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List: usrp-users
Subject: Re: [USRP-users] Questions on band-pass filtering and AGC
From: Marcus_Müller via USRP-users <usrp-users () lists ! ettus ! com>
Date: 2014-08-29 21:48:56
Message-ID: 5400F548.7090706 () ettus ! com
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Hi Khalid,
Marcus referred to the 30MHz filter of the LFRX; there's no analog
circuitry between a daughterboard and the ADC.
The general architecture of the N200 is the following: There's the
analog frontend on the daughterboard, which always must include a
bandpass of less than 100MHz width (exception: BasicRX, which is not
"really" a fully fledged daughterboard). The filtered (and mixed) signal
goes straight to the ADC, where it is sampled at 100MS/s. Then, in the
FPGA, anti-aliasing filtering for the decimation is applied, and the
signal is decimated to the sampling rate you request.
Greetings,
Marcus
On 29.08.2014 20:03, khalid.el-darymli via USRP-users wrote:
> Thanks Marcus for the quick answer. Now I am interested in a particular
> bandwidth at the baseband. That is in the vicinity of my FMCW chirp
> bandwidth. Say for example 200 KHz. When the signal is received and
> digitized by the N200 unit, is there a kind of *analog *low-pass filter
> implemented in the N200 such that it only passes my bandwidth of interest
> and it filters-out the out of band frequencies. Am I right to say that this
> analog low-pass filter is configurable by the sampling rate specified in
> the UHD:USRP Source Block? Or rather, there is no such analog filter at all?
>
>
> Thank you.
>
> Best regards,
> Khalid
>
>
> On Fri, Aug 29, 2014 at 2:23 PM, <mleech@ripnet.com> wrote:
>
> > The LFRX has a 30Mhz low-pass response, but it isn't very sharp. In
> > order to reduce aliases, I would recommend "stiffening" that low-pass
> >
> > response with an external filter.
> >
> >
> >
> > There is no AGC on the LFRX. It has a buffer amplifier on it that exists
> > largely to convert from unbalanced to balanced, and provide a
> >
> > low-order 30Mhz low-pass response.
> >
> >
> >
> >
> >
> >
> >
> >
> > On 2014-08-29 12:48, khalid.el-darymli via USRP-users wrote:
> >
> > Dear all,
> >
> > I am using N200 with the LFRX daughterboard as a receiver (HF radar). I
> > have two questions.
> >
> > *Firstly*, do I have to use an analog band-pass filter to reject the out
> > of band interference as explained in this link:
> > http://www.ettus.com/content/files/kb/application_note_receiving_hf_signals_with_a_usrp_device.pdf
> > ?
> >
> >
> > My* second question* is about '*analog' *automatic gain control (AGC).
> > Does the LFRX/N200 implement AGC? If so, what is the AGC method used? Can
> > it be disabled?
> >
> >
> > Thank you.
> >
> > Best regards,
> > Khalid
> >
> >
> > _______________________________________________
> > USRP-users mailing \
> > listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
> >
> >
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users@lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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Hi Khalid,<br>
<br>
Marcus referred to the 30MHz filter of the LFRX; there's no analog
circuitry between a daughterboard and the ADC.<br>
The general architecture of the N200 is the following: There's the
analog frontend on the daughterboard, which always must include a
bandpass of less than 100MHz width (exception: BasicRX, which is not
"really" a fully fledged daughterboard). The filtered (and mixed)
signal goes straight to the ADC, where it is sampled at 100MS/s.
Then, in the FPGA, anti-aliasing filtering for the decimation is
applied, and the signal is decimated to the sampling rate you
request.<br>
<br>
Greetings,<br>
Marcus<br>
<br>
<br>
<div class="moz-cite-prefix">On 29.08.2014 20:03, khalid.el-darymli
via USRP-users wrote:<br>
</div>
<blockquote
cite="mid:CACdmG=zCetLJ=9zWJvxHXZSymX=k47XZh1OESyKf7Ez7DkgAmQ@mail.gmail.com"
type="cite">
<pre wrap="">Thanks Marcus for the quick answer. Now I am interested in a \
particular bandwidth at the baseband. That is in the vicinity of my FMCW chirp
bandwidth. Say for example 200 KHz. When the signal is received and
digitized by the N200 unit, is there a kind of *analog *low-pass filter
implemented in the N200 such that it only passes my bandwidth of interest
and it filters-out the out of band frequencies. Am I right to say that this
analog low-pass filter is configurable by the sampling rate specified in
the UHD:USRP Source Block? Or rather, there is no such analog filter at all?
Thank you.
Best regards,
Khalid
On Fri, Aug 29, 2014 at 2:23 PM, <a class="moz-txt-link-rfc2396E" \
href="mailto:mleech@ripnet.com"><mleech@ripnet.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap=""> The LFRX has a 30Mhz low-pass response, but it isn't very \
sharp. In order to reduce aliases, I would recommend "stiffening" that low-pass
response with an external filter.
There is no AGC on the LFRX. It has a buffer amplifier on it that exists
largely to convert from unbalanced to balanced, and provide a
low-order 30Mhz low-pass response.
On 2014-08-29 12:48, khalid.el-darymli via USRP-users wrote:
Dear all,
I am using N200 with the LFRX daughterboard as a receiver (HF radar). I
have two questions.
*Firstly*, do I have to use an analog band-pass filter to reject the out
of band interference as explained in this link:
<a class="moz-txt-link-freetext" \
href="http://www.ettus.com/content/files/kb/application_note_receiving_hf_signals_with \
_a_usrp_device.pdf">http://www.ettus.com/content/files/kb/application_note_receiving_hf_signals_with_a_usrp_device.pdf</a>
?
My* second question* is about '*analog' *automatic gain control (AGC).
Does the LFRX/N200 implement AGC? If so, what is the AGC method used? Can
it be disabled?
Thank you.
Best regards,
Khalid
_______________________________________________
USRP-users mailing <a class="moz-txt-link-abbreviated" \
href="mailto:listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usr \
p-users_lists.ettus.com">listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com</a>
</pre>
</blockquote>
<pre wrap="">
</pre>
<br>
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<br>
<pre wrap="">_______________________________________________
USRP-users mailing list
<a class="moz-txt-link-abbreviated" \
href="mailto:USRP-users@lists.ettus.com">USRP-users@lists.ettus.com</a> <a \
class="moz-txt-link-freetext" \
href="http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com">http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com</a>
</pre>
</blockquote>
<br>
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