Icom IC-910H service manual PLL Circuits

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low-pass filter and UHF signal are high-pass filter, and then applied to the VHF and UHF power amplifier circuit sepa- rately.

4-2-7 POWER AMPLIFIER CIRCUIT (PA UNIT)

The power amplifier circuit amplifies the RF signals to the specified output power.

(1) VHF power amplifier circuit

The RF signal from the low-pass filter circuit is applied to the VHF power amplifier circuit (Q651, Q652) to obtain a stable 100 W of RF output power. The amplified RF signal is applied to the antenna connector (CHASSIS; J1) via the power detector (D720, D721), transmit/receive switching relay (RL700) and low-pass filter (L723–L721, C728–C726, C728) circuits.

(2) UHF power amplifier circuit

The RF signal from the high-pass filter is applied to the UHF power amplifier circuit (Q151, Q152) to obtain a sta- ble 75 W of RF output power. The amplified RF signal is applied to the antenna connector (CHASSIS; J2) via the transmit/receive switching circuit (D182–D185), low-pass filter (L181, L180, C188–C184) and power detector (D180, D181) circuits.

4-2-8 ALC CIRCUIT (PA AND MAIN UNITS)

The ALC (Automatic Level Control) circuit protects the power amplifiers (PA unit; Q651, Q652 for VHF and Q151, Q152 for UHF) from a mismatched output load. Also, the ALC circuit controls the gain of the transmit IF amplifier in order for the transceiver to output even when the supplied voltage shifts, etc.

The RF power level is detected at the power detector circuit (PA unit; D720–D721 for VHF, D180, D181 for UHF) to be converted into DC voltages. The detected voltage (VFOR for VHF or UFOR for UHF) is passed through the switching diode, and are then applied to the differential amplifier (MAIN unit; IC1601b) via the FOR line. A reference voltage (POCV) for IC1601b is controlled by the [RF PWR] control to output reference voltages. The output voltage is applied to the transmit IF amplifier circuit (MAIN unit; Q1) as an ALC signal to control the amplifier gain.

When the VFOR/UFOR voltage increased, the output from the differential amplifier will be decrease to reduce the IF amplifier gain. This adjusts the RF output power until the VFOR/UFOR and POCV voltage are well balanced.

4-3 PLL CIRCUITS

IC-910H contains 2 PLL circuits and 1 local oscillator. The VHF and UHF PLL circuits adopt “Icom’s original I-loop PLL” to obtain very fast lock up times.

4-3-1 VHF PLL CIRCUIT (PLL UNIT)

The VHF PLL circuit generates the 1st LO frequency, and the signal is applied to the VHF 1st mixer circuit in the PA unit as the “A1LO” signal. The PLL circuit consists of a VCO, prescaler and DDS circuits.

The signal generated at the VHF VCO circuit (Q191, D191–D194) is amplified at the buffer amplifiers (Q192, Q272), then applied to the prescaler circuit (IC271). The prescaler circuit divides the applied signal, and outputs it to the VHF DDS circuit (IC131) via the buffer amplifier (Q271). The VHF DDS circuit generates digital signals using the applied signals as a clock frequency. The phase detector section in IC131 compares its phase with the reference fre- quency that is generated at the reference oscillator (X512). IC131 outputs off-phase components as pulse signals via pins 51, 52.

The output pulses are converted into DC voltage at the loop filter circuit (IC161a) and then applied to the VHF VCO cir- cuit.

The D/A converter (R101–R124), low-pass filter (L101–L103, C103–C110) and buffer amplifier (IC101) cir- cuits are connected to the DDS output to convert the digital oscillated signals into smooth analog signals.

4-3-2 UHF PLL CIRCUIT (PLL UNIT)

The UHF PLL circuit generates the 1st LO frequency, and the signal is applied to the UHF 1st mixer circuit in the PA unit as the “B1LO” signal. The PLL circuit consists of a VCO, prescaler and DDS circuits.

The signal generated at the UHF VCO circuit (Q391, D391–D394) is amplified at the buffer amplifiers (Q392, Q472), then applied to the prescaler circuit (IC471). The prescaler circuit divides the applied signal, and outputs it to the UHF DDS circuit (IC331) via the buffer amplifier (Q471).

The D/A converter (R301–R324), low-pass filter (L301–L303, C103–C311) and buffer amplifier (IC301) cir- cuits are connected to the DDS output to convert the digital oscillated signals into smooth analog signals.

4-2-9 APC CIRCUIT (MAIN UNIT)

The APC (Automatic Power Control) circuit protects the power amplifiers on the PA unit from excessive current.

Current drain of power amplifiers is detected by voltage drops at a resistor (PA unit; R305) between VCC and PAHV lines. The original voltage (ICH) and dropped voltage (ICL) are applied to the APC differential amplifier (MAIN unit; IC1601d).

The signal output from the differential amplifier reduces IF amplifier gain until these voltages are well-balanced.

4-4 UX-910 (1200 MHz BAND UNIT)

UX-910 is an optional 1200 MHz band unit for IC-910H. This unit covers 1240–1300 MHz frequency range.

4-4-1 ANTENNA SWITCHING CIRCUIT (for RX)

Received signals from the antenna connector (CHASSIS; J501) are applied to the transmit/receive switching circuit (RL51).

