ICOM IC-280E 144MHz FM Transceiver

Introduction

The ICOM IC-280E is a 144MHz FM transceiver designed for amateur radio use. It features a microcomputer for frequency control, band-edge detection, and display, along with a 3-channel memory. The unit offers superior receiving characteristics due to low-noise FETs and helical cavity filters, and highly stable transmitting characteristics with a directly amplified VCO and a power module in the PA unit. The control unit is separable from the main body for flexible installation.

Section I: Specifications

General

• Semi-conductors: Transistors (38), FET (4), IC (27), Diode (49)
• Frequency Coverage: 144.000 ~ 146.000MHz (25KHz steps)
• Memory Channels: 3, programmable in-band frequencies
• Usable Conditions: Temperature: -10°C to 60°C (14°F to 140°F); Continuous operation
• Frequency Stability: Within ±1.5KHz
• Antenna Impedance: 50 ohms unbalanced
• Power Supply Requirement: 13.8V DC ±15% (negative ground), 3.0A Max.
• Current Drain: Transmitting: HIGH (10W) Approx. 2.5A, LOW (1W) Approx. 1.2A; Receiving: At max audio output Approx. 0.7A, Squelched Approx. 0.5A
• Dimensions: 156mm (W) x 58mm (H) x 228mm (D)
• Weight: Approx. 2.2kg

Transmitter

• Output Power: 10W (HIGH), 1W (LOW)
• Emission Mode: 16F3
• Modulation System: Variable reactance frequency modulation
• Max. Frequency Deviation: ±5KHz
• Spurious Emission: More than 60dB below carrier
• Microphone: 600 ohms dynamic microphone with push-to-talk switch (IC-SM2 electret condenser microphone may also be used.)
• Operating Mode: Simplex, Duplex (±600KHz from receive frequency)

Receiver

• Receiving System: Double-conversion superheterodyne
• Modulation Acceptance: 16F3
• Intermediate Frequency: 1st: 10.695MHz, 2nd: 455KHz
• Sensitivity: More than 30dB S+N/D/N+D at 1µV; Less than 0.6µV for 20dB Noise quieting
• Squelch Sensitivity: Less than 0.4µV
• Spurious Response Rejection Ratio: More than 60dB
• Selectivity: More than ±7.5KHz at -6dB point; Less than ±15KHz at -60dB point
• Audio Output Power: More than 2.0W
• Audio Output Impedance: 8 ohms

Section II: Description

Use of Microcomputer

The IC-280E is the world's first amateur transceiver with a P-channel MOS 4-bit microcomputer. It handles frequency control, band-edge detection, and display. The 3-channel memory is electrically controlled using a 256-bit RAM area, offering capabilities equivalent to conventional circuits with numerous C-MOS MSI's.

Separable Control Unit

The control portion (front panel) can be detached from the main unit and connected via a cable. This allows for flexible mounting, as the control unit is approximately one-third of the total size.

Superior Receiving Characteristics

Newly developed low-noise, large dynamic range junction FETs for the RF amplifier and first mixer, combined with helical cavity filters, provide excellent sensitivity and intermodulation distortion characteristics. High-quality monolithic crystal filters ensure stable receiving and durability.

Highly Stable Transmitting Characteristics

The transceiver uses a directly amplified VCO output without multipliers or mixers, and a power module in the PA unit to produce clean signals with minimal spurious radiation. RF power is selectable between 10W (HIGH) and 1W (LOW).

Section III: Installation

Unpacking

Carefully remove the transceiver from its packing carton and check for shipping damage. Notify the carrier or dealer immediately if damage is found. Retain shipping cartons for future storage, moving, or reshipment. Accessory hardware and cables are included.

Accessory Hardware List:

• 1. Microphone (dynamic type)
• 2. Microphone hook
• 3. Power cord
• 4. Spare fuses (5A)
• 5. Installing holder A
• 6. Installing holder B
• 7. Installing angle joint
• 8. Gimp screws
• 9. Flat washers
• 10. Plug for speaker
• 11. Mounting screws
• 12. Screws for additional bracket
• 13. Flat head screw's nuts
• 14. Mounting screw's nuts

Location

The transceiver can be placed in a car based on convenience and accessibility. The mobile mounting bracket provides guidance. Metal screws, bolts, or pop-rivets can be used for mounting. For fixed station use, a 3-amp power supply is recommended.

