Blonder tongue AMM-806, Reference Manual

Page: 186 / 285

179
Ghosts
Ghosts are duplicates of the reproduced picture located to the right
or left of the picture. Ghosts displaced to the left are generally due
to ingress, for example, direct pick up. Assuming ghosts are not
present in the signals at the headend, ghosts displaced to the right
are generally indicative of impedance mismatches in the system,
for example, devices with poor return loss.
The following will help to find the
cause of a ghost that is displaced
to the right.
d
D
25845 = constant derived from speed of light x scan time for
horizontal line
X = distance in feet between the source of reflection and re-reflection
d = displacement of ghost on TV set in inches
D = horizontal width of TV set in inches
Vp = Velocity of Propagation referenced to free air
Example:
TV screen, D = 24 inches wide
Ghost image, d = 0.16 inches wide
Velocity of propagation for cable, Vp = 0.88
X = (25845 ft) x (0.16 in) x (0.88)
= 152 ft between devices
24 in
.
Once distance X is calculated, check the system maps for both (1)
the circumstance
where there are devices that are approximately
distance X apart and (2) that
the circumstance
is between to the
signal source and the location where the ghost is being viewed.