User's Manual

Automatic Level Control Circuitry
A voltage controlled attenuator placed after the frequency response equalization circuit
allows dynamic adjustment of the IF signal gain and provides a means of controlling the
level of output power generated by the power amplification stages of the system.
The voltage to the attenuator can be monitored externally through the DIN connection J1-
11C ALC VOLTAGE. If the attenuator voltage exceeds 8V the Red ALC FAULT LED on the
front of the module will illuminate. If this occurs the ALC has reached the end of its operat
ing range and will no longer maintain the proper output power level.
Certain conditions will also place the ALC in a mute state. In this condition the attenuator
voltage is reduced to zero and the level of output is extremely low. A red LED labeled MUTE
on the front of the module indicates this condition. The mute status can also be monitored
externally through DIN connector J1-9 which is set to logic low when the ALC circuit is in a
mute state, however when operating in manual mode the mute condition will be overidden.
Various conditions are described in the table below.
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Mode Operation
Manual - the attenuator gain is controlled manually by The voltage to the attenuator can be adjusted directly by
selecting the manual mode of operation with the toggle the manual gain poteniometer R149 on the front of the module
switch SW2 on the front of the module
ALC - the output power of the system is controlled The desired level of output power can be adjusted from the
automatically by selecting the ALC mode of operation fron of the module by the ALC potentiometer R139. The ALC
with the toggle switch SW2 on the front of the module. circuit will automatically adjust the voltage to the attenuator in
order to maintain the desired output power.
Condition Action
The input signal detection circuitry senses an input fault. The ALC will be forced into the mute state to prevent
transmission of noise.
The input signal detection circuitry senses a peak vs The ALC will be forced into the mute state to prevent
average fault overloading the final transit path and the antenna.
An external device is commanding the ALC circuit to There is an external mute signal that can be applied to the
be placed in the mute state. module through DIN connector J1-10C MUTE I/P. Pulling this
connection to ground will force the ALC circuit to the mute
state.