Kramer Electronics VM-1042 - Manual (Page 18)

KRAMER ELECTRONICS LTD.
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line (of 75 impedance) from first to last amplifier. Note that if looping function is not
used, the termination switch should be set to "75 ".
Level Control
(VM-1010, VM-1015, VM-1021, VM-54 only)
Level Control function enables the operator to control video signal level or compensate for
distortions such as those caused by cables that are too long. Using a non-standard, or an
uncalibrated video source also affects the incoming signal. Picture darkness is usually
caused by low video signal and on the other hand, excessive video level "burns" the
picture. The sync signal (approx. -0.3v) may be used to check conformity of the whole
video signal: If sync level is too low or too high, the incoming video signal is not within
the standard level. To correct the incoming video signal, an oscilloscope should be
connected to amplifier’ s output and the LEVEL trimmer adjusted until satisfactory sync
level and hence proper picture are achieved.
WARNING !
1. Be aware that the amplifier was pre-calibrated for
transparent operation at the factory and re-tuning
it will upset signal transparency.
2. Do not attempt to adjust the LEVEL trimmers
without using accompanying standard calibrated
oscilloscope or waveform monitor!
Equalization Control
(VM-1010, VM-1015, VM-1021, VM-54 only)
Equalization Control function enables the operator to compensate for degradation of the
video signal due to too long or non-standard cables. Popular cables such as the RG-59,
RG-11 or the RG-179 signal cause degradation/attenuation of the following values:
CABLE TYPE LENGTH FREQUENCY ATTENUATION
RG-59 100 meter
100 meter
10MHz
100MHz
3.6dB
11dB
RG-11 100 meter
100 meter
10MHz
100MHz
2.2dB
7.5dB
RG-179 100 meter
100 meter
10MHz
100MHz
8dB
30dB
Degradation and loss of video signal are mainly caused due to stray capacitance which
occur in long cables. As longer cables or higher frequency are used, the problem becomes
worse, resulting in fine detail loss as well as color degradation. When RGB signals are
involved (200-300MHz), degradation is even greater, leading to a total loss of sharpness at
high resolution. It is necessary to compensate for the problem by using the amplifier’ s EQ.
Control trimmer. Equalization is performed as follows: A Color Bar Generator is
connected to amplifier’ s input and a Waveform Monitor (or an Oscilloscope with 75
termination) is connected to the long cable output. A known color bar signal is applied to
the amplifier’ s input and compared to the signal monitored at the far side. The operator
adjusts the EQ. trimmer until the measured output chrominance signal matches that of the
input signal.