User Manual AC1000
59300001 Rev.003
Broadband Cable Networks December 17, 2002 3(11)
printed on December 17, 2002
Adjustments
Forward path
The AC1000 is available in many configurations to fill various network
requirements. The amplifier is delivered according to the specifications defined
in the ordering code. Optional return path operation needs plug-in diplex filters.
The available diplex filter types are CXF030 (30/47 MHz), CXF042 (42/54 MHz),
CXF050 (50/70 MHz) and CXF065 (65/85 MHz). It is also possible to order the
amplifier with no diplexers, in which case the diplex filters are replaced by
forward path jumpers CXF000. In addition an optional element management
transponder module is available allowing remote monitoring and controlling of
the amplifier.
The input and output amplifier stages are both based on high performance
solutions which allows the operator to set this amplifier’s outputs for trunk or
distribution levels. Input and output modules are passive plug-ins used to
control the outputs – see table 1. During the adjustment the plug-in unit
positions for input and output modules must be equipped at least with the 0 dB
modules.
Install the interstage equaliser and attenuator plug-ins (fig.3 pos.14 and 13)
according the network plan. The network plan should specify exact signal
values.
Set the output slope of the amplifier according to the network plan calculation by
means of input equaliser (fig.3 pos.11). The signal can be measured at the
-20 dB output test point (fig.3 pos.7). To reach finally the desired output level
select an appropriate input attenuator for the plug-in position 10 (fig.3). Note! If
the income level of the amplifier is quite high or unknown, replace the input
attenuator in position 10 (fig.3) with an attenuator of rather big attenuation value
e.g. JDA915 (15 dB, 860 MHz).
Return path
The return path adjustment is based on unity gain principle such that the return
path gain of the amplifier station exactly matches the loss of the cable following
it (i.e., the cable span toward the headend). Inject a signal of known power into
the test signal injection point (fig.3 pos.6) in the amplifier and measure the
output level in the headend. Once the signal is received at the headend, it can
be measured and the information sent into the forward path as a narrowband
signal. This signal can be detected from the -20 dB test point (fig.3 pos. 7).
Adjust the gain (fig.3 pos. 18) and slope (fig.3 pos.17) of the amplifier until the
target level is produced.
The return path requires a specific signal level for proper operation. The ideal
level at the amplifier is based on the incoming power and the maximum loss
through which that signal must travel on its way to the amplifier. A typical
individual channel level at the return path input is in range of 70…80 dBµV.
Usually the return path input attenuator (fig.3 pos.16) is set to 0 dB. If the
amplifier is used as the last amplifier in a network and it is followed with a
distribution network with an exceptional low attenuation, an extra attenuation
can be added. Attenuators of the JDA series type ranging from 0 dB to 20 dB in
1 dB steps are available.
If the return path is not in use, the return path attenuator (fig.3 pos.18) should
be removed. The termination towards the headend will then be completed
automatically. Alternatively the return path can be terminated towards
