanks.
So it removes fft frames at the output, then frames are lost?
What am I missing?
A more concrete question, does e.g. a 10 min measurement contain
the same fft data with no respectively with decimation?
Could you explain more in detail how input/output fft
frame flow look like, with say decimation at 100?
Input time-domain data are presented to the FFT in FFT-size chunks,
the FFT output is integrated with a single-pole-IIR filter, and then
decimated according to decimation. So if you have 1000 integrated
FFT outputs, and decimation is set to 100, you only see 10 of
them, but those 10 are post-integrator.
Let's say your input rate is 1.0e6, and your FFT size is 1000. That
means a new FFT every 1msec. If that is then decimated after
integration with a decimation rate of 100, then you get one
integrated FFT output every 100msec.
Den 29 dec 2015 19:31 skrev "Marcus D.
Leech" < address@hidden>:
On
12/29/2015 01:01 PM, Simon Olvhammar wrote:
Hi,
I have a question regarding the block RA:FFT in the RA
Blocks package.
If I set, for example, the decimation at 100 does this mean
that only 1 in 100 items will be kept?
In that case it would occur to me if, I do say a measurement
of 100 minutes at a signal, I only get 1 minute of data?
Best regards
Simon
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No, the decimation is applied to FFT *output* frames, after
integration. It is typically the case that in radio
astronomy spectrometry
that you integrate spectra over some time period, since the
SNR is typically quite poor.
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