AL-800H Instruction Manual
17
Rear-Panel "ALC LIMIT" Control
The
"ALC Limit"
control (rear panel) limits the maximum voltage available from the ALC circuit. This
control is necessary only because the ALC response times and voltage requirements for exciters have never
been standardized. The ALC voltage requirements may even vary between different models produced by
the same manufacturer.
If the ALC response time of the exciter (transceiver) is faster than the rise time of the RF envelope, there
will be no voltage compatibility problems. The ALC voltage from this amplifier will automatically adjust
to the limit required by the exciter.
If the ALC voltage requirements are low and if the ALC attack time is slow, the ALC may cause the output
power to "pump" at a very slow rate. The undesired "pumping" can be corrected by reducing the amplifier's
ALC output voltage with the
"ALC Limit"
control (R1).
A full counter-clockwise
"ALC Limit"
setting will produce approximately 10 volts of maximum negative
ALC voltage. A full clockwise setting (viewed from amplifier rear) will produce no ALC voltage. Always
start with this control fully counter-clockwise before slowly advancing this control clockwise. The ALC
LIMIT ADJUSTMENT
section that follows gives adjustment details.
An external 1,000 to 5,000 ohm potentiometer can be added from the ALC output line to ground if the
particular amplifier you are using does not have a rear panel
"ALC Limit"
control. The chassis (shield) of
the amplifier's ALC output jack must connect to the clockwise (shaft end view) terminal of the ALC exciter
voltage control. The ALC jack center pin on the amplifier must connect to the counter-clockwise terminal
(shaft end view) of the external control. The center of the control connects to the ALC input of the exciter.
ALC Limit Adjustment (rear panel)
This adjustment procedure should be used if "pumping" occurs from excessive transceiver ALC sensitivity
and/or slow transceiver ALC response time:
1.
Load the amplifier for maximum output on any band (see tuning instructions later in this manual).
2.
Adjust the
"ALC SET"
control on the front panel and the rear panel
"ALC Limit"
potentiometer to
their full
counter-clockwise positions.
3.
Apply full exciter drive power, and adjust the rear panel
"ALC Limit"
potentiometer clockwise (rear
view) until the amplifier's ALC output voltage meter (multimeter
"ALC"
position) indicates 6 to 10
volts. As an alternative, the potentiometer can be adjusted clockwise until the RF output power
reaches 300-500 watts.
