User's Manual
VHF UNIDIRECTIONAL AMPLIFIER TECHNICAL MANUAL
9
The PA unit does have an input power detector. If more than +3dBm is detected at the input port, the
PA drain voltage will be turned off, and the ALM red LED will turn ON. In order to bring the PA back
to its normal operation state, the operator should decrease the PA input power at least 10dB, then reset
the main power supply if necessary, and re-adjust the PA input power again to the desired level.
The PA output port is not well matched to 50 ohms (~ -13dB return loss). An isolator for connecting
the PA output to a filter or diplexer is required.
THE VGA AND PA SHOULDN’T BE TURNED ON IF THEIR OUTPUT PORTS ARE NOT
TERMINATED INTO A 50 OHMS LOAD.
Visual Interface LEDs
The VGA has 4 visual interface LEDs: two for the biasing voltage status and two for the optimum input
power level adjustment.
The PA has 4 visual interface LEDs: two for the biasing voltage status and two (working in Exclusive
OR logic) indicating quality of the PA output connection.
Table III: LED description
Location LEDname Designation Description Color
VGAUnit +5V_B D1A ON=the+5V_BispresentintheVGA Green
VGAUnit +5V_A D1B ON=the+5V_AispresentintheVGA Green
VGAUnit P_INLO D2A
ON=theinputpowerislowerthanorequal
tothedesiredlevel Green
VGAUnit P_INHI D2B
ON=theinputpowerishigherthanorequal
tothedesiredlevel Green
PAUnit +5_PA D5A ON=the+5Varepresents inthePAsection Green
PAUnit +48V_PA D5B ON=the+52VispresentinthePAsection Green
PAUnit PA_IN_PWR
D6A
D6B
GreenLEDON=theoutpowerislowerthan
33dBm.PAatnormalbiasing.
Green
or
Red
RedLEDON=thePAisturnedoff
(inputpowertoohighsuchthatthePA
outputpowercanbegreaterthan+33dBm).