Power Requirements

The transceiver operates from a regulated 13.8V DC, 3-ampere negative ground source, such as a standard automobile 12V system. Ensure the vehicle's electrical system is in good condition (battery, generator/alternator, voltage regulator) to avoid operational issues. If using an AC power supply, ensure it is adequately regulated. Low voltage under load will impair performance.

CAUTION: Excessive Voltage (above 15VDC) will damage the transceiver. Verify source voltage before connecting.

The included DC power cable has a Red wire for positive (+) and a Black wire for negative (-). For mobile installations, direct connection to the battery terminals is recommended to minimize noise. If not possible, connect to a convenient B+ lead and the negative frame. The unit operates on a negative ground system only.

For use with a matching ICOM AC power supply, the DC power cable plugs into the transceiver, and the AC line cord plugs into a wall receptacle.

Antenna

A good, high-quality, 50-ohm impedance gain antenna is recommended for optimal performance. For VHF and low bands, every watt of ERP is significant. Investing in a gain antenna is worthwhile. Follow the manufacturer's instructions for antenna adjustment. Use an in-line watt meter (e.g., Drake WV-4, Bird Model 43) for VHF applications, as diode VSWR meters can be inaccurate. For mobile antennas, run the vehicle's motor at normal idling speed or higher during adjustment to ensure proper voltage.

The RF coaxial connector on the rear chassis is a standard PL-259 type.

Microphone

A high-quality dynamic microphone (600 ohms) is supplied. Plug it into the front panel receptacle. If using a different microphone, ensure it is approximately 600 ohms and wire it carefully, as the internal switching system depends on correct wiring.

External Speaker

An external speaker jack is provided. The external speaker impedance should be 8 ohms. Using an external speaker disables the internal speaker. An 8-ohm headset can also be used.

Section IV: Control Functions

Front Panel Controls and Indicators:

1. Transmit Indicator: Illuminates when transmitting.
2. Receive Indicator: Illuminates when receiving (and squelch is open).
3. Duplex/Simplex Switch: Selects Duplex or Simplex operation.
4. Duplex Mode Select Switch: Sets transmitting frequency 600KHz above or below receiving frequency in Duplex mode.
5. Memory-Write Switch: Used to program frequencies into memory channels.
6. Memory Channel Switch: Selects operation via tuning control ('D' position) or memory channels (1, 2, or 3).
7. Meter: Functions as a signal strength meter (S-meter) and relative RF output meter.
8. Tuning Control: Sets the operating frequency in 25KHz steps. Has 50 positions per turn.
9. Tone Call Button: Activates the 1750Hz tone-burst for repeater access.
10. VOL Control and Power ON/OFF Switch: Controls audio level and turns the unit ON/OFF.
11. SQL Control and High/Low Power Switch: Controls squelch threshold and sets RF output power (10W HIGH, 1W LOW). Pulling the knob selects LOW power.
12. MIC Connector: Accepts microphone plug.
13. Frequency Display: Digitally displays the operating frequency (1MHz, 100KHz, 10KHz digits, with a 5KHz indicator).

Back Panel Connectors:

14. Antenna Connector: Standard PL-259 coaxial connector.
15. Power Connector: Mates with DC cord plug.

Control Instructions:

• Duplex/Simplex Select Switch: Depress to lock for Duplex, release for Simplex.
• Duplex Mode Select Switch: For repeaters, set transmitting frequency 600KHz below (normal) or above receiving frequency. Non-functional in Simplex mode.
• Memory-Write Switch: With Memory Channel switch set to 'D', tune to desired frequency, then set Memory Channel switch to 1, 2, or 3 and press M-Write. This erases and programs the frequency.
• Memory Channel Switch: Selects 'D' (tuning control) or memory channels 1, 2, or 3.
• Meter: Displays signal strength (S1-S9, 20-60dB over S9) and relative RF output. Switches automatically between functions during T/R.
• Tuning Control: Sets operating frequency in 25KHz steps.
• Tone Call Button: Depress during transmit for a 1750Hz tone-burst to access repeaters. Duration varies (100mS to 2S).
• VOL Control and Power ON/OFF Switch: Turn fully CCW for OFF. Turn CW beyond the click to turn ON and adjust audio level.
• SQL Control and High/Low Power Switch: Turn CW to increase squelch threshold. Turn fully CCW to disable squelch. Pull knob for 1W LOW power; push in for 10W HIGH power.
• Frequency Display: Shows operating frequency.

