SECTION 5 CIRCUIT DESCRIPTION
5-1 RECEIVER CIRCUITS
RF CIRCUITS
The antenna switching circuit toggles between the receive (RX) line and transmit (TX) line. RF amplifi er amplifi es the received signals within the frequency coverage.
Received signals from the antenna are passed through Low Pass filter (LPF; L40, C369, C370), TX power detector (D47, D49, D51) and another LPF (L38, L39, C343, C345, C356, C357), then applied to the antenna switching circuit (D38/ D39, L37, C337, C346).
The received signals are passed through the antenna switching circuit as an LPF (L37, C337, C346), LPF (L35, C322, C322, C323, C336) and
The 1st IF signal from the 1st IF amplifier (Q12) is applied to the IF IC (IC5, pin 16). The applied signal is converted into the 2nd IF signal by being mixed with the 2nd LO signal from X1 via tripler (Q3, L3, L2, C32−C35).
The converted 2nd IF signal is output from pin 3, and passed through the 2nd IF filter (FI1). The filtered 2nd IF signal is passed through (bypassed) another 2nd IF filter (FI2) via filter switches (D1 on input side; D2 on output side). The filtered signal is then applied to the IF IC (IC5, pin 5), and amplified by 2nd IF amplifier. The amplified signal is
The demodulated AF signals are output from pin 9, then applied to the AF circuits.
The amplified signals are passed through another two- staged tuned BPF (D27, L28, C260−C263, C242 and D26, L26, C219, C220, C240) and applied to the 1st mixer (IC10; pins 4, 5, L18, L19, L24).
1ST IF CIRCUITS
The amplified received signals from the RF circuit are converted into the 1st IF signal, fi ltered and amplifi ed at the 1st IF circuits.
The received signals from the RF circuits are mixed with 1st Local Oscillator (LO) signal from the RX VCOs, to be converted into the 1st IF signal. The converted 1st IF signal is amplified by 1st IF amplifier (Q50). The amplified 1st IF signal is passed through the 1st IF filter (FI3 for analog mode, FI4 for digital mode) via filter switches (Q20, D21, D66, D67 on input side; D6, D68, D69 on output side) to suppress unwanted signals. The filtered 1st IF signal is amplified by another 1st IF amplifier (Q12), then applied to the 2nd IF circuits.
2ND IF CIRCUITS
The 1st IF signal is converted into the 2nd IF signal, amplified and demodulated in the IF IC.
AF CIRCUITS
The demodulated AF signals from the IF IC are amplified and fi ltered 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 IF IC (IC5, pin 9) are passed through Digital/Analog switch (IC8, pins 2, 15), and applied to the base band IC (IC2, pin 23).
The applied AF signals are amplified at the amplifier section and level adjusted at the volume controller section, then suppressed unwanted 3 kHz and higher audio signals at LPF. The filtered AF signals are applied (bypassed) the TX/ RX HPF, scrambler,
The TX/RX HPF filters out 250 Hz and lower audio signals, and the
The AF signals are then level adjusted at the volume controller section and amplified at the amplifier section, then output from pin 20 (IC2).
• 2nd IF AND DEMODULATOR CIRCUITS | D2 | D1 |
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| N/W | N/W |
| SW | SW |
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| FI2 |
FI1 | 45.9 MHz |
| Q3 | |
BPF | 3 | |||
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2
D/A converter (IC6)
1
Demodulated signals to the AF circuits
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| 8 | 7 | 5 | 3 | 2 |
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| Filter |
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| Noise | X1 |
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| amp. |
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| detector | 15.3 MHz |
Quadrature |
| Limiter |
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| amp. |
| Mixer |
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detector |
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| RSSI |
| IF IC (IC5) |
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9 | 10 | 11 | Q13 | 12 | 13 | 16 |
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| 1st IF signal from the IF amplifier (Q12) | |
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| Buffer |
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| “NOIS” signal to the CPU (IC14: pin 113) | |
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+5V
“RSSI” signal to the CPU (IC14: pin 71)
X3 | “D_IF” signal to the optional digital unit via J2 |
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5 - 1