Nexedi is the main provider of ORS hardware for RapidSpace.
Nexedi is manufacturing the SDR PCB for the ORS in France with electronic components coming from various suppliers. This PCB has a bit more than 800 electronic components with 127 different references.
What happened ?
In July 2022, we couldn't find anymore the VCXO (Voltage controlled oscillator) from Abracon we used on our previous PCBs (ASVTX-12-A-38.400MHZ-H10-T). It was not in stock with our regular suppliers.
We decided to order on Alibaba to a vendor called Techkeys Electronics 100 pieces of this component.
We started to solder this part on all our PCBs at that date (July 2022) and we did so for all our PCBs until today (Sept 2023). The part we received was not correct and instead of being a voltage controlled oscillator, we got a regular oscillator with an enable pin.
marking of the bad VCXO
marking of the good VCXO
What are the consequences ?
The ORS SDR boards that we ship work for 99% of use cases. LTE works. NR works. Core network works. Handover works if two frequencies are used etc. We could reach 3km range in line of sight. Overall, the ORS we shipped are a big improvement over the previous versions.
Yet, the use of this "bad" component leads to 2 main consequences: the oscillator doesn't produce a clock at the boot, we need to enable it before it produces a clock and we cannot sync the clock on the GPS.
No clock at boot time
The problems to not have any clock at boot time are:
- We can't rely on that clock to clock the FPGA. Since our firmware was using this external clock to boot, we couldn't boot properly anymore. At the time we didn't investigate why there was no clock and we decided to boot from an internal clock of the FPGA instead.
- We cannot load the kernel driver from Amarisoft starting from version 2022-03-17. At the time of the problem we were still using kernel driver version 2021-12-17 so we didn't see the problem. Also, when we started using newer version of Amarisoft, we realized that loading kernel driver 2021-12-17 priori to load a newer kernel module worked fine so we used that solution until now. Note that it worked because loading the kernel driver 2021-12-17 once will make the FPGA enable the oscillator.
No voltage controlled clock
Since the oscillator is not actually voltage controlled, it is not possible to sync it to GPS clock. So it means we cannot use 2 ORS in the same location with the same frequency.
What will we do ?
For all our customers wanting to use the GPS clock, we will ask them to send back their ORS so that we can replace the wrong part with a new one. Since there is still a shortage of Abracon's VCXO, we decided to use Taitien's oscillator: TYETBLSANF-38.400000 (see https://www.taitien.com/wp-content/uploads/2015/12/XO-0081_TY.pdf). This part is available on digikey : https://www.digikey.fr/en/products/detail/taitien/TYETBLSANF-38-400000/6127660 and we are currently testing it.
We will start contacting our customers this week.