Tait TB7100, Service Manual

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320 Transmitter Fault Finding (50W/40W) TB7100 Service Manual
© Tait Electronics Limited October 2005
14.4 RF Signal Path
Introduction
The RF signal path extends from the output of the frequency synthesizer to
the LPF. This section of circuitry will require investigation either following
certain checks in
“Transmitter RF Power” or if the biasing checks of
“Biasing of PA Driver and PAs” reveal no fault. The procedure is divided
into ten tasks grouped as follows:
■
Task 26 to Task 30 : initial RF signal path
■
Task 31 and Task 32 : directional coupler
■
Task 33 and Task 34 : PIN switch
■
Task 35 : LPF
The initial signal path includes the exciter and PA driver. The directional
coupler, PIN switch, and LPF make up the final signal path.
The measurement points for diagnosing faults in the signal path are
summarized in
Figure 14.20 .
Figure 14.20 Measurement points for diagnosing faults in the RF signal path
TEST
CAPACITOR
TEST
CAPACITOR
L314
RF CON-
NECTOR
RECEIVER
LPF
DIREC-
TIONAL
COUPLER
PAs
PIN
SWITCH
DRIVER EXCITER
FRE-
QUENCY
SYNTHE-
SIZER
SIGNAL TYPES
RF
ANALOG
SYNTHESIZER
OUTPUT
SYN TX LO
PA DRIVER
OUTPUT AT
DRAIN OF Q306
STAGE 2
OUTPUT
AT C3509
STAGE 1
OUTPUT
AT C3505
50 TEST
LEAD TO
TEST SET
W
50 TEST
LEAD TO
TEST SET
W
STAGE 3
EXCITER
OUTPUT
GATES OF
Q309, Q310
C307
C3500