Instruction manual

AL-800 Instruction Manual
21
ALC SET
...
In this position the multimeter measures the approximate grid current that will produce
ALC activity. One zero must be added to the reading on the
"ACL / HV"
scale and the result
divided by 2 for this function.
For example: If the meter reads 15, add one zero (150) and divide by 2 (75). In this example ALC
action will begin at approximately 75 mA of grid current.
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 20 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 20 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 25 mA under any tuning or drive
adjustment condition. During proper CW ALC operation, the exciter drive level control should be