
LA1787M
? Notes on AM SD (pin 26) and the SD adjustment pin
SD and the IF buffer are operated by comparing the S-meter level (V24) and the 5 V reference voltage as shown in
figure 36.
S-meter
VCC
50 μ A
Comparator
+
–
AM IF
IF buff amp.
50 pF
55
24
23
26
100 k ?
100 k ?
0.47 μ F
51 k ?
0.022 μ F
5V
Fig. 36
Seek
IF buffer
5V
SD
A12085
Figure 37 shows the relationship between the AM SD, the IF count buffer, and the S-meter.
V24PIN
V55
Larger
values
of R55
S-meter
V26
Smaller values of R55
SD on
V23AC
OFF
IF buffer on
V23DC
5V
Pin 55: AM SD adjustment pin
0V
A11760
Fig. 37
No. 6655-39/54