Alinco DJ-G5, Service Manual

Page: 5 / 73

5-2 R Band
A part of the audio signal of IC301 Ping is selected and amplified by the noise
amplifiers in R316, R317, R318, R319, C318, C319, C320, and IC301. Then it is
supplied from IC301 Pin11 to be amplified again in the noise amplifier (Q303). The
amplified noise factor is rectified in D301 , adjusted the level in VR30l , and applied
to CPU (IC508) Pin97, then converted to the dligital signal.
6 Attenuator Circuit
6-1 VHF Band
When the ATT key is pressed, "L" is applied from shift resistor (IC52) Pin14, and
D71 is turned ON, then the Attenuator circuit (Q56, R151, C194, R160) is acti­
vated.
The receiving signal passed through the low-pass filter is attenuated approximately
15dB by the attenuator to decrease the interference of the adjacent channel, etc.
6-2 UHF Band
When the ATT key is pressed, "L" is applied from shift resistor (IC52) Pin13, and
D55 is turned ON, then the Attenuator circuit (Q56, R73, C90, R80) is activated.
The receiving signal passed through the low-pass filter is attenuated approximately
15dB by the attenuator to decrease the interference of the adjacent channel, etc.
2) Transmitter System
1 Demodulation Circuit
The voice is converted into the electric signal by the internal or external micro­
phone, then it is applied to the mic amplifier (IC310). This IC310 has two opera­
tional amplifiers. The pre-emphasis and IDC consist of Pin1, 2 and 3, and the
splutter filter consists of Pin5, 6 and 7.
The output from the microphone amplifier is passed through variable resistors
VR305 and VR306 for maximum deviation adjustment to cathode of varicap diode
of the VCO, controlling the VCO frequency and so producing a frequency-modula-
tion.
2 Power Amplifier
2-1
The transmitting signal oscillated in VVCO is amplified in pre-drive amplifier (Q81)
and drive amplifier (Q80), then fed to the power module (IC54). The transmitting
signal amplified in IC54 is supplied to the antenna after attenuated the harmonics
enough in the antenna switch (D72) and the Low-pass filter (L90, L91 , L92, C220,
C229, C230,C231 , C235).
2-2
The transmitting signal oscillated in UVCO is amplified in pre-drive amplifier (Q54)
and drive amplifier (Q53), then fed to the power module (IC51). The transmitting
signal amplified in IC51 is supplied to the antenna after attenuated the harmonies
enough in the antenna switch (D52), and the bandi)ass filter (L57, L58, L53, L54,
C59, C60, C61, C66, C67, C68).
3 APC Circuit
3-1 VHF Band A part of transmitting voltage from low-pass filter is detected by D74, and con­
verted into the DC voltage. The converted detection voltage is differential ampli­
fied, and the output voltage controls the bias voltage of power module (IC54) Pin2
to fix the transmitting power.
3-2 UHF Band
A part of transmitting voltage from low-passS filter is detected by D56, and con­
verted into the DC voltage. The converted detection voltage is differential ampli­
fied, and the output power controls the bias voltage of power module (IC51) Pin2
to fix the transmitting power.
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