ALAN Electronics Tectalk FM PMR 446, Руководство по обслуживанию

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e) Squelch Circuit
Noise component of detected outputs has amplification
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 pin5 through C220, it comes out to pin5 Then, It reaches
the speaker.
5.3 Transmitter
When Tx develops 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 harmonic.
5.3-1 Audio Modulation and Audio Amplification
Audio signal produced by external or internal microphone, limits
amplification by IC U7.. It enters to VCO through low pass filter
and U2.
Max. Frequency modulation deviation is adjusted by VR1 keeps noise
and audio from entering to VCO at time of Tx.
Audio modulation and Audio Amplification has characteristic of
6dB/OCT pre-emphasis by U7(NJM324V).