Squelch threshold is controlled by Resistor R18,C31,R15
f) Audio Amplifier
Demodulated audio signal enters to pin2 of U4. After above signal is amplified
in U4 the audio output for the speaker is reached at pin 5 (through C220).
5.3 Transmitter
When Tx starts with pressing PTT switch, VCO output amplifies through
Q4,Q5 transmits by antenna through low pass filter.
Tx RF signal produced from Tx VCO is amplified by DRIVER Q5 through C53
and entered Q4 POWER TR input terminal with final amplification.
After this stage, the signal is emitted at antenna through 50 Ohms matching
circuit to low pass filter(L7,L6,L5,C42,C43,C44,C46,C47) to eliminate
harmonics.
5.3.1 Audio Modulation and Audio Amplification
Audio signal produced by external or internal microphone is amplified and limitted
by IC U7. The output signal enters to VCO through low pass filter and
U2. Max. Frequency modulation deviation is adjusted by VR1
Audio modulation and audio amplification has preemphasis characteristic of 6dB/OCT
by U7(NJM324V).
11. CHANNEL DATA
CH
Frequency (MHz)
CH
Local Oscillator (MHz)
1
446.00625
1
424.30625
2
446.01875
2
424.31875
3
446.03215
3
424.33215
4
446.04375
4
424.34375
5
446.05625
5
424.35625
6
446.06875
6
424.36875
7
446.08125
7
424.38125
8
446.09375
8
424.39375
