Kramer Electronics VP-61xl - Manual (Page 5)

KRAMER ELECTRONICS LTD. 4
cable is replaced by five individual coax cables, which are bulky and
cumbersome for use. Even then, the distance is limited to several tens of meters.
The imperfect behavior of a cable may create other problems resulting from its
failure to accurately match the system’s required impedance. The result of this,
especially at high frequencies, is “shadows” or “ghosts” on the image, resulting
from standing waves and electronic reflections running back and forth between
transmitter and receiver. Another aspect to consider is the sync. As sync signals
are logic signals, which are not treated as analog signals, the receiver does not
terminate the line, and therefore the line is not matched. A host of problems can
occur when sync signals are sent over long, unterminated, unmatched cables. The
result might be image breakdown or distortion due to improper sync information.
The amplifier that drives the analog section of the graphics data should also be
able to buffer, recover and send the sync information in such a way that it is
received properly at the receiving end.
1.3 Factors Affecting Quality of Results
There are many factors affecting the quality of results when signals are
transmitted from a source to an acceptor:
Connection cables - Low quality cables are susceptible to interference;
they degrade signal quality due to poor matching and cause elevated noise
levels. They should be of the best quality.
Sockets and connectors of the sources and acceptors - So often
ignored, they should be of highest quality, since "Zero Ohm" connection
resistance is the target. Sockets and connectors must also match the
required impedance (75ohm in video). Cheap, low quality connectors tend
to rust, thus causing breaks in the signal path.
Amplifying circuitry - Must provide quality performance when the
desired end result is high linearity, low distortion and low noise operation.
Distance between sources and acceptors - Plays a major role in the final
result. For long distances of over 15 meters (~2 to 3 meters for
VGA/XGA) between sources and acceptors, special measures should be
taken in order to avoid cable losses. These include using higher quality
cables or adding line amplifiers.
Interference from neighboring electrical appliances - They can have
an adverse effect on signal quality. Balanced audio lines are less prone to
interference, but unbalanced audio should be installed far from any mains
power cables, electric motors, transmitters, etc. even when the cables are
shielded.