Re: Strategies to save/display low sample-rate data

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On 10/04/2024 19:44, John Ackermann N8UR wrote:
> On 4/10/24 11:29, Fons Adriaensen wrote:
>
>> Both the decimation and 80 size 1024 FFTs per second should be peanuts
>> for any modern PC...
>>
>> And of course you don't need to do the FFT again for every sample,
>> it just generates a lot of redundant data.
>
> I understood that if you have a 1024 bin waterfall, it takes that many
> samples to fill it and output a vector.  With a sample rate of 80, that
> means about 12.8 seconds to show one line of the waterfall.  Or do I
> have that wrong?
>
> (I used 80 samples/sec for simplicity.  The actual rate after decimating
> from a 1.536 ms/s stream is 93.75.)

Hi John,

Yes, that is correct. Ultimately you're hitting the uncertainty
principle for the Fourier transform. A 1024-point FFT at 80 samples/s
has a frequency resolution of 78 mHz. You need to process at least 1 /
78 mHz = 12.8 seconds of signal to achieve that resolution.

Best,
Daniel.