Re: Waterfall Rate and FFT2 Size

[VK2KU <clearmail.com.au; vk2ku@xxxxxxxxxxxxxxxx>]

Hi Leif,

> > With the waterfall averages set to 50, that makes 7.4s per
> > waterfall line, which is about what I observe. FFT2 resolution
> > bandwidth would be 111111/16384, or 6.78Hz without windowing, and
> > 10.17Hz with a sin^1 window, which is what Linrad reports.
>
> The transforms overlap at the -3 dB point of the window. You should
> get 7.4 s per waterfall line without a window, but with a window the
> time becomes shorter:

Ok, I understand.
You are right about the time, I must have used an old note I made,
and then changed some parameter!


> Win   time factor
>  0       1.0
>  1       0.666
>  2       0.5
>  3       0.416
>  4       0.364
>
Right, I had figured out the factors, which are mostly obvious anyway
(except the last 2).
Should that be -6dB for the overlap point?
From the numbers we are obviously talking about the half height,
and this is a voltage scale, isn't it?

>
> For fft1 it is a good idea to set a high bandwidth like 200
> Hz with a sine 3 window. It gives a rather wide peak but with
> very good shape factor. It will filter out even very strong
> signals adequately (which a sine window would not do)
>
OK, done that. Actual bandwidth comes out at 130Hz.

Guy

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