
LA1787M
? Separation adjustment (pin 19)
5 k ?
To the
subdecoder
Larger
19
A12094
20 k ?
0.047 μ F
C
A12093
Fig. 49
The separation is adjusted by modifying the input level to the subdecoder with the variable resistor connected to
pin 19. Since only the sub-modulation level is changed by changing the variable resistor setting, the monaural
(main) output level is not changed. Furthermore, degradation of high band separation in the decoder can be avoided
if the impedance of the external capacitor (C) in the subchannel frequency band (23 to 53 kHz) is made sufficiently
smaller than the variable resistor.
6. MRC Circuit
VCC
2 μ A
S-meter
FM
S-meter
DC buffer
MRC
100 ?
QMRC
6.4 k ?
3.6 k ?
10 k ?
75 pF 1 k ?
30 k ?
24
32
Noise amplifier
27
High-pass filter with
+
Fc = 70 kHz + amplifier
+
C27
VCC
An external transistor equivalent
to the 2SC536 is required
To the SNC, pin 28
Reason: A QMRC level shifter is
required to allow a simplified MRC
circuit to be used in the LA1787M.
A11768
Fig. 50
No. 6655-43/54