RELM RMU800A, Руководство по обслуживанию

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RMU800A SERVICE MANUAL
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Circuit Description
1. Frequency Configuration
The receiver utilizes double conversion superheterodyne. The first IF is 73.05MHz and the second is
450KHz. The first local oscillator signal is supplied by PLL circuit. The second local oscillator signal
(73.5MHz) is generated from TCXO (73.5MHz); The PLL circuit also generates the frequencies needed
in the transmitter (See Fig.1).
Frequency Range: 450 MHz—512MHz
2. Receiver Circuit
The receiver section configuration is shown as Fig. 1.
Figure 1 Receiver Section Configuration
2.1 RF AMP BPF
It consists of BPF (D603, D602, D601) and RF amplifier (Q601). The range of bandpass frequency (U1:
400 MHz—470MHz
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U2: 450 MHz—512MHz U3: 480 MHz—526MHz
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U4: 440 MHz—490MHz
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U5: 350
MHz—400MHz). The signal is filtered by the RF Amp BPF to eliminate unwanted signals before going to
the first mixer.
2.2 The First Mixer
The signal from RF AMP BPF is mixed with the first local oscillator signal from PLL circuit in the
double-balance mixer (Q138, Q144, Q145, Q146) to generate a 73.05MHz first IF signal. The first IF
signal is then fed through two crystal filters (N: XF101, XF103; W: XF102, XF104) to further remove
spurious signals.