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]<mailto:[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]<mailto:[email protected]> To unsubscribe send an email to [email protected]<mailto:[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]<mailto:[email protected]> To unsubscribe send an email to [email protected]<mailto:[email protected]>
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