[hpsdr] Mercury Rx on 144 MHz

[Phil Harman]

> Hi Phil, Maximo,what about the Nyquist criterion and aliasing?? Input
> frequency < 122,8MHz/2  !73, Hans, DL2MDQ.
>
>
> -----Original Message-----
> Date: Sun, 01 Aug 2010 14:17:59 +0200
> Subject: Re: [hpsdr] Mercury Rx on 144 MHz
> From: "Phil Harman"
> To: "Maximo EA1DDO_HK1DX" ,
>
> ***** High Performance Software Defined Radio Discussion List *****
>
>
>

Hi Hans,

The Nyquist criteria is often miss understood.  What Nyquist states is that
that you need to sample a signal at least twice the 'information rate' not
twice the carrier rate.  So if you wanted to recover the 144MHz carrier
then you would need to sample at least twice this frequency.

Since we are only interested in the modulation we can sample at a much
lower rate.  For reception on 144MHz we make use of the alias responses
that result from sampling signals.

So a signal at 144MHz will alias to  144 - 2*(122.88/2) = 21.12MHz.


73's Phil...VK6APH


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