Transmission Circuit; From The Transmission Signal To The Drive Output; Blanking Circuit - Kenwood TS-990S Service Manual

■ Blanking Circuit

The blanking circuit attenuates the IF signal by the signal
detected in the noise detection circuit and removes the pulse
noise.
The SBLNK is set to "H", Q483 is turned ON, and Q482
is turned OFF when pulse noise is detected in the noise
blanker. Diodes (D481 to D484) are then turned OFF and
the IF signal is attenuated.
+8V
Blanking ON : 4V
Blanking OFF : 1.6V
L490
D481
IF in
D482
Fig. 25 Blanking circuit

5. Transmission Circuit

5-1. From the Transmission Signal (TIF) to the
Drive output
The transmission signal (TIF) is divided by the analog
switcher (IC686) in the DSP unit (X53-453) in accordance
with whether it's in FM mode or a mode other than FM.
DAC
Drive
out
Fig. 26 From the transmission signal (TIF) to the drive output
CIRCUIT DESCRIPTION
L491
D483
IF out
D484
Blanking ON : 8V
Blanking OFF : 0V
SBLNK
Q482, 483
H : Blanking ON
L : Blanking OFF
DSP unit (X53-453) TX-RX unit (X57-827 A/2)
IC686
IC701
TIF
SLO3
FM
Q707
In FM mode, the transmission signal is switched by the
analog switcher (IC686), sent to the PLL (MAIN LO) unit
(X50-322), and the frequency is modulated in audio signals
into the 1st local oscillator (TLO1) signal. In modes other
than FM, the transmission signal is switched by the analog
switcher (IC686), sent to the TX-RX unit (X57-827 A/2) and
then input into the balanced mixer (IC701). The 24kHz TIF
signal and 3rd local oscillator signal (SLO3) are input into
this balanced mixer to generate the 10.695MHz IF signal.
The 10.695MHz transmission IF signal passes the IF fi lter
(XF482) with a bandwidth of 6kHz through the buffer (Q702),
and is amplifi ed by the IF amplifi er (Q703). The pin diodes
(D703 and D705) operate the variable attenuator by the cur-
rent control, and change the transmission IF signal gain. The
variable gain provides the TGC function which controls each
band's transmission gain.
The 10.695MHz transmission IF signal is converted to
73.095MHz by the mixer (D405 and D406). Signal attenu-
ation is made variable by the current that passes through
the pin diode (D707), and thus the level of the 73.095MHz
transmission IF signal varies. The level control corrects the
transmission signal gain (PGC function) at the time of power
control. By varying the level of the transmission signal, cor-
rection of the gain at the time of power control can be per-
formed.
The transmission signal passing through the MCF (XF401)
with a bandwidth of 15kHz is converted to the target trans-
mission frequency in the final transmission mixer (IC702).
The MCF (XF401) helps reduce proximate spurious com-
ponents. The 73.095MHz IF signal is applied to the 1st gate
of the transmission IF amplifi er (Q706) for ALC control, and
the ALC voltage is in the 2nd gate control to make gain ad-
justments. The signal from the fi nal transmit mixer passes
through the receive BPF, and is amplifi ed to the power need-
ed to drive the fi nal stage in the drive amplifi er (Q707).
Q703
D703,705
10.695MHz
XF482
FM
IC702
Q706
XF401
TLO1 ALC
TS-990S
D405,406
SLO2
73.095MHz
D707
25