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Thread: Having trouble with LM1881 / NTSC sync separator
www.piclist.com/techref/displays.htm?key=ntsc
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face BY : Peter Wintulich email (remove spam text)



The CRO signal may be missleading, you need to check if the is set to ALTernate or CHOP. You need CHOP to check that the video is in phase, ALT will always show the two signals in sync as it triggers for each chanel. Some CRO's chose between these modes depending on the trace sweep speed.
What other connections are visable between the cameras ? ie SYNC, power, GEN. etc, or are the two cameras boxed together? What are the connectors on the camera labeled as, please include the ones that don't have anything attached.
If they are studio or scientific cameras then there may be one thick cable leading to the camera from a power/ signal management box where signals like Genlock or Sync may be accesable.

From what has been said you will need to terminate both camera video outputs at your switcher box (75 ohms),
using 2 4066 gates & an inverter gate build an A/B analoug switch,
the output of the analoug switch should go into a buffer amplifier with a Gain of 2.
The output of the Buffer Amp goes to the video input of your display via a 75 ohm resistor then 75 ohm coax.
The buffer amp can be made from an opamp with minimum of 4mA output and min of 10MHz band width.
The video input to the + input on the opamp, two 400 ohm resistors one between 0 volts and -input on opamp, the other between -input of opamp and opamp output (this sets up a gain of 2).




>>> .....sbwebb0spamspamspamBeGoneSAC.UKY.EDU 01/29 3:18 PM >>>
> Interesting but not anything particularly groundbreaking. From your reply I
> would infer that you are using two "standard" camera modules. If I am
> correct then I have to ask, How are you Genlocking them ?

Well, the module that I am woring with takes cares of that itself, I
guess.

1.  It supports an output mode where the two cameras are field interlaced
on one output, that is even fields come from camera 1, and odd fields from
camera 2.  This in itself suggests to me that it's genlocked internally.

2.  I put both signals on my [very crappy] scope, and found the sync on
both of them.  They were synced pretty darned well (ie I couldn't visually
tell a time skew between the two on my [very crappy] scope)

-Steve

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