12.4
RF Signal Path
Introduction
Figure 12.13 Measurement points for diagnosing faults in the RF signal path
SIGNAL TYPES
RF
ANALOG
TEST
CAPACITOR
W
50
TEST
LEAD TO
TEST SET
RECEIVER
TEST
CAPACITOR
W
50
TEST
LEAD TO
TEST SET
RF CON-
NECTOR
TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
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"
"Biasing of PA Driver and PAs"
into nine tasks grouped as follows:
Task 25
to
Task
28: initial RF signal path
■
Task 29
and
Task
■
Task 31
and
Task
■
Task
33: 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
PAs
L314
GATES OF
Q309, Q310
DIREC-
TIONAL
COUPLER
PIN
SWITCH
LPF
reveal no fault. The procedure is divided
30: directional coupler
32: PIN switch
12.13.
EXCITER
OUTPUT
DRIVER
PA DRIVER
OUTPUT AT
DRAIN OF Q306
Transmitter Fault Finding (25W)
or if the biasing checks of
SYNTHESIZER
OUTPUT
SYN TX LO
EXCITER
C301
C300
BUFFER
OUTPUT
AT C313
QUENCY
SYNTHE-
SIZER
FRE-
379