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> On 02/18/2026 8:29 PM CST Chris Wozny <[email protected]> wrote: > > > We're working on a two-channel phase interferometry application using an X410 > with two ZBX daughterboards and am having difficulty achieving consistent > inter-channel phase measurements across application restarts. I'm hoping > someone on the list has experience with this and can point me in the right > direction. I've found quite a few emails on the mailing list from about a > year ago on the topic, but they didn't seem to have a resolution (as far as I > could tell). > > Here's my current configuration: > > NI USRP X410 (Rev 7) > Two ZBX daughterboards > MPM Version: 5.3 > FPGA Version: 8.3 (UC_200) > FPGA git hash: c37b318.clean > > I'm using UHD 4.7.0.0 with the Multi_USRP API in C++. The ports I'm connected > to are the RX1 SMA ports on the same daughterboard (A:0 and A:1). The X410 is > also connected to an external 10 MHz + 1 PPS reference from an Octoclock. I'm > feeding these receive ports with a pulsed waveform from a signal generator > connected via a splitter. > > Problem: > > Within a single execution of the application, the phase difference between > the two channels is extremely stable and consistent pulse-to-pulse. However, > when the application is restarted the phase offset changes to an essentially > arbitrary value. Across five consecutive runs we observed delta phase values > of approximately -25, -154, -25, 74, and -119 degrees at 3050 MHz. > > The same code (timed command tune requests) and test equipment setup was > working with an X310. The phase differences were consistent over a period of > a few days of application restarts and power cycles. It seems like there are > some fundamental architectural differences between the X310 with two UBX-160s > and the X410 with two ZBXs that prevent the same task from being accomplished. > > Here are the steps we've taken thus far to try and get the same initial phase > on both channels from one run of the application to another: > > 1. Switched clock and time source to "external" to lock to the Octoclock's 10 > MHz and 1 PPS reference and polled the ref_locked sensor before proceeding. > 2. Used set_time_next_pps() rather than set_time_now() to latch device time > on a PPS edge, followed by a sleep longer than one second to guarantee the > latch has occurred. > 3. Configured subdev spec (A:0 A:1), per-channel parameters (sample rate, > bandwidth, gain, antenna), and get_rx_stream() all after the ref_locked wait > and PPS latch. > 4. Issued simultaneous tune commands to both channels using > set_command_time() aligned to the next PPS edge > (get_time_now().get_full_secs() + 1.0), followed by another sleep greater > than 1 second to allow LO lock. > 5. Attempted explicit LO sharing via set_rx_lo_source("internal", > "LO1"/"LO2", chan) on both channels, however set_rx_lo_export_enabled() was > not supported on this radio so we abandoned that. > > The within-run phase stability is excellent (sub-degree variation > pulse-to-pulse), which suggests the hardware is working correctly. The > problem appears to be that something is initializing to an arbitrary phase > state on each UHD session that is not being reset by any of the above steps. > > The ultimate question we have: with an X410 and two ZBX daughterboards is > multi-channel phase coherence across multiple UHD sessions possible? If so, > are there any steps we might be missing or out of order from what we tried > above? Feeding in a known signal every time we start a session is not an > option. > > There was some chatter in the mailing list about newer versions of UHD > resolving this, but other replies from March 2025 left it ambiguous (to me at > least) as to whether this was fixed for X410s or X440s or fixed at all. > > Any guidance you all might provide is greatly appreciated! > > Best, > Chris > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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