The transmit/receive switching circuit leads receive signal to the RF circuit while receiving. However, the circuit leads the transmit signal from the RF power amplifier to the antenna connector while transmitting.

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Contents Service Manual Ordering Parts IntroductionRepair Notes EURTable of Contents General SpecificationsReceiver Inside Views SectionMain and PLL Units FM if ICPA Unit PLL IC TOP ViewBottom View UX-910 1200MHz Band Unit Disassembly and Option InstructionsOpening the transceiver’s case Main SUB Opening the PA unit coverFL-132/FL-133 CW Narrow Filter Installing 2nd DSP unit rear panel side Installing 1st DSP unit front panel sideUT-102 Voice Synthesizer Unit UT-106 DSP UnitCR-293 High Stability Crystal Unit Receiver Circuit Circuit DescriptionDemodulator Circuit Main Unit 6 10 MHz if Circuit Main UnitSquelch Control Circuit Main Unit Squelch Circuit Main UnitNoise Blanker Circuit Main Unit Transmitter CircuitsAGC Circuit Main Unit Meter Circuit Main UnitModulation Circuit Main Unit Transmit if Amplifier Circuit Main UnitCW Keying Circuit Main Unit RF Circuit PA UnitPLL Circuits 8 2LO PLL Circuit PLL Circuits7 1LO PLL Circuit Preparation Before Sarvicing Adjustment ProceduresRequired Test Equipment ‘ ConnectionsFrequency Adjustment PLL AdjustmentsPLL and Main Units Receiver Adjustments P501 R547L353 L354 R360Noise EXTBlanker Main Band OFFL22 L283CP851 CP852Transmitter Adjustments C659 R503R138 R131Main Gain If TotalGND LO LeakR202 R504CP1613 R1613Software Adjustment Meter Software AdjustmentNoise SQL Calibration FilterTX Power LPF DeviationHPF OFF UX-910 Adjustments CP322 CP321C332 R13APC Power SETPre-setting for APC adjustment Display Board Section Parts ListFront Unit Resistor ERA3YED VR-B Board Func BoardVR-A Board Jack Board RIT BoardMIC Board PLL UnitResistor ERA3YEB Thermistor Tantalum ECST1AD107R REG BA09T Main UnitDiode DAN222TL Resistor ERA3YKD R364 7030003320 R915 7030003520 Tantalum Temsva 1C 335M-8L Electrolytic ECEV1EA4R7SR Electrolytic Relay Diode HSU88TRF Coil Eljre 15NG-F Resistor ERJ1WYJ181U Resistor ERJ1TYJ102U JB 1H JB 1C Mica BARISTOR-A Board DRV BoardVARISTOR-B Board BARISTOR-C BoardMain Unit UX-910 2UX-910MAIN UnitResistor RGB3L R15 Resister ERA3YED Tantalum ECST1CC226R CH 1H Connectot 25FMN-BTK Display Unit Mechanical PartsCover Parts Chassis PartsUX-910 Chassis Parts UnpackingUX-910 Main Unit UX-910 UnpackingTransistors and FET’S SEMI-CONDUCTOR InformationDTA114 EE TL MA29B DiodesSection Board Layouts Page Icom America Inc 13714HZ-C1

IC-910H specifications

The Icom IC-910H is a highly regarded and versatile transceiver that is designed for amateur radio operators who are particularly interested in V/UHF and microwave communications. Known for its exceptional performance, the IC-910H encompasses a suite of features that make it a standout choice for both casual and dedicated hams.

One of the main features of the IC-910H is its dual-band capability, allowing for simultaneous operation on both 144 MHz (2 meters) and 430 MHz (70 centimeters) bands. This dual operation enables users to engage in various communication modes, including SSB, CW, FM, and digital. Its high frequency stability ensures that users can rely on the transceiver for accurate and consistent transmissions.

The IC-910H is equipped with a high-performance 10 MHz IF filter that improves selectivity and reduces adjacent channel interference. The optional 1.2 GHz module enhances the transceiver’s capabilities, allowing operators to venture into microwave frequencies. This expandability is a significant advantage for users who wish to progress in their amateur radio pursuits.

Another notable aspect of the IC-910H is its large, easy-to-read LCD display, which features various color options for enhanced visibility. The front panel layout is user-friendly, providing quick access to important controls and functions. The built-in DSP (Digital Signal Processing) technology offers noise reduction and filtering capabilities, significantly improving overall audio quality and making weak signals more intelligible.

The transceiver also includes extensive memory functions, with up to 1,000 memory channels available for storing frequencies, modes, and operational settings. Additionally, it supports CTCSS and DCS tones, which facilitate the use of repeater systems and private group communications.

In terms of build quality, the IC-910H features a robust construction designed for durability and long-term use. Its efficient power supply management ensures excellent performance while minimizing heat generation, making it suitable for extended operating sessions.

Overall, the Icom IC-910H is a powerful and feature-rich transceiver that is favored by many amateur radio enthusiasts. With its versatile operating modes, advanced filtering capabilities, and clear display, it stands out as a reliable tool for both casual operators and serious DXers. Its well-thought-out design and comprehensive features make it a valuable addition to any ham's station collection.
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