# Re: \[USRP-users\] Switching and high spike in spectrum

**URL:** <https://www.ruby-forum.com/t/re-usrp-users-switching-and-high-spike-in-spectrum/232855>\
**Category:** GNU Radio\
**Created:** [October 31, 2014, 6:33pm UTC](https://www.ruby-forum.com/t/re-usrp-users-switching-and-high-spike-in-spectrum/232855 "2014-10-31T18:33:07Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [October 31, 2014, 6:33pm UTC](https://www.ruby-forum.com/t/re-usrp-users-switching-and-high-spike-in-spectrum/232855/1 "2014-10-31T18:33:07Z")

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On 10/29/2014 01:54 PM, bob wole via USRP-users wrote:

> > When I run top flowgrpah (without transmitting anything) and observe  
> > of the band.  
> > That spike in the middle is a consequence of using direct conversion in  
> > general-purpose SDRs, that isn’t possible to do “as manufactured”, you

Yes, I know that LO leakage/DC offset is an issue present in direct  
conversion receiver. But as I mentioned earlier, the received spectrum  
looks fine (a very little spike at DC around -70dB) while the burst  
transmission is not running. The spike becomes much more significant (  
high  
spike at DC -20dB) when burst transmission (tx\_time,tx\_eob, tx\_sob )  
starts and all the spectrum just shifts up and down with it. I am using  
TX/RX antenna in both usrp source and usrp sink. I want to know why the  
burst transmission is affecting the received spectrum on the same node.