Operating instructions

Amplifier Setup 3-15
MB*/* Installation and Operation Manual
Automatic Drive Unit
The ADU operates by using surface acoustic wave (SAW) filters to select a pilot frequency and
then monitors the amplitude of this frequency. Any change in signal level is fed back to the Bode
equalizer. It is assumed that the encountered signal level changes are due to changes in cable
attenuation and hybrid output associated with a change in temperature. The Bode equalizer
then changes its insertion loss to maintain a constant output level. The ADU (illustrated in
Figure 3-10) maintains the most precise output level of the three available methods.
Figure 3-10
ADU
A
UTOMATIC
DRIVE UNIT
ADU/ _______________
Pilot frequency
To set-up the ADU:
1 Position the drive control select jumper (Figure 2-15) temporarily to the MAN position and
perform the complete procedure described in Manual Gain Control if not already completed.
2 Verify that the frequency stamped on the ADU control unit is the same as the system pilot
frequency. The pilot frequency is a CW pilot or an available NTSC television channel not
scrambled using sync suppression.
3 Position the drive control select jumper to DRIVE UNIT.
4 Connect a signal-level meter to the FWD OUT test point and tune the meter to the high
band-edge carrier.
5 Turn the auto level (ADU) potentiometer (illustrated in Figure 2-15) fully clockwise and
then reduce to obtain the level obtained in Step 9 under Manual Gain Control.
ADU Pads and Levels
This ADU subsection provides information regarding the proper ADU padding requirements for
the MB*/*.
A JXP-*B pad is installed in the input line to the ADU location. This pad adjusts the ADU input
level for the standard application of the MB*/* but can be changed depending on the operational
output. In general, a JXP-14B pad is recommended in the MB*/* ADU circuit. This is the
standard pad value shipped from the manufacturing facility and is appropriate for an amplifier
output level range from +42 dBmV to +50 dBmV at 550 MHz.
Motorola does not recommend operating at levels above 52 dBmV.