4-2 TRANSMITTER CIRCUITS
4-2-1 MICROPHONE AMPLIFIER CIRCUIT (RC-26, MAIN AND DSP UNITS)
The microphone amplifier circuit amplifies microphone audio signal to a level needed for the DSP circuit.
Audio signals from the [MIC] connector (J8701, pin 6) are amplified at the AF amplifier (IC8280, pin 3), and then applied to the gate modulator IC (MAIN unit; IC2001, pin 3) via the J2051, pin 1 as “FMOD” signal. The signal is applied to the DSP unit after being passed through the AF amplifier and
4-2-2 DSP TRANSMITTER CIRCUIT (DSP UNIT)
The DSP (Digital Signal Processor) circuit enables PSN (Phase Shift Network)/Low Power/Phase modulator, trans- mitter monitor, side tone, and etc.
The microphone audio signals from the MAIN unit via the “DSPI1” line are amplified at the differential amplifiers (IC9651a/b), and are then applied to the A/D converter sec- tion in the CODEC IC (IC9501). at the same time, the con- verted signals are
The level shifted signals are applied to the DSP IC (IC9301) and modulated at the DSP IC to produce the 12 kHz trans- mitter IF signal.
The modulated IF signal from the DSP IC is applied to the D/A convertor section in the CODEC IC (IC9501) to convert into the analog IF signal. Also the signal is
The
When the speech compressor function is ON, the
At the same time, the compressed signals are modulated at the DSP IC and applied to the D/A converter section in the CODEC IC (IC9501).
4-2-4 IF AMPLIFIER AND MIXER CIRCUITS (MAIN UNIT)
The modulated 3rd IF signal from the DSP unit (“DSPO1” signal: 12 kHz) passes through the transmit/receive switch (IC1703, pins 1, 6), and then applied to the 3rd mixer circuit (IC901, pin 3). The applied 3rd IF signal is mixed with the 3rd LO signal from the DDS circuit (PLL unit; IC5701) to pro- duce a 455 kHz 2nd IF signal.
The 2nd IF signal is output from IC901, pin 5 and passes through the ceramic bandpass filter (FL402) to suppress the unwanted signals via the D132. The filtered 2nd IF signal is amplified at the 2nd IF amplifier (Q801), and then applied to the 2nd mixer circuit after being passed through the D305 and
The 2nd IFsignal is mixed with 64 MHz 2nd LO signal, com- ing from the PLL circuit, at the 2nd mixer circuit (D303) to obtain 64.455 MHz 1st IF signal. The 1st IF signal is passed through the bandpass filter (FI1201) to cut off the unwanted signals. The signal is applied to the transmitter mixer circuit (Q702, Q703) to obtain the desired signal via the transmit/receive switch (D205) and attenuator (R712, R715, R716).
The operating (transmitting) frequency is produced at the 1st IF mixer circuit (Q702, Q703) by mixing the 1st IF and 1st LO signals. The mixed signal is then applied to the RF cir- cuit.
4-2-3 SPEECH COMPRESSOR CIRCUIT (DSP UNIT)
The DSP (Digital Signal Processor) circuit enables PSN. The speech compressor compresses the transmitter audio input signals to increase the average output level (average talk power).
• TRANSMIT CONSTRUCTION
MIC 
Controller
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| 3rd LO |
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| IC2001 | IC1051 |
| 7 | 1 | DSP | 455 kHz | Ceramic | Q801 | |
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| 3 AMP. 1 5 LPF | 7 | 6 | AMP. | |||||
AMP. | VCA | DSPI1 UNIT | DSPO1 | BPF | ||||||
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| IC1001 |
| (12 kHz) | FI402 |
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| 2nd mixer |
| FI201 | 1st mixer | ||||
| D303 |
| Q702, Q703 | |||||
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| 64.455 kHz |
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| RF |
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| BPF |
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| Q401 | ||
2nd LO (64.00 MHz) |
| 15 kHz | 1st | LO | ||||
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0.5 1.9999 MHz |
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IC1 |
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| LPF |
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| Q6106, Q6401, | |
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Antenna
FILTER UNIT
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| D7271, | |
| D7272 |
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