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TM-V708A
5
CIRCUIT DESCRIPTION
IF IC
IC100
IF AMP
X3
X2
AF
MCF
XF100
CF
12.8MHz
SINGLE BALANCED
MIXER
RF AMP
HPF
HPF
LPF
Q112
2SC5108
(Y)
Q102
2SC4649
(N.P)
Q200,201
2SK302
(GR)
Q7
2SC5108
(Y)
Q508
3SK239A
38.4MHz
ANT
Fig. 4 Sub VHF Receiver circuit
Fig. 5 Sub UHF Receiver circuit
2-3. Sub VHF Receiver
The signal distributed from the RF amplifier (Q205) at the
main VHF receiver circuit passes through a filter circuit. Then
it enters the RF amplifier (Q507). The amplified signal goes to
the single balanced mixer (Q501, Q502). The frequency of
the signal is converted by the first local oscillator generated
by half of the UHF VCO oscillator frequency, using the
prescaler (IC303). It convents to the upper heterodyne
frequency to generate a 45.05MHz first IF signal. The signal
passes through the MCF (XF400). Then it is amplified by the
IF amplifier (Q406), and enters the IF IC (IC400). The signal is
converted to the 455kHz second IF signal, using the second
local oscillator (Upper heterodyne). Then the signal is
detected to generate an audio signal.
2-4. Sub UHF Receiver
The signal distributed from the RF amplifier (Q508) at the
main UHF receiver circuit passes through a lifter circuit. Then
it enters the single balanced mixer (Q200, Q201). The signal
frequency is converted by the first local oscillator, generated
by doubling the VHF VCO oscillator frequency (Lower
heterodyne) by Q7, to generate a 38.85MHz first IF signal.
The signal passes through the MCF (XF100). Then it is
amplified by the IF amplifier (Q112), and enters the IF IC
(IC100). The signal is converted to the 450kHz second IF
signal by the second local oscillator generated by tripling the
12.8MHz reference oscillator frequency (Lower heterodyne).
Then the signal is detected to generate an audio signal.
IF AMP
MCF
XF400
HPF
SINGLE BALANCED
MIXER
LPF
RF AMP
LPF
Q406
2SC5108
(Y)
Q501,502
2SK302
(GR)
LO
RF AMP
Q507
3SK239A
1/2
IC303
UPB
1509GV
Q205
3SK239A
AF
45.505MHz
IF IC
IC400
CF
ANT