RELM RM8150 Series, Руководство по обслуживанию

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8
RM8150 SERVICE MANUAL
1st High frequency amplifier
Signals entering the antenna enters RF amplifier (Q26) via the trans-
-mitting/receiving switching circuit (D30/D31) and the band-pass filter
(L48, L38 and variodes: D50, D26). After being amplified, the signals
are filtered by the band-pass filters (L30, L51 and the variodes: D21,
D22) before entering the 1st mixer (Q21).
1st mixer
Signals from RF amplifier and the 1st local frequency from VCO are
synthesized to generate the 1st IF of 49.95MHz. And then the 1st IF
enters the 2 single-chip crystal filter (XF1 XF2) for further elimination
of parasitic signals and then sent to the IF amplifier
IF amplifier
After being amplified by Q19, the 1st IF signal enters U102 (Ta31136).
When the signal is mixed with the 2nd local signal in U102 again, the
2nd IF signal of 450kHz is generated. Before being amplified, the 2nd
IF enters the 450kHz ceramic filter (broad: CF1, narrow: CF2) for further
elimination of unnecessary signals as well as modulation and demo-
-dulation in U102.
Parameters of the receiving components
Item Rated Value
Rated central frequency 49.95MHz
Pass band width 5.0kHz or higher at 3dB
35dB stop band width 20.0kHz or lower
Pulse 1.0 dB or lower
Insertion loss 5.0 dB or lower
Guaranteed attenuation 80 dB or higher at fo 1MHz
Parasitic signal: 40 dB or
higher within fo 1MHz
Terminal impedance 350 /5.5 pF
Table 1 Crystal filterXF1/XF2
Item
Rated central frequency
Pass band width
35dB stop band width
Pulse
Insertion loss
Guaranteed attenuation
Terminal impedance
Rated Value
450kHz
6.0kHz or higher
12.5 kHz or lower
2.0 dB or lower
6.0 dB or lower
35.0 dB or higher within fo 100kHz
2.0k
Table 2 Ceramic filterCF1
Item
Rated central frequency
Pass band width
35dB stop band width
Pulse
Insertion loss
Guaranteed attenuation
Terminal impedance
Rated Value
450kHz
4.5kHz or higher
10.0 kHz or lower
2.0 dB or lower
6.0 dB or lower
60.0 dB or higher within fo 100kHz
2.0k
Table 3 Ceramic filter Cf2
Broad/Narrow switching circuit
The broadband control port (pin 51) and narrowband control port (pin
52) of the CPU are used for switching between ceramic filters. When
the broadband control port is at high level, the ceramic filter SW diode
(D13, D15) allows the CF1 to receive broadband signals. When the
narrowband control port is at high level, the ceramic filter SW diode
(D13, D15) will allows CF2 to receive narrowband signals (The circuit
is shown in the figure below).
IF demodulation TA31136
CF1
Wide
CF2
Narrow
D13
D15
Narrow
U401 PIN52
Wide
U401 PIN51
R74
R78
R73
R77
PIN 5
PIN3
Audio signal system
Detection s ignals from the IF IC (U102) enters the amplifier (U601) for
adjusting the gain and be outputted to AK2346(U404) for baseband
signal processing, the output signals are inputted to the audio power
amplifier (U11) for amplification and then be outputted from the speaker.
Squelch circuit
Noise signals outputted from FM IF chip (U102) output are amplified
by the voice amplifier (Q78), the DC voltage corresponding to the noise
level is regulated and outputted, the DC voltage is then sent to the
analog port of the CPU. U102 also outputs the DC level RSSI corres-
-ponding to the IF amplifier input signals.
Phase-locked loop frequency combiner
The phase-locked loop and the voltage controlled oscillator circuit
produce the 1st local oscillation signal of the receiver and the transm-
-itting signals of the transmitter.
Phase-locked loop circuit
The frequency step of the phase-locked loop circuit is 2.5/5.0/6.25kHz.
The reference oscillator signal of 16.8MHz is divided in the chip U101
through a mixer counter to produce reference frequency of 2.5/5.0
/6.25kHz. Signals outputted from the voltage controlled oscillator(VCO)
are buffer ed and amp lified via Q15 and then divided by the dual-mode
programmable counter in chip U405. Signals amplified by Q15 are
compared with phase comparators carrying reference signals with
2.5/5.0/6.25kHz in chip U101. Signals output from the phase compar-
-ator controls the voltage to enter a low-pass filter and to control the
oscillation frequency through the voltage controlled oscillator.
Voltage controlled oscillator
The RF rate is generated via Q11 in the transmission mode, the recei-
-ving frequency is generated via Q10 in the receiving mode. The control
signals ge nerate voltage via the phase comparator to the variode (D10
and D12 in the transmission mode, D9 and D11 in the receiving mode).
In the receiving mode, Q12 is cut and Q7 is connected, in the transm-
-ission mode, Q12 is connected and Q7 is disconnected. Output signals
from Q10 and Q11 are amplified by Q15 and sent to U405 frequency
divider.