Crown FM150, User Manual

Page: 41 / 110

3.7 RF Output Control
Set this control for the desired output power level. Preferably, set the power with an external
RF wattmeter connected in the coaxial line to the antenna. You may also use the RF power
reading on the digital multimeter.
The control sets the RF output voltage. Actual RF output power varies as the approximate
square of the relative setting of the control. For example, a setting of “50” is approximately
1/4 full power.
3.8 Digital Multimeter
The four-digit numeric display in the center of the front panel provides information on trans-
mitter operation. Use the “Up” and “down” push-buttons to select one of the following pa-
rameters. A green LED indicates the one selected.
Illustration 3–5 Digital Multimeter
RF Power—Actually reads RF voltage squared, so the accuracy can be affected by VSWR
(RF voltage-to-current ratio). See section 5.4 for calibration. Requires calibration with the
RF reflectometer being used.
SWR—Direct reading of the antenna standing-wave ratio (the ratio of the desired load im-
pedance, 50 ohms, to actual load).
ALC—DC gain control bias used to regulate PA supply voltage. With the PA power supply
at full output voltage, ALC will read about 6.0 volts. When the RF output is being regulated
by the RF power control circuit, this voltage will be reduced, typically reading 4 to 5.5 volts.
The ALC voltage will be reduced during PA DC overcurrent, SWR, or LOCK fault conditions.
3-7 Operation