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# [Linrad] Sampling and FFT SDR-IQ

• Subject: [Linrad] Sampling and FFT SDR-IQ
• From: "Thomas D. Dean" <speakeasy.org; tomdean@xxxxxxxxxxxxxxxx>
• Date: Fri, 05 Jun 2009 10:00:28 -0700

```Hi Leif,

I am still working with linrad and the SDR-IQ and trying to understand
things.  Is this is off topic?

In an earlier email, you wrote:

> Now, if you want 4000 to 21000 Hz on a screen that is e.g. 1100 pixels
> wide you would want a bin separation of (21000-4000)/1100 = 15.4545
> Hz/pixel. Linrad can only compute FFT in sizes that are powers of two
> so you would have to use an FFT size of 2048 or more. You may choose
> larger if you like. The sampling rate that you would have to set
> would be:
>  FFT size     Sampling rate
>   2048            31.65 kHz
>   4096            63.30 kHz
>   8192           126.60 kHz
> I would suggest a sampling speed of about 126 kHz

How do I get from (21000-4000)/1100 = 15.4545 to a sampling rate of 2048
or greater.  Is this because in the SDR produces I and Q and I need 2
bins per pixel?

Tom

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LINRADDARNIL