Nortel CMTS 1000 Install Manual page 45

Hardware Installation
The CM 100's automatic power adjust, initiated by a received UCD con-
taining the proper upstream channel characteristic, causes all CM 100
transmitters to hit the input of the RF-to-Fiber Transceiver, or the first
active amplifier, at the same level.
The automatic power adjustment range is 43 dB (+8 to +55 dBmV) for CM
100 16 QAM transmissions and 50 dB (+8 to +58 dBmV) for CM 100
QPSK transmissions.
The attenuation for the return (upstream) path at the headend determines
the value of the signal level at the input to the return channel amplifiers.
In forward path calculations, the key reference point is the output level of
the amplifier. For return path calculations, the input level to the first active
device becomes the key reference point. Once the level is known, by sys-
tem design, all return path losses and gains back to the headend and CMTS
1000 are accounted for.
The key for selecting the attenuation for the return path is knowing the
input level to the first active device.
The cable modems minimum output is +8 dBmV. The path loss from the
subscriber location to the first active device must be sufficient enough so
that a lower level is not required to reach the designed input level of the
first active device.
When this process is followed, the return path is optimized for the 43 dB
(16 QAM) or 50 dB (QPSK) of cable modem TX range. The path loss from
the subscriber to the first active device cannot exceed these ranges. If
exceeded, the cable modem transmitter would be at its maximum output
and not be able to reach the TX level required to provide optimum
performance.
302693-B Rev 00 2-9