Various people remarked on the noisy and wide line synch pulse displayed on the Tek 529 waveform monitor when I demonstrated the FOTH standards converter at Harpenden last weekend.
A little investigation has shown that this is due to the XOR synch combiner, the synch pulse is stretched by the cpacitance in the combiner circuit (this is used to allow positive or negative going synch pulses without altering the circuit), and the noise seen in the bottom of the "stretched" pulse is coincident with the end of the input pulse - I suspect this is due to poor screening and excessive cpacitance in my construction (I'll admit it Jeffrey, I shouldn't have used stripboard
).
I think the definitive cure is to remove the capacitance from the input of the synch combiner, and rely on the X-config modeline to set the synch polarity correctly. Altering the capacitor value would improve matters, but only for one particular standard. Of course the ideal solution would be to completley redesign the synch combiner to properly regenerate the synch for the relevant standard.
Jim.