Section V: Operation

Initial Preparations

1. Ensure VOL Control/Power Switch is OFF.
2. Connect power supply cord to the power connector. Red lead to positive, black to negative. Incorrect polarity will blow the fuse.
3. Connect microphone to MIC Connector.
4. Connect antenna to Antenna Connector (ensure 50-ohm impedance, not shorted/open).
5. Set Squelch control fully counter-clockwise.

Receiving

1. Set Memory Channel Switch to 'D' position.
2. Set SQL Control to fully CCW.
3. Turn VOL control CW (it will click ON). The display will show "5.00" (for 145.00MHz).
4. Turn VOL control CW to a comfortable audio level.
5. If only noise is heard, turn SQL control CW until noise stops, then set just below that threshold.
6. Turn Tuning Control to the desired frequency.

Transmitting

1. Set Duplex/Simplex Switch: SIMPLEX for simplex operation (Duplex Mode Switch non-functional). DUPLEX for repeater operation.
2. Set Duplex Mode Switch: For repeater operation, select 600KHz above or below receiving frequency (600KHz below is normal).
3. Set Tuning Control to the desired frequency.
4. Set SQL Control/High/Low Power Switch to HIGH (normal position).
5. If lower output power is sufficient, set to LOW (out position).
6. Depress PTT switch on microphone to transmit; release to receive. Speak at a normal level.
7. Depress Tone Call Button for repeater access if needed.

Programming the Memory Channels

Perform these steps in receive mode:

1. Set Memory Channel Switch to 'D' position.
2. Turn Tuning Control to set the desired frequency on the Frequency Display.
3. Set Memory Channel Switch to the desired channel (1, 2, or 3). The display shows "5.00" if unprogrammed, or the existing frequency.
4. Depress Memory-Write Switch. The Frequency Display shows the tuned frequency, cancelling "5.00" or the previous frequency.

Repeat for the other two memory channels. You can then operate using the Tuning Control or the programmed channels.

Section VI: Inside View

The top view of the main unit reveals numerous components including:

• Integrated Circuits (ICs): IC1 (PA module), IC2 (2nd IF limiter), IC3 (Squelch control/Micro processor), IC4 (Squelch control), IC5 (APC Control), IC7 (Micro processor), IC9 (TP4370A), IC11 (Mic amp).
• Transistors (Q2, Q7).
• Resistors (R26, R34, R43, R45, R52, R64, R70) for adjustments.
• Filters (Spurious filter, FL1, FL3).
• Helical cavities (L1-5).
• Ceramic discriminator (DS1).
• Tone Call Unit.
• Crystal (X1).
• Various other components like diodes and capacitors.

Section VII: Theory of Operation

General

The IC-280E utilizes a digital Phase Locked Loop (PLL) circuit for its local oscillator, controlled by a microcomputer. This system manages band edges, memory channels, and duplex settings. Received signals are mixed with the PLL output, converted to IF signals (10.695MHz, then 455KHz), amplified, and demodulated by a ceramic discriminator.

In transmit mode, the PLL output is shifted to the transmit frequency, amplified to 10W by the PA module, and frequency modulation is achieved within the PLL circuit.

Receiving Unit

Antenna Switching Circuit

The antenna connector feeds signals through a low-pass filter to the antenna switching circuit. In receive mode, Q1 and diodes D1-D3 conduct RF signals to the RF amplifier circuit.

RF Circuit

Signals are filtered by two-stage helical cavity filters to reduce interference and intermodulation. Q2 amplifies these signals, which are then fed to the first mixer (Q3). Q3 mixes the input with the local oscillator signal from the PLL to produce the first IF (10.695MHz). A low-noise junction FET is used for the RF amplifier and first mixer to ensure good cross-modulation and desensitization.

