Power Line Carrier ____________________________________________________________________
RF-MCGARDPRO
Hubbell Power Systems, Inc.
–
RFL™
Products
July 1, 2022
©2022 Hubbell Incorporated
5-38
CA
UT
IO
N
S
T
A
T
IC
S
E
N
S
IT
IV
E
R1
3
A
M
P
IM
P
E
D
A
DJ
R8
A
M
P
G
A
IN
A
DJ
R1
9
T
X
F
A
IL
A
DJ
P
A
OUT
R
X
IN
FI
N
E
C
O
A
R
S
E
TX
/R
X
2
W
TX
4W
RX
GND
+
1
5
V
-1
5
V
G
N
D
C
L
I
Connect dummy load
Common test point (black)
RX in test point
(yellow)
Power amp out test
point (red)
Common test point (black)
R13 Amp impedance adjust
R19 Amp TX fail adjust
R8 Amp gain adjust
R46
S1
Figure 5-19. PLC Rear Module Adjustments
Verifying/Adjusting Amplifier Output Impedance
Perform the fine adjustments to precisely match
impedance and minimize the reflected power.
The HPS/RFL GARD Pro system PLC amplifier output impedance is factory-set for 50-ohm
impedance.
When the load and source impedance are precisely matched, the loaded output voltage is exactly
one-half of the unloaded output voltage (or, the loaded output is 6dB below the unloaded output).
This fact is used to fine-tune the output impedance of the PLC amplifier.
Proceed with the following steps.
1.
Remove the rear PLC board and find jumpers J35/J36. See
locations of the jumpers. 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”.
