AL-800H Instruction Manual
16
ALC Controls
The position of the
"ALC SET"
control determines the grid current value that will begin to produce ALC
voltage. Rotating the
"ALC SET"
control counter-clockwise
reduces
the maximum grid current
obtainable and the available RF power output. Rotating the
"ALC SET"
control clockwise
increases
the
maximum grid current level.
The approximate grid current available before ALC action begins can be determined by placing the
"MULTIMETER"
switch in the
"ALC SET"
(far clockwise) position. The
"ALC SET"
control should
normally be adjusted to produce a multimeter reading of 3 to 6 volts with the
"MULTIMETER"
switch in
the
"ALC SET"
position. This will allow a maximum grid current of approximately 15 to 30 mA.
ALC Adjustments
During SSB operation,
two adjustments affect the ALC and the sound of the signal. One is the
exciter's
microphone gain (or RF output level) adjustment. It will control the "fullness" of the ALC and the average
output power. It will have very little effect on the peak output power, however. The fullness of ALC action
is indicated by the meter reading in the multimeter
"ALC"
position. More exciter audio gain or power
output will drive the amplifier's ALC circuit harder, and produce a more constant meter reading. This
produces RF compression that increases the "talk power" without increasing signal bandwidth or distortion.
Note: Audio background noise will increase while using heavy ALC levels on SSB. Objectionable
background noise levels may occur while using heavy amounts of ALC, especially if the heavy ALC levels
are used in conjunction with other speech processing. In these situations, operating in a quiet room and
"close talking" the microphone will minimize objectionable background noise.
The amplifier's
"ALC SET"
control determines the
level
of grid current that produces ALC activity. The
maximum power output level. This amplifier has the best linearity when the
"ALC SET"
control is
adjusted to limit the peak grid current to 40 mA or lower. This adjustment must be made with a carrier or
single tone signal. When the
"ALC SET"
control is properly adjusted, it will be impossible to exceed 40
mA of grid current with any tuning or drive adjustment.
During CW operation,
the
"ALC SET"
control voltage should be adjusted just high enough (clockwise)
to allow the desired output power to be reached. The
"ALC SET"
control should
never
be adjusted to the
point where the grid current can exceed 50 mA under any tuning or drive adjustment condition. During
proper CW ALC operation, the exciter drive level control should be adjusted until the ALC voltage meter
slightly flickers (ALC position of the
"MULTIMETER"
switch) while operating with normal output
power levels.
The ALC circuit will limit the amplifier's grid current to a safe value if anything accidentally changes in the
station or the antenna. The CW keying waveform of the radio will remain unaltered when the ALC is
adjusted in this manner.
Note: Caution should be exercised if the "ALC SET" is used to control the CW power output with
the exciter power control set at maximum. Key clicks may be produced if the exciter has a
poor ALC response time. Check for proper wave shape when using the ALC in the amplifier
exclusively to control the RF output power.
