TS-990S
29
CIRCUIT DESCRIPTION
Fig. 30 From the IF input stage to the SCIF (3rd IF)
SC08M
ATT: 0dB
SC11S
SC73S
PLL
DDS
SCREF
ATT: -10dB
ATT: -20dB
ATT: -30dB
ATT
ATT
ATT
ATT
PLL
DDS
MCF
DDS
SFIC
6-4. From the IF Amplifi er (SCIF2_AMP) to the 3rd
Mixer (SCMIX3) Output
In the 3rd mixer (SCMIX3), the signal is down converted
by the SCLO3, and converted to the 3rd IF (SCIF3: 24kHz).
6-5. From the 3rd Mixer (SCMIX3) to the SCIF
The 3rd IF (SCIF3: 24kHz) is amplifi ed by the OP ampli-
fi er (IC9) and sent to the control unit (X53-452) as SCIF.
6-6. SCREF
The scope unit has equipped two PLL and three DDS,
and it receives a 40MHz reference signal as SCREF from
the PLL (MAIN) unit (X50-322) in order to distribute approxi-
mately 8.4MHz reference signal to PLL (IC4, IC6) through
DDS (IC1, IC2).
After this 40MHz reference signal passes buffer amplifi er,
it is distributed to three DDS as master clock.
Approximately 8.4MHz reference signal generated
by DDS is inputted into each PLL of SCLO1 and SCLO2
through a ceramic fi lter. The signal for SCLO3 use is con-
verted into 10.676MHz by the DDS and becomes the
SCLO3 signal via the amplifi er and fi lter.
6-7. PLL to SCLO1/SCLO2
■
SCLO1
The VCO consists of components including the induc-
tor (L60) and variable capacitance diode (D15). The PLL
(IC4) is in control of this VCO for the SCLO1 use. The VCO
outputs different oscillation frequencies (64.847MHz and
61.721MHz) for main signal reception and sub signal recep-
tion.
■
SCLO2
The VCO consists of components including the inductor
(L85) and variable capacitance diode (D23). The PLL (IC6)
is in control of this VCO for the SCLO2 use. This oscillation
frequency (83.795MHz) is changed by ±250kHz to perform
scope sweeping. It is performed every 10kHz by dividing the
bandwidth.
Fig. 31 MCF adjustment
L79
XF1L75
CN10
From 1st Mixer
10.7MHz
Tune connector
CN12
To 3rd Mixer
Tune connector
Q44,45
Supply 8V
6-3. MCF Adjustment
The MCF (XF1) is prepared for the 2nd IF frequency
(10.7MHz). Since the MCF terminal impedance is 1 k
, the
impedance is converted using variable inductors. The MCF
is a filter that consists of a 2-pole MCF with a center fre-
quency of 10.7MHz and a passband width of 15kHz.
Connect an appropriate device, such as a tracking gen-
erator, to the MCF adjustment connectors (CN10 and CN12)
and turn the variable inductors to adjust the MCF. Make the
MCF adjustments while in adjustment mode if you have
replaced the MCF (XF1), variable inductors, or scope unit
(X42-343 A/10). When adjusting the MCF, apply 8 V (8 A) to
the scope unit.
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