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4. Transmitter PLL
The output signal from VCO
Q9:
2SK241(GR)-1
is
buffered by Q10 and Q11:
2SC2668(Y) and is output as
the TXO signal (transmit frequency).
A part of this signal
from Q10 is coupled through buffer Q13:
2SC2668(Y) to
mixer Q14:
2SC2668(Y).
A part of the RXO output fed
from the common
PLL is also supplied through isolation
amp 04:
2SC2668(Y) to mixer Q14: 2SC2668(Y).
The
mixer output (21.4 MHz) is amplified by Q15, divided by
TK-701
PLL IC U19:
MC145151
and coupled to the phase detec-
tor. The 21.4 MHz OFFSET (and modulator) oscillator out-
put is also divided by U19 and coupled to the phase detec-
tor.
The output of the phase detector is supplied to the
loop filter and then to varicap diode D3:
152208 as the
VCO control voltage.
RA20~
26
RA | of
12x 8 ROM
Reference
Decoder
OSCout O<2~»
RA 002-4
tittpepetereet
OSCin 27
+2
be
12 Bit+R Counter
Oot ror L 28 Ki
Vop 03
Vss
Of
i|
Phase
4
_.
Detector
-——OPD out
t
Fin
_|
a.
Phase
-—2o6v
ot +—lSo
14 Bit=N
Counter
-—?
Detector
|
856R
PEEEEEPEPEEEE
ES
lOsry
Transmit 2!
Receive
Transmit Offset Address
FOPRROREREREEE
7
5
311
1
Nia.
Nil
NS
7N6
N@4
N2
NO
Fig. 4-12 MC145151P
(PLL unit U19)
4-7
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