Operating instructions

Amplifier Setup 3-11
Vertical Automatic Drive Unit/QAM Automatic Drive Unit
The VADU and VQADU operate by using surface acoustic wave (SAW) filters to select a pilot
frequency and then monitor 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 VADU
(Figure 3-5) and VQADU (Figure 3-6) maintain a more precise output level than leaving the
MBV3-100* in manual control.
Figure 3-5
ADU
Figure 3-6
QADU
To set-up the VADU/VQADU:
1 Position the drive control select jumper (Figure 2-11) 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 VADU or VQADU control unit is the same as the
system pilot frequency. For the VADU, the pilot frequency is a CW pilot or an available
NTSC television channel not scrambled using sync suppression and not a digital channel.
For the VQADU, the pilot signal is a VQAM modulated digital channel.
3 Position the drive control select jumper to DRIVE UNIT.
MBV3-100* Installation and Operation Manual