Circuit Description

The resulting DC squelch control voltage is passed to pin 19 of the microprocessor Q1050. If no carrier is received, this signal causes pin 6 of Q1052 (BU2090FS) to go low and pin 89 of Q1050 to go high. Pin 6 of Q1052 signals Q1008 (CPH6102), Q1017 (UMC5N) and Q1020 (UMC5N) to disable the

supply voltage to audio amplifiers Q1007 and Q1011, while pin 89 makes Q1014 (UMG2N) hold

the green (Busy) half of the LED off, when pin 6 of Q1052 is low and pin 89 of Q1052 is high.

Thus, the microprocessor blocks output from the au-

dio amplifier, and silences the receiver while no sig-

nal is being received, and also during transmission.

When a carrier appears at the discriminator, noise is removed from the output, causing pin 19 of Q1048

to go low and the microprocessor to blink the busy LED via Q1052.

The microprocessor then checks the DTMF decoder

chip on the Optional Unit, the CTCSS and the CDCSS

code for DTMF or CTCSS or CDCSS code squelch in-

formation, if enabled, respectively. If not transmitting

and CTCSS or CDCSS is not activated, or if the re-

ceived tone or code matches that programmed, the

microprocessor stops scanning, if active, and allows

audio to pass through the audio amplifier Q1007 and Q1011 (TDA2822D) to the loudspeaker by enabling the supply voltage to it via Q1008, Q1017 and Q1020.

Transmit Signal Path

Microphone Amplifier

Speech input from the microphone is amplified in Q1022 (NJM2902V), is filtered, and is sent to Q1021 (M62364FP) and sent to the Dummy Unit (or Op-

tional Unit). The audio which returned from the Dummy Unit passes through Q1027 (AK2345) to be

pre-emphasized.

The processed audio is then mixed with a CTCSS tone

generated by microprocessor Q1050 and delivered to D1043 (HVC350) for frequency modulating the PLL

carrier up to ±5 kHz from the unmodulated carrier at

the transmitting frequency.

If an external microphone is used, PTT switching is controlled by Q1003 (UMZ2N), which signals the mi-

croprocessor when the impedance at the microphone

jack drops.

If a CDCSS code is enabled for transmission, the code is generated by Q1027 and delivered to D1061 (HVC350) for CDCSS modulation.

If DTMF is enabled for transmission, the tone is gen-

erated by the microprocessor Q1050 and applied to

the splatter filter (Q1028) in place of speech audio.

Also, the tone is amplified for monitoring in the

loudspeaker.

Noise Canceling Microphone Circuit

Two signals from separate internal microphones

(main and sub) are fed to the positive input (sub) and to the negative input (main) and of Q1022 (NJM2902V). If the same signal level is present at

both main and sub, the main signal will be canceled at the output of Pin 1 of Q1022. In other words, noise

from nearby sources not directly connected to the

transceiver enters the main and sub input at the same

signal and, in the absence of (stronger) voice input,

is therefore canceled out.

When a signal is only input to the main microphone,

and there is no signal at the sub microphone, the main signal is passed as-is from Q1022.

Drivers and Final Amplifiers

The modulated signal from the VCO, Q1041 (2SC4227-R34), is buffered by Q1032 (2SC5226-4/ 5) and amplified by Q1029 (2SC5226-4/5) and Q1026 (2SC3356-R25). The low-level transmit signal is then applied to the Power Module Q1016 (M68732HA-22) for final amplification up to a maxi-

mum of 5 Watts of output power.

The transmit signal then passes through the antenna switch D1016 (HVU131), and is low-pass filtered to

suppress harmonic spurious radiation before deliv-

ery to the antenna.

Automatic Transmit Power Control

RF power output from the final amplifier is sampled by C1020 and C1025, and is rectified by D1021 (RB715F). The resulting DC is fed back through Q1018 (NJM2902V) to the Power Module, provid-

ing control of the power output.

The microprocessor selects either "High" or one of

three "Low" power levels.

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