LX Series Digital
Chapter 4, Circuit Descriptions
Power Amplifier Assembly
Volume 2, Rev. 1
4-6
There are two identical signal paths on
the board: one for forward power and
one for reflected power. A sample of
forward output power, from the external
DTV mask filter, enters the board at the
SMA jack J1. Resistors R1 and R2 form
an input impedance-matching network of
50
Ω
. The forward power signal is
detected by CR1, R7, R25, C1, and C7.
For digital operation the jumpers, W1 on
J6 and W3 on J8, are both between pins
1 & 2. The detected output is buffered
by the operational amplifier U1C before it
is split. One part is connected to the
forward uncalibrated power output jack
J4. The other split output is connected to
forward power adjust pot R9, which
adjusts the gain of U1D. The output of
U1D is split with one part connected to
J3-4 Forward Power Metering Output #1.
The other output of U1D is connected to
J3-6 Forward Power Metering Output #2.
A sample of reflected output power, from
the external DTV mask filter, enters the
board at the SMA jack J2. Resistors R3
and R4 form an input impedance-
matching network of 50
Ω
. The reflected
power signal is detected by CR2, R26,
R8, C3, and C8. For digital operation the
jumper W2 on J7 is between pins 1 & 2.
The detected output is buffered by the
operational amplifier U1B before it is split.
One part is connected to the reflected
uncalibrated power output jack J5. The
other split output is connected to reflected
power adjust pot R10, which adjusts the
gain of U1A. The output of U1A is split
with one part connected to J3-9 Reflected
Power Metering Output #3. The other
output of U1A is connected to J3-11
Reflected Power Metering Output #4.
The +12 VDC needed for the operation of
U1 on the board enters the board at J3-2
and is connected through a filter and
isolation circuit consisting of C5, C9 and L3
before it is connected to U1. The -12 VDC
needed for the operation of U1 on the
board enters the board at J3-8 and is
connected through a filter and isolation
circuit consisting of C6, C12 and L6 before
it is connected to U1.
This completes the circuit description of the
external power amplifier assembly and
external assemblies.
