T Ransmitter - Standard Horizon GX1250SA Service Manual

2.2.7 W eather Alert
Refer to Figure 2-4.
A portion of the audio signal from pin 11 of QR60 is applied to
pin 3 of the tone decoder IC Q107. In order for Q107 to oper-
ate a weather channel needs to be present in the scan memory.
If the audio signal applied to pin 3 contains a proper frequency
(1050 Hz), pin 8 of Q107 becomes a low voltage (0 V), and
applies to pin 11 (WA DET) of microprocessor QL01. Micro-
processor QL01 determines the weather alert tone is con-
tained, and outputs a low voltage from pin 12 (WA BEEP) which
is applied to AF amplifier Q101. This causes a beep tone to be
emitted from internal speaker EG30.
WA DECODE IC
8
Q107
NJM567M
AMP
QUADRATURE
PHASE DETECTOR
3
AUDIO SIGNAL
Figure 2-4 W eather alert BPF/ comparator block diagram
11 QL01
MICROPROCESSOR
12
WEATHER ALERT BEEP
AF Volume RG02
AF amplifier Q101
QR60
11
2nd IF IC

2.3 T ransmitter

2.3.1 Microphone Amplifier
Refer to Figure 2-5.
When the push-to-talk (PTT) switch of the microphone is
pressed, pin 3 of JL01 (microphone connector) is pulled Lo (0
V). This is applied to pin 1 of microprocessor QL01. When this
happens, pin 3 of microprocessor QL01 (TX cont.) outputs a
Lo to the TX+B switch Q204 which turns it on and supplies to
the transmit circuits. The audio signal input from pin 1 of JL01
(microphone connector) is applied to the pre-emphasis circuit
comprising CM01 and RM01. The audio signal obtains the fre-
quency response of 6 dB / Oct. there. The audio signal passes
through the pre-emphasis circuit is applied to pin 2 of the MIC
amplifier QM02 (1/2). The amplified audio signal is output from
pin 1 of QM02 (1/2), and is applied to diode QM01 to allow
amplitude limit.
The limited signal is applied to pin 6 of low pass filter Amplifier
QM02 (2/2). It contains a low pass filter circuit that attenuates
audio signals higher than 3 kHz by 18 dB/Oct. The signal level
is adjusted by Deviation Adjustment RM12. And this is applied
to YY06 of VCO ZZ01 to modulate the VCO.
VCO circuit
Vcc
8
QM02
Mic Amp/ LPF
NJM4558(Y)
1
Figure 2-5 MIC AMP/ LPF block diagram
6
7
6 5
LIMITTER
QM01
DAN202U
2 3 4
PRE-EMPHASIS
MICROPHONE
RM01
NA01 AUDIO SIGNAL
CM01