Hi David, I've researched this before with the earlier model b200-mini. As a retail customer without the deeper resources and knowledge of our esteemed hosts, I'd characterize the project as follows:
Net-net, to incorporate both PPS and 10MHz REF in a b200-mini ( *hackily-at-best**) invokes cost, complexity, and *time spent*** to such a degree that less resources are involved in purchasing a B-210 (not a typo), possibly two B210s (also not a typo). *Footnotes:* * *Hackily-at-best* includes the nonzero probability of smoking your b200-mini. ***Cost of time spent* assumes you value your labor at "McDonald's-high-school-summer-job-level" wages or higher. *.--* Walter Alden Tackett 415 407 0660 [email protected] On Thu, Jan 15, 2026 at 8:37 AM David Raeman via USRP-users < [email protected]> wrote: > Martin and Marcus, > > > > Thank you both very much for the feedback. For this application, when not > attached to the Octoclock, I use a high quality OCXO reference and I need > somewhat stable, trackable relative phase drift characteristics between > radios. I didn’t realize the minis lack a dedicated hardware PLL and rely > only on a digital control loop. It sounds like the high stochastic jitter > could indeed be problematic for me and is an unavoidable limitation of the > small form-factor USRPs. > > > > I’ll still poke at it a bit, but I very much appreciate the heads-up! > > -David > > > > > > *From:* Martin Braun <[email protected]> > *Sent:* Thursday, January 15, 2026 3:47 AM > *Cc:* [email protected] > *Subject:* [USRP-users] Re: Using USRP B206mini with Octoclock 10MHz+PPS > > > > Hey David, > > > > to add onto what Marcus said: The minis don't have a hardware PLL (unlike > the B200/B210, and all other USRPs). Before you go down the rabbit hole of > modifying the FPGA, you might want to run a few B2xx-minis from an > Octoclock (ignore PPS for now), and check if the phase stability is good > enough for your application. > > > > Other than that, it would be possible to use a GPIO input for PPS, but > neither the software nor the FPGA expect that, and both will require > modifications. For a USRP/UHD veteran such as yourself, that sounds > feasible, but be aware it's a lot of work and might not give you what you > need. > > > > --M > > > > On Wed, Jan 14, 2026 at 9:20 PM Marcus D. Leech <[email protected]> > wrote: > > On 2026-01-14 14:57, David Raeman via USRP-users wrote: > > Hello, > > > > I have a project currently hosted on a USRP E320 that involves distributed > signal coherence. During development I sometimes do over-the-wire testing > using an Octoclock’s 10MHz and PPS outputs to synchronize multiple radios > on the bench. > > > > I’m starting to investigate the viability of rehosting this application on > a USRP B206mini to reduce size and cost. As far as I can discern, this > radio only has a single port that can accept either a 10MHz reference input > or a PPS input. Is it possible to somehow use the radio with both clock and > PPS outputs from an Octoclock with out-of-the-box UHD? If not, would it be > viable for me to add a bit of FPGA logic and UHD tweaks such that software > can specify a GPIO pin as the PPS input while using the SMA as the 10MHz > input? Or are there hardware or systems constraints that would preclude > that approach? > > > > Thanks! > > David Raeman > > Synoptic Engineering > > > > _______________________________________________ > > USRP-users mailing list -- [email protected] > > To unsubscribe send an email to [email protected] > > You could probably add some FPGA functionality to implement a separate PPS > input. > > But I should warn you that the clock servo in the B205x series is simply > NOT UP TO THE TASK of building-out multi-unit coherent applications. > > The mutual phase-noise is way too high. The B205 was never intended for > such applications to begin with, and the clock servo just doesn't work that > well. > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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