Alinco DR-135, Руководство по обслуживанию

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CIRCUIT DESCRIPTION DR-135/DR-235/DR-435
1) Receiver System (DR-135)
The receiver system is a double superheterodyne system with a 21.7 MHz first IF and a 450 kHz second IF.
1. Front End
The received signal at any frequency in the 136.000MHz to 173.995MHz range
is passed through the low-pass filter (L116, L115, L114, L113, C204, C203,
C202, C216 and C215) and tuning circuit (L105, L104 and D105, D104), and
amplified by the RF amplifier (Q107). The signal from Q107 is then passed
through the tuning circuit (L103, L102, and varicaps D103 and D102) and
converted into 21.7 MHz by the mixer (Q106). The tuning circuit, which
consists of L105, L104, varicaps D105 and D104, L103, L102, varicaps
D103 and D102, is controlled by the tracking voltage form the VCO. The local signal
from the VCO is passed through the buffer (IC112), and supplied to the source of
the mixer (Q106). The radio uses the lower side of the superheterodyne system.
2. IF Circuit
The mixer mixes the received signal with the local signal to obtain the sum of
and difference between them. The crystal filter (XF102, XF101) selects 21.7
MHz frequency from the results and eliminates the signals of the unwanted
frequencies. The first IF amplifier (Q105) then amplifies the signal of the selected
frequency.
3. Demodulator Circuit
After the signal is amplified by the first IF amplifier (Q105), it is input to pin 24 of
the demodulator IC (IC108). The second local signal of 21.25 MHz (shared
with PLL IC reference oscillation), which is oscillated by the internal oscillation
circuit in IC116 and crystal (X103), is input through pin 1 of IC108. Then, these
two signals are mixed by the internal mixer in IC108 and the result is converted
into the second IF signal with a frequency of 450 kHz. The second IF signal is
output from pin 3 of IC108 to the ceramic filter (FL101 or FL102), where the
unwanted frequency band of that signal is eliminated, and the resulting signal
is sent back to the IC108 through pins 5.
The second IF signal input via pin 5 is demodulated by the internal limiter
amplifier and quadrature detection circuit in IC108, and output as an audio
signal through pin 12.
4. Audio Circuit
The audio signal from pin 12 of IC108 is amplified by the audio amplifier
(IC104:A),and switched by the signal switch IC (IC111) and then input it to the
de-emphasis circuit.
and is compensated to the audio frequency characteristics in the de-emphasis
circuit (R203, R207, R213, R209, C191, C218, C217) and amplified by the AF
amplifier (IC104:D). The signal is then input to volume (VR1) . The adjusted signal is
sent to the audio power amplifier (IC117) through pin 1 to drive the speaker.