IF Circuit

IF signals from Q3 are filtered by a crystal filter and fed to the second mixer (Q4). The PLL's reference frequency signal acts as the local oscillator for Q4. Signals are converted to 455KHz, amplified by IC1 (approx. 50dB) after passing through a ceramic filter, and then further amplified by Q5 (variable amplification).

The S-meter uses detectors (D7/D20 and D5/D6) to measure signal strength. The audio signals are amplified by IC2 (approx. 60dB limiting amplification) and demodulated by a circuit including ceramic discriminator DS1 and diodes D8-D9.

AF Circuit

Demodulated audio signals pass through a de-emphasis circuit. An attenuator element (IC4-1) controlled by the SQL circuit switches audio signals ON/OFF. The output is fed to the control unit.

SQL Circuit

Signals from the demodulator are filtered to isolate approximately 20KHz noise. The SQL control voltage adjusts the noise level. Amplified noise signals are fed to a comparator (IC3-2) and detected. This detected signal switches audio signals via Q6 and IC4-1.

Transmitting Unit

PA Circuit

FM signals from the PLL circuit (approx. 200mW) are fed to the IC1 PA module for amplification up to 10W. A 3-stage low-pass filter removes unwanted harmonics.

APC Circuit

This circuit maintains constant RF output power (10W or 1W) despite variations in power supply voltage or antenna load. It uses IC7 and Q1 to control the PA driver's power voltage. IC5-1 and IC5-2 operate for High/Low power modes, with R52 and R64 adjusting detection levels. The circuit protects the PA module from improper loads. D4 rectifies RF signals for the RF output meter, adjusted by R34.

Others

• Transmit Indicator Circuit: An LED illuminates when transmitting, controlled by the PTT switch.
• Receive Indicator Circuit: An LED illuminates when receiving and squelch is open, controlled by the Squelch circuit via a switching transistor.

Section VII: Theory of Operation (Continued)

Power Circuit

The main unit includes 9V regulators (Q7, Q8) to provide stable voltage. Q7 regulates voltage for the PLL unit. Q8 provides a 9V receive mode regulator for the main unit. During transmit, Q8 is turned OFF to save power.

PLL Unit

In transmit mode, the PLL circuit generates the transmit frequency and modulates the VCO for FM. In receive mode, it oscillates at 10.695MHz below the desired receive frequency.

Local Oscillator Circuit

Crystals X1 (45.997MHz transmit) and X2 (42.432MHz receive) are selected by Q1 and multiplied by Q3. Q2, Q15, C102, and C103 form a circuit that shifts frequencies by 5KHz.

Mixer and Amplifier Circuit

The local oscillator signal is mixed with the VCO output by IC2. The mixed signal is filtered by a low-pass filter (L6, C20-C22) and amplified by IC1 and Q5.

Reference Oscillator Circuit

A 10.24MHz signal from Q9 is divided by IC5 to produce 10KHz for the PLL's phase reference. The 10.24MHz signal is also used for the second mixer.

Frequency Divider Circuit

Q12, IC3, and IC6 divide the mixed frequency based on data from the driver unit.

Phase Detector and Loop-Filter Circuit

The phase detector (IC4) generates pulses based on the 10KHz reference and the frequency divider output. A loop filter (R20-22, C72-C73, C31) smooths these pulses, providing voltage to lock the VCO frequency.

VCO Circuit

Q8 is the oscillator and Q9 is a buffer. In transmit, the VCO signal is frequency modulated by audio signals via varicap D8. In receive, the frequency is shifted down by the IF frequency value.

Buffer and Pre-driver Circuit

Q9, Q10, Q11, and Q14 act as buffers for the VCO. The VCO range is approximately 19MHz, requiring wide passband buffers. Buffer power is turned OFF when not needed.

Other Circuits

The PLL unit includes a microphone amplifier circuit (Q13). Q4 monitors for PLL lock failure and prevents undesired radiation.

Driver Unit

Up Down Detector Circuit

A 90-degree phase signal from a photo-interrupter (IC1/IC2) and chopper disc is latched by IC4/IC5. This signal synchronizes with the CPU's RO signal and controls IC6, feeding data to the CPU (K1, K2, K4, K8) for UP/DOWN control of frequency.

