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direct sampling mode, only from signal processing view):
If you already have analog signal as separated I&Q in baseband (so called
zero-IF), and do I&Q two channel A/D converter, you can processing signal,
highest frequency of which is less than sampling rate, without aliasing.
That means, for example, you can processing signal, frequency of which is
up to 28.8MHz, when sampling rate is 28.8MHz. (There is an implicit
assumption that your zero-IF analog channel is ideal)

If you have to do sampling on a single channel analog signal( not zero-IF,
I&Q not separated by analog circuit, I&Q are still mixed together by an IF
carrier/frequency), you have to ensure the highest frequency of signal less
than half of sampling rate to ensure no aliasing.



On Wed, Jan 29, 2014 at 7:50 AM, Richard Koch <n1gp(a)hotmail.com> wrote:

> Can someone clarify what the frequency range is in Direct sampling mode.
>
> The rtl2832u dongle has a 28.8Mhz osc.
>
> So can the dongle in "direct sampling mode" (with appropriate antenna
> connection)
> receive > 14.4 Mhz (Nyquist) ?
>
> Googling I find conflicting advice.
>
> I've been able to receive > 14.4 Mhz in direct mode, but I'm not sure if
> that's due to some non-optimal method...?
>
> I'm guessing it can because the tuner chip provides both I & Q data
> therefore
> allowing the double rate...?
>
>
>
>

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<div dir=3D3D"ltr"><div><div>From the point of view of signal processing (not=
=3D
 very clear about your direct sampling mode, only from signal processing vi=3D
ew):<br></div>If you already have analog signal as separated I&amp;Q in bas=3D
eband (so called zero-IF), and do I&amp;Q two channel A/D converter, you ca=3D
n processing signal, highest frequency of which is less than sampling rate,=3D
 without aliasing.<br>
</div><div>That means, for example, you can processing signal, frequency of=3D
 which is up to 28.8MHz, when sampling rate is 28.8MHz. (There is an implic=3D
it assumption that your zero-IF analog channel is ideal)<br><br></div>If yo=3D
u have to do sampling on a single channel analog signal( not zero-IF, I&amp=3D
;Q not separated by analog circuit, I&amp;Q are still mixed together by an =3D
IF carrier/frequency), you have to ensure the highest frequency of signal l=3D
ess than half of sampling rate to ensure no aliasing.<br>
<br></div><div class=3D3D"gmail_extra"><br><br><div class=3D3D"gmail_quote">O=
n =3D
Wed, Jan 29, 2014 at 7:50 AM, Richard Koch <span dir=3D3D"ltr">&lt;<a href=3D=
3D=3D
"mailto:n1gp(a)hotmail.com" target=3D3D"_blank">n1gp(a)hotmail.com</a>&gt;</s=
pan>=3D
 wrote:<br>
<blockquote class=3D3D"gmail_quote" style=3D3D"margin:0 0 0 .8ex;border-left:=
1p=3D
x #ccc solid;padding-left:1ex">


<div><div dir=3D3D"ltr">Can someone clarify what the frequency range is in Di=
=3D
rect sampling mode.<br><br>The rtl2832u dongle has a 28.8Mhz osc. <br><br>S=3D
o can the dongle in &quot;direct sampling mode&quot; (with appropriate ante=3D
nna connection)<br>
receive &gt; 14.4 Mhz (Nyquist) ?<br><br>Googling I find conflicting advice=3D
.<br><br>I&#39;ve been able to receive &gt; 14.4 Mhz in direct mode, but I&=3D
#39;m not sure if<br>that&#39;s due to some non-optimal method...?<br><br>
I&#39;m guessing it can because the tuner chip provides both I &amp; Q data=3D
 therefore<br>allowing the double rate...?<br><br><br><br> 		 	   		  </div=3D
></div>
</blockquote></div><br></div>

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