45
17.3 RF Sensor (Bridge) Adjustment
The amplifier is switched off for this adjustment.
Check if adjustment is required as per following procedure, before opening the sensor.
Unsolder and remove the metal cover.
Connect a transceiver to the input and a dummy load to the output of the amplifier.
Connect a voltmeter (+) to pin SW1 or SW2 on the control board (with yellow/black wires).
Apply 30-50W RF on 20m (14.2MHz) and read the voltage.
Move the voltmeter to pin SW3 or SW4 (red/black wires) and read the voltage.
Typical readings:
-
Yellow / black wires: 1.5 – 2.2 V
-
Yellow / red wires: 100mV or less (preferably <40 mV).
Adjust the trimmer on the output side (left hand side) in the RF sensor for minimum reading on the yellow / red wires.
(Use an RF screwdriver).
Reverse the 2 RF cables: apply power to the output of the amplifier and put the dummy load on the input.
Apply power again.
The typical readings are the same, but reversed:
-
Yellow / black wires: 100mV or less (preferably <40 mV).
-
Yellow / red wires: 1.5 – 2.2 V
Adjust the trimmer on the input side (right hand side) in the RF sensor for minimum reading on the yellow / black wires.
Re-position the RF sensor cover and solder.
NOTE:
the above voltages can be measured as explained above and if the readings are correct, no adjustment is
necessary (the sensors are pre-adjusted before being installed).
The adjustment is very stable and normally no readjustment is necessary. Some models of RF bridge don’t even have
trimmers, fixed capacitors have been used instead.
Figure
24
RF Bridge
INPUT
SIDE
TRIMMER
OUTPUT
SIDE
TRIMMER
No Adjustment