Directional Coupler Test Points; Bode Equalization; Amplifier Level Control; Manual Gain Control - Motorola STARLINE SERIES Installation And Operation Manual

3-12 Amplifier Setup

Directional Coupler Test Points

Accurate 20 dB directional-coupler test points are available at the input and at the output of
the MB*/*. Because these test points are 75-ohm source impedance, they do not require special
test probes.
After the output hybrid, a second directional coupler provides signal to the optional ADU board.
This signal is used only when the ADU board is installed. It is not necessary to terminate this
port when the ADU is not installed.

Bode Equalization

The Bode board, which is an electronically controlled equalizer, receives its control input from
either the ADU or TDU control boards. The response of the Bode board compensates for cable
attenuation changes due to temperature. If necessary, you can control the Bode board manually
using the potentiometer labeled

Amplifier Level Control

Signal levels vary in a cable system primarily because cable attenuation changes with
temperature. Other components such as passives and amplifier hybrids are also affected by
temperature changes. To automatically compensate for these signal level fluctuations and
control output level, you must select the optional ADU or TDU. The use of the ADU or TDU is
recommended for improved output level stability.
When necessary and appropriate, you can also use manual gain control. The gain of the MB*/*
is then determined by the potentiometer marked

Manual Gain Control

To use manual gain control:
1
Verify that the electronics chassis is installed correctly.
2
Ensure that there is continuity in the forward path by installing the design-value forward
equalizer and design value input JXP-*B attenuator.
3
Ensure that the drive control select jumper is in the
4
Use a signal-level meter to measure the high band-edge carrier input level at the input test
point: 750 MHz = channel 116, 870 MHz = channel 136.
This carrier should be at standard analog level, non-scrambled.
5
Verify that the input level agrees with the design specification input.
If the level is different from design, adjust accordingly. For example: the design level is
19 dBmV at the highest frequency and the design pad value is JXP-3B. If the actual
measured level is 21 dBmV, then you must change the pad to a JXP-5B.
If the actual levels are significantly different from the design levels, it is recommended that
you investigate or consult system management before proceeding.
6
Connect the signal-level meter to the output test point and tune the meter to the high-end
channel.
7
Turn the manual gain reserve (
clockwise) and then reduce the output as noted in Table 3-3:
MB*/* Installation and Operation Manual
shown in Figure 3-5.
MANUAL LEVEL
on the electronics chassis cover.
MAN
) control (illustrated in Figure 3-5) to maximum (fully
MAN
position.
MAN