The CPU presets the frequency (e.g., 145.00MHz) and uses the dial rotation sensor data to add or subtract from this preset frequency.

Display Latch Circuit

The CPU sends divide ratio data to the frequency display and PLL divider for time-sharing operation.

Pulse signals from the CPU synchronize with 7-segment display data. Q1, Q2, Q3 control the 1MHz, 100KHz, and 10KHz LEDs respectively. Q4 and Q5 prevent incorrect data feeding. The 5KHz display LED indicates 5KHz step operation.

MIC AMP and Audio AMP

IC11 acts as a dual low-noise op-amp for microphone amplification and audio limiting. IC10 is a high-power audio amplifier (2W+). Q14 mutes IC10 during transmit.

Power Supply Circuit

A voltage regulator circuit protects the CPU and other components from voltage fluctuations. It uses Zener diodes (D6, D4) and transistors (Q10, Q7, Q6) to maintain stable voltages (9V, 5.5V). If the main supply drops below ~10V, a protection circuit activates.

Tone Call Unit

This unit generates a 1750Hz tone-burst for repeater access. IC1 acts as a multivibrator. The tone-burst frequency is adjustable by R2, and output level by R4.

Section VIII: Troubleshooting

This chart helps resolve common issues not related to equipment malfunction. Contact a dealer or ICOM distributor if problems persist.

Section IX: Voltage Charts

NOTE: Measuring instrument is a 50K Ω/V multimeter.

MAIN UNIT TRANSISTORS

MAIN UNIT IC IN TRANSMIT MODE

MAIN UNIT IC IN RECEIVE MODE

Section IX: Voltage Charts (Continued)

PLL UNIT TRANSISTORS

PLL UNIT IC

DRIVER UNIT TRANSISTORS

Section IX: Voltage Charts (Continued)

DRIVER UNIT TRANSISTORS (Continued)

DRIVER UNIT IC IN TRANSMIT MODE

DRIVER UNIT IC IN RECEIVE MODE

Section X: Block Diagram

The block diagram illustrates the transceiver's architecture:

• Inputs: Antenna, Microphone, Power (DC 13.8V), Memory power supply.
• Signal Path (Receive): Antenna -> Antenna Switch (Q1, D1-3) -> RF Amplifier (Q2) -> Helical Cavity Filter -> 1st Mixer (Q3) -> Crystal Filter -> 2nd Mixer (Q4) -> 2nd IF Amp/Limiter (IC1, IC2) -> Ceramic Filter -> Ceramic Discriminator (DS1, D8-9) -> AF Amplifier (IC4-1) -> Volume Control (VOL) -> AF Power Amplifier (IC10) -> Speaker.
• Signal Path (Transmit): Microphone -> AF Amplifier (IC11) -> Modulator (D8) -> VCO -> PLL Unit -> Driver (Q10, Q11) -> Power Amplifier (IC1) -> Harmonics Filter -> Antenna.
• Control & Frequency Generation: CPU (IC7) controls Memory Channel Switch, UP/DOWN Control, TUNE, Mode Control. PLL Unit generates frequencies using VCO, Local Oscillator (X1, X2), Reference Oscillator (Q9), Frequency Divider (IC5), Phase Detector (IC4), Loop Filter.
• Ancillary Circuits: Squelch Control (SQL), S-Meter Detector, Tone Oscillator (IC1), APC Control (IC5, R52, R64), Voltage Regulators (Q7, Q8), Reverse Polarity Protector (D10).
• Indicators: Transmit Indicator LED, Receive Indicator LED, Frequency Display (IC12-14), 5KHz Display LED.
• Outputs: Speaker, Antenna.

Section XI: Options

ICOM offers a variety of options to enhance the use of the IC-280E:

• REMOTE CABLE KIT FOR IC-280E: Allows for remote operation.
• DC POWER CORD WITH MEMORY BACKUP POWER PLUG: Provides power and maintains memory settings.
• IC-3PE POWER SUPPLY: A 13.8V, 3A power supply.
• IC-SM2 DESK MICROPHONE: An electret condenser type desk microphone.
• MOBILE MOUNTING BRACKET (F) FOR IC-280E: For secure installation in vehicles.

MEMO

Blank page for notes.