Thank you Marcus. When I think of my application I can combine signals after demodulator where the prolblem of phase shift is not present. At the end I would like to ask what is the name of such architecture where I receive with hor and ver antennas and combine baseband signal?
On Wed, Dec 10, 2014 at 1:41 AM, Marcus D. Leech <mle...@ripnet.com> wrote: > On 12/09/2014 07:32 PM, Nemanja Savic wrote: > > is there any way to synchronize those two clocks sources? > > Not on a USRP1. > > On N200, there's support for "timed commands", which allows both > synthesizers to be locked to the same phase when they're re-tuned, but > that'll > leave you with a 0/180deg ambiguity, because the *mixer* used on the WBX > uses a 2XLO scheme, and the LO phase splitter can't be forced into > a specific state on tuning. > > Synthesized LOs have this inherent property. Even when two synthesizers > share a common reference, it's unpredictable what their phase will be > when they lock to the LO. More so for so-called fractional-N > synthesizers, which are what's used in nearly everything these days. In > the case of > the WBX and SBX, they use a synthesizer from ADI (ADF4351) that has a > fairly-rare "phase resynch" feature which allows the chip to bring the > resulting LO into a particular phase relative to the reference clock, > using a hardware synchronization signal. That signal, and the FPGA code to > make it work, is only available in the N2xx and X3xx family. The USRP1 > FPGA codebase has been utterly-frozen for many years, and there's > *zero* room to do anything fancy, without leaving stuff out. > > The usual way around this is to use a calibration signal that is common to > both receivers, and use that to calibrate-out the "per run" phase > difference. > > > > > > On Tue, Dec 9, 2014 at 4:51 PM, Marcus D. Leech <mle...@ripnet.com> wrote: > >> On 12/09/2014 04:42 AM, Nemanja Savic wrote: >> >> Shouldn't relative phase be constant and 90 degrees for example if >> transmitted wave had circular polarization? >> >> The samples will be time-aligned, but those samples will have been >> derived from two independent analog downconversion >> chains, which means that the synthesized LO will have a different >> relative phase (between the two sides) every time. >> >> >> >> >> On Tue, Dec 9, 2014 at 10:38 AM, Nemanja Savic <vlasi...@gmail.com> >> wrote: >> >>> Yes, the platform is USRP1. What is relative phase in this case if they >>> are alligned in time? >>> >>> On Mon, Dec 8, 2014 at 4:19 PM, <mle...@ripnet.com> wrote: >>> >>>> You haven't stated which USRP motherboard platform, but I assume >>>> you're talking about the USRP1, given the 4RX image. Yes, the samples >>>> will be aligned in time, but the relative phase will be random every >>>> time you re-tune or start a new session. >>>> >>>> >>>> >>>> >>>> On 2014-12-08 06:03, Nemanja Savic wrote: >>>> >>>> Hi all guys, >>>> >>>> I am about to make a receiver with two WBX daughterboards. I want to >>>> receive simultaneusly with horizontal and vertical antenna. For this >>>> purpose I want to use 4RX FPGA image. My question signals obtained in this >>>> way, from two daughterboards, alligned in time? >>>> >>>> Many thanks, >>>> >>>> -- >>>> Nemanja Savić >>>> >>>> _______________________________________________ >>>> Discuss-gnuradio mailing >>>> listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>>> >>>> >>> >>> >>> -- >>> Nemanja Savić >>> >> >> >> >> -- >> Nemanja Savić >> >> >> >> -- >> Marcus Leech >> Principal Investigator >> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org >> >> > > > -- > Nemanja Savić > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > > -- Nemanja Savić
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