Hi, Sorry for late reply. I was running out of time, so I used the offset tune future of UHD to handle that spike. See the following link, hope it helps,
http://files.ettus.com/manual/structuhd_1_1tune__request__t.html -- Bob On Sat, Apr 2, 2016 at 7:41 AM, hanwen <kidult.han...@gmail.com> wrote: > Hi Bob, > > I came up with the same issue and I hope the DC leakage from Tx should > disappear right after the Tx burst is finished, but acturally I still saw > the strong DC during the pure Rx time lot. > Have you got a solution for that? Thanks. > > Br, Hanwen > > 2014-10-31 7:31 GMT+01:00 bob wole <bnw...@gmail.com>: > >> >> >> >> On 10/29/2014 01:54 PM, bob wole via USRP-users wrote: >>> > >>> > USRPN210r4 with SBX >>> > >>> > I am observing a strong spike at the center of the receive spectrum >>> > when I start burst transmission. >>> > >>> > My top flowgraph contains following two hierarchical blocks >>> > 1) A transmitter flow graph with (tx_time, tx_sob, tx_eob) >>> > 2) A receiver flow graph >>> > >>> > When I run top flowgrpah (without transmitting anything) and observe >>> > the FFT of the received signal the spectrum does not contain high >>> > spike in the center. >>> > >>> > But as soon as I start transmitting in burst mode I see a very high >>> > spike in center of the received signal FFT spectrum. It looks like LO >>> > (transmitter or receiver ) is being received? Which one is it ? And >>> > why is it happening? How can I avoid it because it is affecting my >>> > packets. >>> > >>> > When I apply the offset in digital using DDC/DUC, the spike moves out >>> > of the band. >>> > >>> > >>> > -- >>> > Bob >>> > >>> > >>> > _______________________________________________ >>> > USRP-users mailing list >>> > usrp-us...@lists.ettus.com >>> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> That spike in the middle is a consequence of using direct conversion in >>> both the RX and TX paths--it'll be there in both to some degree. >>> >>> You can use offset-tuning to move the DC offset outside your passband: >>> >>> http://files.ettus.com/manual/page_general.html >>> >>> >>> In built-for-a-particular-purpose radios, there will also be undesired >>> LO leakage and mixing products--those are generally dealt with using an >>> application/band-specific filter to eliminate them. For >>> general-purpose SDRs, that isn't possible to do "as manufactured", you >>> have to deal >>> with RF hygiene and plumbing issues yourself. >>> >>> So, moving the LO leakage outside your passband is part of the >>> picture--use offset tuning for that. Then, if you have "this won't meet >>> our hygiene requirements", you have to look at filtering. >>> >>> Another thing you really should do is to run the calibration utilities, >>> which will attempt to balance I/Q amplitude and phase, which can improve >>> some of these issues, but not, usually, eliminate them entirely. >>> >>> >>> >> 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. >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
