It is essential that 10MHz signal fed to the 001-0131 Fiber Optic Transmission system is terminated in 50 ohm. Failure to do so will cause the system to operate in an mode whereby the output 10 MHZ and associated 1PPS is not locked to the source 1PPS and 10 MHz.

The symptom of this condition is that 1PPS appears to "precess" relative to the source 1PPS. The locked LED will also not be illuminated.