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(at 100 feet) must be considered if the Provider has channels reaching up to 100
or more. The difference between the 60MHz and 900MHz levels is called ‘tilt’. In
this case, the tilt is about 8dB in 100ft of RG-59. 50ft of RG-59 would exhibit
about 4dB of tilt.
It is not unusual for the Cable TV Provider to have already introduced tilt com-
pensation to the TV signals. That is, the higher frequencies (channels) will al-
ready be adjusted higher in level when delivered to the customer premises. A tilt
of +4dB is typical.. which would compensate for about 50ft of coax. If one con-
siders the AGC circuit (Automatic Gain Control) in all modern TV appliances, the
tilt of an additional 50ft of coax is automatically compensated for. So, depending
on the signal coming from the Provider, it may not be necessary to introduce
any special compensation on up to 100ft of coax... even on a 100 or 150 channel
system.
Systems with a lower number of channels, like 78 or 80 channel systems, often
don’t require special compensation until the coax is longer than 200ft.
If tilt compensation is required, an in-line tilt compensator or an amplifier with a
tilt adjustment can be used. Use the instructions provided with the compensator
for proper use and adjustment.
9.9 Identifying Cables
When a large number of cables have been installed and are unmarked, the
CableRater can aid in identifying the cables. The typical distribution system lay-
out has the ends of all of the cables routed to a central location, and the far ends
of these cables located in the areas where televisions will be connected.
Calibrate the Transmitter as described in 9.4. Estimate the length of cable to be
tested and estimate its loss. For example, a 100 foot cable will have about 2 or
3dB of Loss (see Figure 6). Turn on the Transmitter and connect it to the TV end
of the cable. At the central location, turn on the Receiver and experimentally
connect it to various cable ends. All of the cables, except the one with the Trans-
mitter signal, should measure Underrange.
The measured signal from the Transmitter should show the loss of the cable. If
the loss is higher than the amount attributable to the estimate of cable length,
then there may be a splitter or other device inserted somewhere in the cable... or
the cable may be faulty. If there is a splitter in the cable, then the Transmitter’s
signal may appear on more than one cable. Once you believe you have identified
the cable, turn off the Transmitter and verify that the Receiver reads Underrange.
If you obtain unexpected readings on the Receiver, you may be seeing the ef-
fects of Ingress. See section 9.3.
