Specifications

If the input video signal deviates from the established standards, the tip of
white clamp will change the relationships within the video signal according to how
much the video input level is off of the standard level.
The standard level expected by the fiber equipment is 140 I.R.E. units,
specifically 100 I.R.E. units of White (Luminance) and 40 I.R.E. units of Sync
Pulse (Synchronization Pulse). The manufactures of fiber equipment rely on this
standard and expect the video source to be correct in order to deliver the video
correctly.
The equipment manufactures will tell you that “what you put in is what you
get out” and this is true, but only if you put in exactly a 100/40 video signal, any
other signal will give you a "non-unity" altered signal output. The relationship
between the input and output will vary depending on the relationship between the
Luminance and the Sync signal input.
Example #1: If your input Luminance starts out as 130 I.R.E. units a 30%
increase over a normal level, and the Sync level is a normal 40 I.R.E., this ads up
to 170 I.R.E. units, the clamp will reduce the total signal to 140 I.R.E. units, this
will change the Luminance signal to 107 I.R.E. and the Sync signal to 33 I.R.E.
This condition reduces the Sync level and could produce picture rolling if the
condition gets worse.
Example #2: If your input Luminance is 70 I.R.E. units a 30% decrease from
normal video level and the Sync is 40 I.R.E. normal, equaling 110 I.R.E. The
clamping system will convert these levels to 89 I.R.E. units of Luminance and 51
I.R.E. units of Sync. This condition will produce a darker than expected video
image. The higher Sync level can cause synchronization problems as well.
As you can see both the Luminance and the Sync levels are altered by the
fiber system if the Luminance level is not an exact 100/40 = 140 I.R.E. level. This
is the reason that your video input level may vary from your output level when
traversing a fiber optic system. You can test this process and see it for your self.
In a fiber optic system, cap the camera so that the luminance level is zero. Then
measure the Sync level, it can be as high as 140 I.R.E. units depending on the
range of the AGC in the fiber receiver. The normal level of Sync is 40 I.R.E. units.
This black out effect can cause Sync Pulse overdrive in the DVR or monitor. This
effect can be seen as rolling or tearing of the picture at night when the picture is
extremely dark.
CCTV TRAINING MANUAL PAGE 27 OF 28