3-2 TRANSMITTER CIRCUITS

3-2-1 MICROPHONE AMPLIFIER CIRCUIT (RC-25, 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 1) 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 limitter amplifier and low-pass filter IC (MAIN unit; IC1051, pins 3, 7) as “DSPI1” signal.

3-2-2 DSP TRANSMITTER CIRCUIT (DSP UNIT)

The DSP (Digital Signal Processor) circuit enables PSN (Phase Shift Network)/Low Power/Phase modulator, transmitter monitor, side tone, and etc.

The microphone audio signals from the MAIN unit via the “DISPI1” line are amplified at the differential amplifiers (IC651a/b), and are then applied to the A/D converter section in the CODEC IC (IC501). at the same time, the converted signals are level-shifted 5 V to 3.3 V in the IC (IC501).

The level shifted signals are applied to the DSP IC (IC301) and modulated at the DSP IC to p[roduce the 12 kHz transmitter IF signal.

The modulated IF signal from the DSP IC is applied to the D/A convertor section in the CODEC IC (IC501) to convert into the analog IF signal. Also the signal is level-shifted 3.3 V to 5 V at the level converter section in the IC (IC501).

The level-shifted IF signal is passed through the active filter (IC701a), and then applied to the MAIN unit via J901 (pin 17) as the “DSPO1” signal.

When the speech compressor function is ON, the level-shifted signal from the CODEC IC (IC501) is applied to the DSP IC (IC301) and compressed at the DSP IC to obtain an average audio level.

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 (IC501).

3-2-4 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 swtich (IC1703, pins 1, 5), 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 produce 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 D404. 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 D303 and low-pass filter (L304–L306, C304–C311, R306).

The 2nd IFsignal is mixed with 64 MHz 2nd LO signal, coming from the PLL circuit, at the 2nd mixer circuit (D302) to obtain 64.455 MHz 1st IF signal. The 1st IF signal is passed through the crystal bandpass filter (FI301A, FI301B) 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 (D301) and attenuator.

The operating (transmitting) frequency is produced at the 1st IF mixer circuit (Q210, Q202) by mixing the 1st IF and 1st LO signals. The mixed signal is then applied to the RF cir- cuit.

3-2-3 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

 

 

 

 

3rd LO

 

 

 

 

 

 

 

 

 

 

(443 kHz)

 

 

 

 

 

IC2001

IC1051

7

1

DSP

 

455 kHz

Ceramic

 

Q801

 

 

 

 

 

3 AMP. 1 5 LPF 7

6

 

 

AMP.

 

MIC Controller AMP. VCA

DSPI1 UNIT

DSPO1

BPF

 

 

 

 

 

 

IC1001

 

(12 kHz)

FI402

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Antenna

 

2nd mixer

 

FI301b/a

1st mixer

0.5—1.9999 MHz

PA UNIT

FILTER UNIT

 

D302

 

Q702, Q703

 

 

 

 

 

 

 

 

 

 

64.455 kHz

 

Crystal

 

 

RF

 

 

 

LPF

 

 

 

 

YGR

 

 

AMPs

LPFs

PWR

 

 

 

 

 

 

BPF

 

 

amp.

 

 

 

 

 

 

 

 

 

DET

 

 

 

 

 

Bandwidth:

 

Q401

 

 

 

 

 

 

 

 

 

IC1

Q6101, Q6801,

 

D7271,

2nd LO (64.00 MHz)

 

15 kHz

1st LO

 

 

 

 

 

 

 

 

 

 

D7272

 

 

 

 

 

 

 

(64—94 MHz)

 

 

 

BPFs

 

 

 

 

Q6851, Q6401,

 

 

 

 

 

 

 

 

 

 

 

 

2—30 MHz

 

Q6402

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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