[email protected] said: > For < 1ns jitter, do you have a recommendation of modulation (ASK/PSK?) and > carrier frequency?
All the digital communication over fiber that I'm familiar with is simple on-off baseband, no carrier. Digital geeks use encoding rather than modulation. One complication with fibers is that the receiver has to work with a huge dynamic range, so they all have an AGC. I don't know what the time constant on the AGC is. The other complication is that the receiving end has to do clock recovery. That requires transitions so there is a limit on the max number of consecutive 0s or 1s. Modern protocols use 8B/10B or 64B/66B to guarantee enough transitions. (Wiki pages are good.) The other goal of things like 8B/10B is an equal number of 0s and 1s so you AC couple the signal path without introducing pattern sensitivity. (The 4B/5B encoding used for FDDI had a couple of nasty cases.) The AGC makes it hard to send a simple low duty cycle PPS pulse over fiber. For something like 10 MHz, I'd send alternating 1s and 0s, at either 10 megabits or 20 megabits. Somebody has to multiply by two. I'd do it on the easier end. Suppose you want to send a PPS signal. It's easy if you have the corresponding 10 MHz clock. I'd use Manchester encoding. That is send alternating 01 at 20 megabits for the non pulse time and 10 when the PPS pulse is high. ------------- Several years ago, there was discussion (or at least mention) of the radio astronomy guys down in Chile doing clock synchronization over fibers. They had to correct for temperature and such. -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
