SECTION 5 CIRCUIT DESCRIPTION
5-1 RECEIVER CIRCUITS
5-1-1 ANTENNA SWITCH (MAIN and RF UNITS)
The received signals from the antenna connector are passed through the antenna switch which toggles the receive (RX) line and transmit (TX) line.
The received signals from the antenna connector are passed through the
While transmitting, the voltage on the T5V line is applied to D601 and D603, and these are ON. Thus the TX line is connected to the antenna. Simultaneously, the RX line is connected to the GND to prevent transmit signal entering.
While receiving, no voltage is applied to the D601 and D603, and these are OFF. Thus the TX line and the antenna is disconnected to prevent received signals entering. Simultaneously, the RX line is disconnected from the GND and the received signals are passed through the LPF (RF UNIT; L604, C611, C612, MAIN UNIT; L29, C117).
The filtered signals from the LPF (RF UNIT; L604, C611, C612, MAIN UNIT; L29, C117) are then applied to the RF circuit via the two staged tunable bandpass filter (BPF; D23, D24, L31, L32, C120−C122, C125−C127).
5-1-2 RF CIRCUIT (MAIN UNIT)
The received signals are filtered and amplified at the RF circuit.
The fi ltered signals are applied to the RF amplifi er (Q10). The amplified signals are applied to the 1st mixer (Q37) via another
5-1-3 1st IF CIRCUITS
The received signals are converted into the 1st IF signal, and amplified at the 1st IF circuits.
The filtered signals from the RF circuit are converted into the
46.35MHz 1st IF signal by being mixed with the 1st Local Oscillator (LO) signals from the VCO (155 MHz and below; Q1, D1 −D4, 155 MHz and higher; Q2, D5−D8) at the 1st mixer (Q37).
The converted 1st IF signal is passed through the 1st IF filter (in wide mode; FI1, in narrow mode; FI4) via the bandwidth switch (D34), to remove adjacent signals. The filtered signal is applied to the 1st IF amplifi er (Q25) via another bandwidth switch (D35). The amplified 1st IF signal is then applied to the FM IF IC (IC3, pin 16).
5-1-4 2nd IF AND DEMODULATOR CIRCUITS (MAIN UNIT)
The 1st IF signal is converted into the 2nd IF signal, and de- modulated.
The 1st IF signal from the 1st IF amplifier (Q25) is applied to the 2nd IF mixer in the FM IF IC (IC3, pin 6). And the 1st IF signal is converted into the 450 kHz 2nd IF signal by being mixed with the 2nd LO signal from the reference frequency oscillator (X1) via the tripler (Q18).
The converted 2nd IF signal is output from pin 3, and passed through the 2nd IF fi lter (FI2) to suppress sideband noise. In narrow mode, the 2nd IF signal is also passed through another 2nd IF fi lter (FI3) via bandwidth switches (D32, D33).
The fi ltered 2nd IF signal is applied to the limiter amplifi er in the FM IF IC (IC3, pin 5). The amplifi ed 2nd IF signal is FM- demodulated at the quadrature detector (X5, IC3, pins 10, 11) and output from pin 9. The demodulated AF signals are then applied to the AF circuits.
5-1-5 AF CIRCUITS (FRONT and MAIN UNITS)
The demodulated AF signals from the FM IF IC are amplified and filtered at AF circuits. This transceiver employs the base band IC for audio signal processing for both transmit and receive. The base band IC is an audio processor and composed of
The demodulated AF signals from the FM IF IC (IC3, pin 9) are applied to the base band IC (IC5, 23) via the Digital/Analog switch (IC14, pins 2, 15).
The applied AF signals are amplifi ed at the amplifi er (RXA1) and level adjusted at the volume controller (VR3), then suppressed unwanted 3 kHz and higher audio signals at LPF. The filtered AF signals are applied or bypassed the TX/RX HPF, scrambler,
• 2nd IF AND DEMODULATOR CIRCUITS |
| D33 | D32 |
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| N/W | N/W |
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| SW | SW |
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| FI2 | 45.9 MHz |
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| BPF | 3 | ||
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| 8 | 7 | 5 | 3 | 2 |
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| Filter |
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D/A converter |
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| Limiter |
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(IC4) |
| Quadrature |
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| Mixer |
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| detector |
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Demodulated signals |
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| FM IF IC (IC3) | ||
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| 9 | 10 | 11 | 12 | 13 | 16 |
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to the AF circuits |
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| 1st IF signal from the IF amplifier (Q25) | |||
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| “NOIS” signal to the CPU (IC18: pin 37) | ||
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| “RSSI” signal to the CPU (IC18: pin 50) | ||
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| X5 |
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5 - 1