[1]https://hackaday.com/2022/04/01/a-gang-of-hackrfs-makes-for-a-wideband-sdr/

   (Oleg Kutkov] decided to [2]build a wideband SDR – for satellite
   communication research and monitoring, you know, the usual. He decided
   on a battery of HackRF boards – entire eight of them, in fact. Two 1×4
   and one 1×2 RF splitters and an LNA on their combined RF input made for
   a good start to the project, and from there, it only got more complex.

   HackRF boards can be synchronized with a separate clock source, but you
   can’t just pull a single clock line to all of them in a star
   configuration. Thus, he’s built [3]a clock distribution and amplifier
   board, with 4 ns propagation delay at 1 PPS, and only 10 ns delay at 10
   MHz. Then, he [4]integrated that board with the HackRF setup, adding a
   case, wiring up a purpose-built cable and dealing with the reflections
   that occurred.

   HackRF boards are USB 2.0 and able to generate a stream of data up to
   320 MB/s, and there’d be no viable way to [5]aggregate eight 2.0 links
   into one. To solve that, he’s used eight separate PCI-E to USB 3.0
   cards, each of them with one HackRF plugged in, all connected to an AMD
   Ryzen 9-powered PC through PCI-E risers we typically see used for
   mining purposes. To tie it all together, he created a gnuradio
   flowgraph and patched the osmocom source block to enable the external
   clock synchronization mechanisms he decided to use.

References

   1. https://hackaday.com/2022/04/01/a-gang-of-hackrfs-makes-for-a-wideband-sdr/
   2. https://olegkutkov.me/2021/11/29/hackrf-supercluster/
   3. https://olegkutkov.me/2021/04/10/1pps-square-clock-8-channel-distribution-amplifier/
   4. https://olegkutkov.me/2021/08/19/housing-for-the-1pps-square-clock-8-channel-distribution-amplifier/
   5. https://hackaday.com/2022/03/07/a-chip-to-address-the-fundamental-usb-3-0-deficiency/