GNSS Firehose update

Some updates on the GNSS Firehose system as it approaches general usability:

  • now supports three 50 MHz RF channels (nominally covering L1/L2/E5), 840 Mbit/s total payload
  • supports command and status over Ethernet (in addition to UART)
  • firmware now in C, running on a RISC-V soft CPU (picorv32 from Clifford Wolf)
  • change over to KiCad for schematic and PCB layout

The enclosure is the same as before, a Hammond 1455L1201, with fancier artwork this time:

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A run of 20 boards was assembled, with a very pleasant yield of 100% (thanks, Sparqtron!). Here’s a shot of some of them. They have yet to receive the small 3D-printed plastic cap for the TCXO. That turns out to be quite important to reduce air currents near the device—it dramatically improves the performance of the local clock, so that, for a reasonably strong signal, there’s only the occasional excursion of 1 Hz or so over timescales of a few seconds. (I should make an Allan-variance plot from one of the PLL tracks.)

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