Installation and Commissioning
GARD 8000 SYS RFL Electronics
November 28, 2017 4-47 973.334.3100
4.6.3.1.3 OUTPUT IMPEDANCE
Once the GARD 8000 PLC has been connected to the line the output impedance should be adjusted to
match that of the actual line. Impedance mismatches can cause signal reflections and other undesirable
effects. The GARD 8000 PLC Power Amplifier provides an output impedance adjustment to
accommodate small variations in actual line conditions. When the load and source impedance of a
device are matched, the loaded output voltage is exactly one half of the unloaded output voltage (the
internal and external impedances form a 50% voltage divider). This fact is used to set the amplifiers
output impedance. However, the power amplifier is not able to supply twice the rated output voltage
when configured for 10 W operation. (The output impedance is simulated by active circuits in the
GARD 8000 PLC and the output compliance voltage is limited.) For this reason, the adjustment must
be made at less than 10 W output power.
1. Remove the rear PLC board and find jumpers J35/J36. Set the jumpers to “TEST” and re-
insert the module.
2. Send a “Guard” signal (FSK) or “Block” (On-Off) at 1W.
Note: Set block level to 1W (On-Off), otherwise send 1W Guard (FSK)
3. Disconnect the load from the amplifier.
4. Set the frequency-selective voltmeter (FSVM) to the transmit frequency and measure the
transmit output level across the “PA-OUT” (red and black) test points on the rear PLC board.
Either record the value, or set the meter’s 0 dB reference to the currently measured value.
5. Re-connect the load, continuing to measure the transmit output level.
6. Adjust the potentiometer R13 on the rear of the amplifier module to achieve 50% of the
previously measured voltage, (or to achieve 6dB below the previously measured level).
7. Remove the rear PLC board and set jumpers J35/J36 to “NORM”.
4.6.3.1.4 POWER AMP TX FAIL THRESHOLD ADJUSTMENT
1. Connect the FSVM to the PA OUT Test Points on the Analog Module and tune the FSVM for
the TX frequency.
2. Send Guard (In FSK) or Block (On-Off) at 1W (30dBm).
3. Adjust R8 on the Power Amplifier (located on the rear of the chassis) until the desired TX
Fail Threshold is shown on the FSVM.
Note: RFL recommends setting the threshold to 1.5 dB below the Guard or Block Signal
level (28.5dBm).
4. Adjust the TX Fail Threshold pot (R19) of the Power Amplifier until the TX Fail Output
turns on.
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