# Signal coming from the USRP to the computer

**URL:** <https://www.ruby-forum.com/t/signal-coming-from-the-usrp-to-the-computer/207606>\
**Category:** GNU Radio\
**Created:** [May 29, 2011, 10:52pm UTC](https://www.ruby-forum.com/t/signal-coming-from-the-usrp-to-the-computer/207606 "2011-05-29T22:52:30Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\
**Post date:** [May 29, 2011, 10:52pm UTC](https://www.ruby-forum.com/t/signal-coming-from-the-usrp-to-the-computer/207606/1 "2011-05-29T22:52:30Z")

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Hi All,  
I want to know what is the signal coming from the USRP onto the USB bus.  
I  
know that the received signal is a baseband signal and assuming complex  
sampling (I have RFX2400 daughterboards) each complex sample that enters  
the  
USB bus is the following,

x[i] = (inphase\_component) + j (quadrature\_component), and  
x[i] = m(t)cos( 2_pi_FREQ\_OFFSET_t + PHI ) + jm(t)sin(  
2_pi_FREQ\_OFFSET_t +  
PHI ), where m(t), is the actual message signal, FREQ\_OFFSET is the  
frequency offset, and PHI is the phase.

Is that correct?

Thanks

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**Author:** ![john-anes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/22d042/32.png) [@john-anes](https://www.ruby-forum.com/u/john-anes)\
**Post date:** [May 29, 2011, 11:12pm UTC](https://www.ruby-forum.com/t/signal-coming-from-the-usrp-to-the-computer/207606/2 "2011-05-29T23:12:53Z")

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On 05/29/2011 04:50 PM, John A. wrote:

> Is that correct?
> 
> Thanks

More or less, yes.

There will be random noise components as well, since this is “real  
world”, rather than purely a Matlab simulation 🙂

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

> **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)**
>
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<div class="post-metadata">

**Author:** ![john-anes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/22d042/32.png) [@john-anes](https://www.ruby-forum.com/u/john-anes)\
**Post date:** [May 29, 2011, 11:19pm UTC](https://www.ruby-forum.com/t/signal-coming-from-the-usrp-to-the-computer/207606/3 "2011-05-29T23:19:05Z")

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Of course that is true. I just wanted to make sure my understanding of  
the  
whole signal flow in GNU Radio/USRP system was right. The IF, down  
coversion  
etc stages confused me a bit. I was only interested in what I am getting  
on  
the USB bus to work with so, I wanted to make sure my understanding of  
this  
system was right.

Thanks for the reply.

---

<div class="post-metadata">

**Author:** ![john-anes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/22d042/32.png) [@john-anes](https://www.ruby-forum.com/u/john-anes)\
**Post date:** [May 29, 2011, 11:28pm UTC](https://www.ruby-forum.com/t/signal-coming-from-the-usrp-to-the-computer/207606/4 "2011-05-29T23:28:57Z")

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On 05/29/2011 05:17 PM, John A. wrote:

> Of course that is true. I just wanted to make sure my understanding of  
> the whole signal flow in GNU Radio/USRP system was right. The IF, down  
> coversion etc stages confused me a bit. I was only interested in what  
> I am getting on the USB bus to work with so, I wanted to make sure my  
> understanding of this system was right.
> 
> Thanks for the reply.

You should perhaps do a literature search on “complex downconverter” or  
“quadrature downconverter” and “direct-conversion receiver” to  
get more understanding.

With one exception, all of the daughtercards use a direct-conversion  
scheme to directly convert from RF to a complex baseband, which  
is described mathematically as you’ve shown.

I’m always nervous when I see a purely-mathematical description, because  
if you think in terms purely mathematical, without also  
considering the very-real, very-practical, you can be in for some  
surprises.

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

> **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)**
>
> Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami.