I'm trying to evaluate the quality of an 8b/10b encoded data stream (Gigabit Ethernet, 1.25 gigabits/sec). Without doing clock recovery from the data stream, I want to measure jitter (et al) with a plain oscilliscope. Is there any 8b data stream I can send which ends up as a regular square wave in 10b format? I don't care it's divided or uneven duty cycle, as long as it's a regular grouping of 0's and 1's.
Alternating pattern for 8b10b encoding is D10.2 symbol. Check out table in wikipedia.
However this may not be what you want as for example gigabit Ethernet of the 1000BASE-T flavor uses PAM-5 modulation with data scrambling instead of NRZ with 8b10b encoding (again Wikipedia is helpful).
Also end result will depend in which protocol layer you are injecting test data as different protocol layers will add/remove/modify data.