On Sat, Nov 13, 2010 at 10:41 AM, tom_wgs <tom.r...@wgssystems.com> wrote: > > > tom_wgs wrote: >> >> >> >> tom_wgs wrote: >>> >>> Hi all >>> ... >>> .. >>> Thank you for your time and any help would be very much appreciated. >>> Tom >>> >> >> I have attached a couple additional plots showing the results of taking >> 128 complex points at 500 kHz sampling rate from channel 2, and dividing >> it (complex) by the same number of complex points from channel 1 >> (element-by-element division, or complex mixing). >> >> .... >> ... >> . >> >> http://old.nabble.com/file/p30202507/Time%2BDomain%2BFreq%2B%2526%2Bother%2Berrors.jpg >> >> http://old.nabble.com/file/p30202507/RXA_norm_RXB_Time_Domain.jpg >> >> > > I found a partial solution but am not sure why and if my problem is > completely fixed. I found that the Charge pump setting (_set_cp(int) was > being set to 2 different values at 1880mHz for the 2 receivers. After > experimenting the best results come when forcing the values both to 1 for > all tested frequencies. > > The results can be seen below. Compare this to the results previous > provided above. Can anyone provide some information on the charge pump and > how the settings effect the receiver. >
Interesting results, there is an application note (max2116 AN02-R0) that can be requested from Maxim regarding how to select VCOs when tuning the max2118. It indicates that the Vtune voltage for the selected VCO should be read (_max2118_read_regs.adc) and the value used to select the best charge pump current. That is what was implemented at: http://ettus-apps.sourcerepo.com/redmine/ettus/projects/uhd/repository/revisions/master/entry/host/lib/usrp/dboard/db_dbsrx.cpp#L383 Could you set dbsrx_debug to true on line 46 of db_dbsrx.cpp and rebuild and install UHD. Then look for output lines like: DBSRX: final vco %d, vtune adc %d and see what VCO and Vtune voltage is achieved on each DBSRX. It is possible that your frequency of choice falls on the edge of a VCO band for the DBSRX, and thus you get different settings. But if the DBSRX is locked, I would not think the difference in charge pump current would cause varying phase offsets. Jason _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
