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This filter is sensitive to the video sync pulses of TV signals. If the tone and bar graph do not change when the video filter is
switched on, this indicates that the measured signal contains these sync pulses and is a TV signal. If the tone and bar graph disappear
when the video filter is activated, the measured signal does not contain sync pulses and therefore is not a TV signal. This does not
guarantee that there is no leak of the CATV system. It is possible for there to be both video and non-video signals present at the same
time. If the non-video signal is larger that the CATV leak, it will mask the detection of the leak, just as a large CATV leak masks the
detection of smaller leaks.
Peak Level Indicator
press F2 to reset
Active Search Level
Search Mode - from a Vehicle
The DisplayMax can be used for patrolling your CATV plant to locate leaks and meet FCC ride out requirements. However, once a
leak has been located, measurements must be made from outside the vehicle. Instructions for calibrated leakage measurement can be
found in the next section of this manual.
However, the first task it locate a leak. For rough location purposes, you may use a
roof mounted monopole or dipole antenna.
Roof mounted dipole antennas
should be oriented in the direction of travel. Care should be taken to not catch overhead trees.
Dipoles should be positioned as close to the cable as possible (passenger side of the roof).
Roof mounted monopole antennas
should be mounted in the center of the roof as long as there are no other conductors which would
effect its performance. If your vehicle is equipped with roof mounted ladder racks, or a bucket, you may want to experiment using a
known leak to find the optimal position for the monopole.
Signal leaks are often hard to locate. Rain and wet ground, temperature changes, and wind can all effect the level of leaks. Leaks
may be active one day, and gone the next. Generally, RF leaks will follow the path of lowest resistance. This can be through space,
or along strand, telephone or power lines.
Signal leaks propagate in waves. These waves create patterns of rising and falling leakage radiation along the cable. A single leak
can therefore appear as a series of leaks as you drive parallel to the cable. Most leaks will be greatest near their source. One way to
find the source is to slowly travel along the cable while monitoring the rising and falling pitch of the DisplayMax. The peak hold
function of the display will also help you identify the location where the leak is strongest.
Conversely, what may seem to be one large leak, may be the composite signal of many leaks. It is vital to locate the largest leak,
repair it, and then search again for other smaller leaks that may have been masked by the large one.
Pinpointing the exact source of a leak can be difficult. Once in the general area of a suspected leak, it is often best to leave the vehicle
and follow the techniques for hand-held searching. Triangulation, using a hand held dipole antenna , is often effective.
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