Icom IC-V8000 service manual Transmitter Circuits

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The AF signals are applied to the AF power amplifier circuit (IC9, pin 1) to obtain the specified audio level. The amplified AF signals, output from pin 4, are applied to the internal speaker (CHASSIS UNIT; SP1) via the speaker jack (J6) when no plug is connected to the external speaker jack (J1).

4-1-6 SQUELCH CIRCUIT (MAIN AND LOGIC UNITS)

A squelch circuit cuts out AF signals when no RF signals are received. By detecting noise components in the AF signals, the squelch switches the analog swtich.

A portion of the AF signals from the FM IF IC (IC4, pin 9) are applied to the D/A converter (IC5, pin 13) as the DETO sig- nal. The signals from the D/A converter (IC5, pin 14) are applied to the FM IF IC active filter section (IC4, pin 8) where noise components are amplified and detected with an inter- nal noise detector via the SQLIN line.

The trigger circuit converts the detected signals to a HIGH or LOW signal and applies this (from pin 13) to the CPU (LOGIC UNIT; IC7, pin 19) as the NOIS signal.The CPU controls the analog swtich IC (LOGIC UNIT; IC6) via the expander IC (LOGIC UNIT; IC8). When the CPU receives a HIGH level NOIS signal, the CPU controls the RMUT line to cut the AF signals at the analog swtich IC (LOGIC UNIT; IC6). At the same time, the AFON line controls the AF mute circuit (Q29) to cut out the VOLOUT signal for the AF power amplifier (IC9).

4-2 TRANSMITTER CIRCUITS

4-2-1 MICROPHONE AMPLIFIER CIRCUIT (LOGIC AND MAIN UNITS)

The microphone amplifier circuit amplifies audio signals with +6 dB/octave pre-emphasis from the microphone to a level needed for the modulation circuit.

The AF signals from the microphone pass through the MIC switch (IC2, D4) and high-pass filter (IC3a, pin 2), and are then applied to the microphone amplifier circuit (IC3d, pin

12)via the R39 and C47 for +6 dB/octave pre-emphasis. The amplified AF signals are applied to the analog swtich (IC6, pin 4), and are then applied to the D/A converter (MAIN UNIT; IC5, pin 1) via the MODIN signal. The AF signals are applied to the modulator circuit via the MOD signal.

4-2-2 MODULATION CIRCUIT (MAIN UNIT)

The modulation circuit modulates the VCO oscillating signal (RF signal) using the microphone audio signals.

The audio signals (SHIFT) change the reactance of D2 to modulate an oscillated signal at the VCO (Q6, D4). The oscillated signal is amplified at the LO (Q9) and buffer (Q11) amplifiers, then applied to the TX/RX switch circuit (D6, D7).

4-2-3 DRIVE/POWER AMPLIFIER CIRCUITS (MAIN UNIT)

The signal from the VCO circuit passes through the TX/RX swtiching circuit (D6) and is amplified at the pre-drive (Q17), drive (Q18, Q20) and power (Q23) amplifiers to obtain 75 W of RF power (at 13.8 V DC/typical). The amplified signal passes through the low-pass filter (L37, L39, C151, C156, C159, C167, C176, C227–C229), and then applied to the antenna swtiching circuit (D12). The signal is applied to the antenna connector (CHASSIS UNIT; J1) after being passed through the low-pass filter (L44, L47, L48, L51, C190, C197, C203, C208, C210, C217, C218).

The bias current of the drive (Q18, Q20) and power (Q23) amplifiers is controlled by the APC circuit to stabilize the out- put power.

4-2-4 APC CIRCUIT (MAIN UNIT)

The APC (Automatic Power Control) circuit (IC6a, Q26) pro- tects drive and power amplifiers from excessive currents and selects HIGH or LOW output power.

The output voltage from the power detector circuit (D14, D17) is applied to the differential amplifier (IC6a, pin 2), and the “T3” signal from the D/A converter (IC5, pin 23) is applied to the other input for reference.

When the driving current increases, the input voltage of the differential amplifier (IC6a, pin 2) will be increased. In such cases, the differential amplifier output voltage (pin 1) is decreased to reduce the drive current.

Q26 is controlled by the TXC signal from the expander IC (IC2, pin 14) to select HIGH or LOW output power.

• APC CIRCUIT

HV

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SWHV

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RF signal from

Q18

 

Q20

 

Q23

 

ANT

Driver

 

Driver

 

Power

 

PLL IC (IC1)

 

 

 

SW

amp.

 

amp.

 

amp.

 

 

 

 

 

 

+5V

 

 

TXC

2

 

 

1

Q26

IC6a

 

 

T1

3

 

+

 

 

 

APC control circuit

L44, C190, C191, C196, C197

LPF to antenna

D14 D12

Power detector circuit (D12, D14)

4 - 2

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Contents VHF FM Transceiver Repair Notes IntroductionOrdering Parts Table of Contents Specifications ‘ General‘ Transmitter ‘ ReceiverLogic Board Inside ViewsMain Unit Disassembly and Option Instructions Optional Unit InstallationRemoving the Cover Removing the Main Unit Removing the Front PanelCircuit Description Receiver CircuitsTransmitter Circuits Power Supply Circuits PLL CircuitsPin Port Description Number Name Port AllocationsCPU Logic Unit IC7 Pin Port Description Number 2 D/A Convertor IC Main Unit IC53 I/O Expander IC Main Unit IC2 Parts List Order DescriptionElectrolytic ECEV1CA100SR Diode HVU131TRF Tantalum ECST1VY334R Tantalum ECST1CX106R Chassis Parts Mechanical Parts and DisassemblyAccessories Page 32, Kamiminami, Hirano-ku, Osaka, 547-0003, Japan

IC-V8000 specifications

The Icom IC-V8000 is a powerful mobile transceiver that has made a mark among amateur radio enthusiasts due to its impressive features and robust performance. It operates on the VHF band and boasts a broad frequency range, making it ideal for both local and long-distance communication. The Icom IC-V8000 is perfect for those who need a reliable and versatile radio for various applications, from mobile use in vehicles to stationary use in remote locations.

One of the standout features of the IC-V8000 is its high power output capability, offering up to 75 watts of transmit power. This allows users to achieve extended range communication without the need for additional amplifiers. The transceiver also has a dual band capability, allowing it to receive on VHF and UHF frequencies, which expands its functionality and usefulness in different communication scenarios.

The radio includes advanced digital signal processing (DSP) technology that enhances audio clarity by minimizing background noise and improving overall sound quality. This is particularly useful during crowded band conditions or when communicating with stations at the edge of range. The IC-V8000 is also equipped with a wide variety of scanning features, including memory channel scanning and priority scanning, which enable users to keep track of multiple frequencies simultaneously.

The IC-V8000 features a large, easy-to-read LCD display that provides vital information at a glance. The display is backlit, making it easy to read in low-light conditions. The user interface is intuitive and user-friendly, allowing quick access to essential controls and functions. The transceiver supports a range of accessories, including external microphones and speaker systems, which can enhance the overall communication experience.

Another notable characteristic of the Icom IC-V8000 is its rugged construction. Built with durability in mind, the radio can withstand the rigors of mobile use, making it suitable for various environments. Additionally, it has a built-in thermal protection system to prevent overheating during extended use.

In conclusion, the Icom IC-V8000 is an exceptional VHF mobile transceiver that combines high power output, advanced technology, and user-friendly features. Whether for everyday communication, emergency services, or casual hobby use, the IC-V8000 stands out as a versatile and dependable choice in the world of amateur radio. Its robust performance and comprehensive feature set make it a favorite among avid radio operators.
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