14-11-2016, 07:22 PM
Hi.
I got about an hour on the project today. I added an extra stage after the 555 to invert the waveform and hopefully cure the small amount of cramping on the bottom of the scan.
David Boynes suggested replacing the electrolytic charging cap with a non electrolytic type, I duly did this and there was a small improvement on 25i scan, 25p was no better though. Adding the stage certainly gave me phase reversal but the linearity is awful. My feeling is using a bipolar device is wrong so I'm going to use a FET instead, I think its all down to the impedance matching.
I'll have another fiddle tomorrow.
Incidentally all standards are excellent down to 180/25p, Ill post up pictures of the test cards and also some pictures with program material. Some of the fully mechanical systems can be resolved but I need to sort out the syncs on them with a different approach as the LM1881 isn't happy.
I got about an hour on the project today. I added an extra stage after the 555 to invert the waveform and hopefully cure the small amount of cramping on the bottom of the scan.
David Boynes suggested replacing the electrolytic charging cap with a non electrolytic type, I duly did this and there was a small improvement on 25i scan, 25p was no better though. Adding the stage certainly gave me phase reversal but the linearity is awful. My feeling is using a bipolar device is wrong so I'm going to use a FET instead, I think its all down to the impedance matching.
I'll have another fiddle tomorrow.
Incidentally all standards are excellent down to 180/25p, Ill post up pictures of the test cards and also some pictures with program material. Some of the fully mechanical systems can be resolved but I need to sort out the syncs on them with a different approach as the LM1881 isn't happy.
