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Re: aliasing with X310 BasicRX (higher order Nyquist zone) ?

From: address@hidden
Subject: Re: aliasing with X310 BasicRX (higher order Nyquist zone) ?
Date: Mon, 20 Jul 2020 16:06:09 +0000

Thank you for pointing out the inconsistency of my analysis: the considered 
zone is during sampling, and not during decimation. Setting LO to 56.95 MHz 
perfectly, thank you.


JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe,
25000 Besancon, France

July 20, 2020 5:43 PM, "Brian Padalino" <bpadalino@gmail.com> wrote:

> On Mon, Jul 20, 2020 at 11:32 AM jean-michel.friedt@femto-st.fr 
> <jean-michel.friedt@femto-st.fr>
> wrote:
>> Indeed second Nyquist zone before decimation.
>> My thought was
>> 143.05 MHz -> transpose by 100 MHz using the DDC (NCO at 100 MHz considering 
>> the
>> 200 MHz sampling rate) to reach 43.05, and after transposition, decimating 
>> to reach
>> 8 MS/s (I do have Epcos B3607 SAW filters 140+/-3 MHz frontend to select 
>> only the
>> signal I am interested in).
>> It is in the decimation process that I was thinking of being in the third
>> Nyquist zone after decimation, which is incorrect because 8 MS/s is -4 to 
>> +4, so that
>> 43.05 is in the 6th Nyquist zone after decimation (\in[36:44] MHz).
> This seems weird.
> Sampling 143.05MHz at 200MHz real will produce the desired signal at 56.95MHz 
> and conjugated, won't
> it? Since it's real, it'll appear at both positive and negative frequencies, 
> with the negative
> component being conjugated.
> So if you mix with 56.95MHz, it will take the conjugated negative signal of 
> the conjugated desired
> signal and mix it to 0Hz. Then you can go through the decimation filtering 
> however you want and
> everything is centered at 0Hz.
> Right?
> Brian

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