We have a setup with two USRP devices, attempting to acquire signals' time of arrival (TOA) with matched filters. We can observe stable and accurate TOA using USB-driven devices (i.e., B210's) with a single external PPS and 10MHz feed.
However, when testing the design with two E320's using their integrated GPSDO as the clock and timing source, we could not achieve a steady TOA anywhere close to the clock performance specified [here](https://www.ettus.com/wp-content/uploads/2019/01/USRP_E320_Datasheet.pdf "https://www.ettus.com/wp-content/uploads/2019/01/USRP_E320_Datasheet.pdf";). A constant drift over time (i.e., +50 ns over \~120 seconds) was observed on one E320 device with respect to the other for each run. We are almost certain that neither of the devices is damaged (they are fresh out of the box), also we are aware of [this](https://lists.ettus.com/empathy/thread/EDXCIKFY5LW7IEQN2JZOGXGWNCBELU3F?hash=4KGAPCNGJL6WXKC4IBZBITVNSFTDXXRK#4KGAPCNGJL6WXKC4IBZBITVNSFTDXXRK "https://lists.ettus.com/empathy/thread/EDXCIKFY5LW7IEQN2JZOGXGWNCBELU3F?hash=4KGAPCNGJL6WXKC4IBZBITVNSFTDXXRK#4KGAPCNGJL6WXKC4IBZBITVNSFTDXXRK";) issue. The setup includes one source signal symmetrically fed to the devices from the same RF channels. The E320 devices share the same GPS antenna, which is an externally fed active GPS antenna while the E320 GPSDO's ports are DC blocked. We are yet to try: 1. Observing the behavior with another pair of E320 devices. 2. Feeding the source signal from the other RF ends. 3. Synchronizing the E320's with an external clock and timer, as we have done with the B210 devices. We are wondering if there are any software tricks applicable specific to the E320 devices that we should be employing. Any help will be appreciated!
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