|
B&W television in the early days at local tv stations were commonly locked locked to 60Hz power line to synchronize the 16mm film projector shutter to the blanking time in video, due to wide use of iconoscopes for film. Into 1960’s. With vidicons for film this issue went away and the projector could be non synchronous with the film shutter.
You could also lock the mono sync gen to its internal 94.5 khz crystal (3 x 31.5) if you had unstable 60hz, or no synchronous film projectors.
Lock to 60 Hz also helped with hum bars floating through due to various sources of 60 hz ac in video, so that any ‘ hum bars’ were stationary on home receivers.
During any major network show coming in on ATT microwave, the station just switched to the net source and all home receivers tuned in would do a vertical roll since the network and local station vertical sync had random relationship. Coming from network back to the local station, the tv station operator would take ‘black’ momentarily first so all home receivers would roll in black then punch the local station source. Going from local to network that doesn’t work, so the switch always caused a roll at home. Crude, but that’s the way it was.
The big glitch and roll was due to the random vertical sync relationship between local station sync and network sync, NOT due to the minor change in sync rates. This happened with mono as well as color.
BTW, Frame sync’s weren’t until mid 70’s and cost a fortune due to the 3MB digital memory.
Genlock on a sync gen could be added (an option) but local station didn’t stations didn’t stay genlocked to network feed because any disturbance on the network would cause your whole station sync to ‘glitch’ sync. If you were recording locally on videotape this disturbance caused a huge glitch in the recording.
No one at a local station or at home even noticed if the network were sending color unless you had a color monitor, or noticed the color burst on a scope. The color H &V rate changes had no effect since by intent they were so close to mono standards.
|