# Two WBX boards synchronization **URL:** \ **Category:** GNU Radio\ **Created:** [December 8, 2014, 12:04pm UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369 "2014-12-08T12:04:49Z")\ **Posts on this page:** 8\ **Page:** 1
**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:** [December 8, 2014, 12:04pm UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/1 "2014-12-08T12:04:49Z")
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, ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 8, 2014, 4:21pm UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/2 "2014-12-08T16:21:29Z")
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 S. wrote: > * * * > > Discuss-gnuradio mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) [1] Links: ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 9, 2014, 10:39am UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/3 "2014-12-09T10:39:19Z")
Yes, the platform is USRP1. What is relative phase in this case if they are alligned in time? ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 9, 2014, 10:44am UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/4 "2014-12-09T10:44:13Z")
Shouldn’t relative phase be constant and 90 degrees for example if transmitted wave had circular polarization? ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 9, 2014, 4:53pm UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/5 "2014-12-09T16:53:10Z")
On 12/09/2014 04:42 AM, Nemanja S. 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. ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 10, 2014, 1:33am UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/6 "2014-12-10T01:33:51Z")
is there any way to synchronize those two clocks sources? ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 10, 2014, 1:43am UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/7 "2014-12-10T01:43:39Z")
On 12/09/2014 07:32 PM, Nemanja S. 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. ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [December 10, 2014, 9:59am UTC](https://www.ruby-forum.com/t/two-wbx-boards-synchronization/233369/8 "2014-12-10T09:59:43Z")
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?