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
