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CHAPTER ELEVEN: T
Antenna Systems Interference
There are times when despite all the careful planning
and attention you've given an installation, outside
interference still shows up on the TV screen. Some of
the most common interference problems and their
solutions are discussed in this chapter.
GHOSTING
Ghosting is the appearance of faint duplicate images
alongside the true picture. Ghosting is caused by two
sets of the same signal arriving at the receiver at
slightly different times. Leading ghosts (Figure 11-1)
appear to the left of the main images. Trailing ghosts
(Figure 11-2) appear to the right.
Fig. 11-1. Leading ghosts appear to the left of the main images.
Leading Ghosts
Leading ghosts are caused by signals arriving at the
receiver a split-second ahead of the direct (primary)
signal. They are usually caused by direct pick up (pick
up other than the antenna).
Solution: Take great care with shielding and downlead
splices, etc. and if ghosting is still present, reorient the
antenna to minimize ghosts.
Fig. 11-2. Trailing ghosts appear to the right of the main images.
T
ROUBLESHOOTING
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ROUBLESHOOTING
Trailing Ghosts
Trailing ghosts are usually caused by TV signals that
bounce off hills or tall buildings. Because these
signals take a longer path to the antenna, they show
up on the screen a fraction of a second later than the
primary signal. Trailing ghosts also can be caused by
shorted-out or otherwise defective connections that
produce signal mismatch. This type of ghosting also
shows up in a distribution system when signals are
reflected back through the system by an unterminated
output terminal.
Solution: Use terminators on all unused distribution
terminals. Use a highly directive antenna (like a
Channel Master QUANTUM
reflected signals. Reorient the existing antenna; slight
reorientation often will eliminate the ghosting. As a
last resort try a special "ghost killer" antenna.
Smeared or Blurred Pictures
Blurred or smeared pictures (Figure 11-3) are
frequently caused by mismatched impedances or
improper connections in the transmission line or
other equipment.
Solution: Check all connections to ensure that they
are tight and not rusted or corroded. Check for and
eliminate any crimps or kinks in the downlead. Be
sure that the line has not been crushed by staples
and is not bent too sharply. Use only the best quality
coaxial cable, hardware, and other equipment to
ensure good impedance matching.
Fig. 11-3. Blurred and smeared TV pictures.
®
) that will not pick up
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