# Problems with DC offsets, leakage and other stuff

**URL:** <https://www.ruby-forum.com/t/problems-with-dc-offsets-leakage-and-other-stuff/218936>\
**Category:** GNU Radio\
**Created:** [April 16, 2012, 9:45pm UTC](https://www.ruby-forum.com/t/problems-with-dc-offsets-leakage-and-other-stuff/218936 "2012-04-16T21:45:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Gurdipe\_D](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/b77776/32.png) [@Gurdipe\_D](https://www.ruby-forum.com/u/Gurdipe_D)\
**Post date:** [April 16, 2012, 9:45pm UTC](https://www.ruby-forum.com/t/problems-with-dc-offsets-leakage-and-other-stuff/218936/1 "2012-04-16T21:45:27Z")

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Hi,

This is a problem I have been having for a while, but I’ve never given  
it  
enough importance until now.

Basically I have a USRP2 as a receiver and no transmitter. So basically,  
I  
am just measuring noise.  
I am using the 5GHz band.

Here are the fft plots for freq. 5GHz and gain 30 and 50.  
[http://old.nabble.com/file/p33690634/pic1.jpg](http://old.nabble.com/file/p33690634/pic1.jpg)  
[http://old.nabble.com/file/p33690634/pic2.jpg](http://old.nabble.com/file/p33690634/pic2.jpg)

As you can see the peak at center frequency is eliminated by changing  
the  
gain. So I guess it was just some DC offset that wasn’t removed by the  
USRP.  
However, the other peak at -30kHz approximately remains. I tried to use  
uhd.tune\_request thinking it was some leakage but the peak doesn’t move.

When I use a center freq. greater than 5GHz and lesser than 5.5GHz I get  
this: [http://old.nabble.com/file/p33690634/pic3.jpg](http://old.nabble.com/file/p33690634/pic3.jpg)  
[http://old.nabble.com/file/p33690634/pic4.jpg](http://old.nabble.com/file/p33690634/pic4.jpg)

In this case I have a peak at center frequency which isn’t attenuated  
even  
if I change the gain. The peak at -30kHz remains also. I tried using the  
uhd.tune\_request treating these peaks as leakage but they didn’t move at  
all  
once more.

At 5.5GHz, I don’t have any peak (I don’t think it is necessary to post  
a  
image in this case) except for a small DC offset which is eliminated  
with a  
increase in the gain.  
The peak at the center frequency (but not the -30kHz peak), however,  
appears  
again for frequencies greater than 5.5GHz but less than 6 GHz.

## Someone answered me in another post about the leakage problem and how to solve it. However, those tools are not working in this case.

View this message in context:  
[http://old.nabble.com/Problems-with-DC-offsets%2C-leakage-and-other-stuff-tp33690634p33690634.html](http://old.nabble.com/Problems-with-DC-offsets%2C-leakage-and-other-stuff-tp33690634p33690634.html)  
Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).

---

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**Author:** ![frankist](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e36b37/32.png) [@frankist](https://www.ruby-forum.com/u/frankist)\
**Post date:** [April 17, 2012, 7:42pm UTC](https://www.ruby-forum.com/t/problems-with-dc-offsets-leakage-and-other-stuff/218936/2 "2012-04-17T19:42:24Z")

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On Mon, Apr 16, 2012 at 12:44, frankist [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> This is a problem I have been having for a while, but I’ve never given it  
> enough importance until now.

As this is focused on the USRP, you may find more help available by  
posting to the USRP users list.

Johnathan