Baird 240 line Operation

[peter scott]

The graphics card syncs do differ in two respects from the EMI 405 line standard and this can cause rather critical line frequency adjustment or hooking at the top of the picture in older sets that don't have flywheel sync. Sorting this is work in progress. The existing composite sync is simply generated by exclusive OR of the line and frame pulses but the resulting inverted line pulses within the frame sync are slightly delayed relative to their correct positions. There is also no half line pulse stream. The latter is not essential and a simple monostable circuit can correct the pulse positions. See Here. To use this circuit the Modelines need to be changed such that the Composite Sync box should be unticked and the +hsync references should become -hsync.

Peter