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A 0dBmV signal is the minimum amount allowed by the FCC (Federal Communi-
cations Commission). This will produce a good to moderate quality TV picture,
depending upon the specifications of the TV connected to the signal. Some TV’s
can provide good pictures with a -10dBmV signal.
A +10dBmV signal is a ‘hot’ signal, and should provide more than adequate
signal level to any TV and in some cases, may provide too much signal level,
resulting in ‘overload’ of the TV’s tuner. This won’t damage the TV, but it may
produce various interference patterns between different channels (channel bleed-
ing or ghosting), or cause distortion in the picture or sound.
A good signal that will work with almost all TV’s is in the +5 to +10dBmV range.
The distribution system for the TV signal should be designed to place the signal,
at all outlets, in this optimum range. If you are an experienced installer, and
know the typical levels that provide good picture to a TV, you may expand the +5
to +10dBmV range to a range that works well based on your experience. For
example, you may decide that a range of 0dBmV to +15dBmV is acceptable or
-10dBmV to +18dBmV is OK. The wider the acceptable range, the simpler the
system will be to implement. It is also important to know the typical signal level,
measured at the connection to the building, that is acceptable to your Cable TV
Provider. In many localities, it is in the +10dBmV to +15dBmV range.
9.8.2 How much Loss is acceptable?
If the Cable TV Provider typically delivers a +14dBmV signal to the premises,
and a minimum of +5dBmV is desired all outlets the maximum Loss is 9dB
(14dBmV - 9dB = 5dBmV). If the cable runs are relatively short, then a 6 way
splitter (see Figure 7) could be added to supply 6 outlets with a signal of ap-
proxi5dBmV. To test the system for the appropriate Loss, first calibrate
the CableRater Transmitter to the Receiver, then connect the Transmitter to the
splitter input and measure each outlet for Loss with the Receiver. The Loss should
measure about 9 or 10dB.
If a +3dBmV signal is acceptable at the outlets, and cable runs are short, an 8
way splitter can be used (+14dBmV - 11dB = 3dBmV). If cable runs are long,
and more outlets are needed, then an amplifier may be necessary.
9.8.3 How many TV’s are to be connected at once?
Many new houses have cable TV outlets in every room. It is not expected that
every room will have a TV, but it is not unusual for households to have 3 or more
TV’s. Outlets in every room allow the TV’s to be placed anywhere in the house-
hold without having to run new wires.
