ICOM IC-751 HF All Band Transceiver General Coverage Receiver

SECTION 1 SPECIFICATIONS

GENERAL

Number of Semiconductors: Transistors: 105, FET: 16, IC (Includes CPU): 51, Diodes: 219

Frequency Coverage:
Ham Band: 1.8 MHz~2.0MHz, 3.45MHz~4.1MHz, 6.95MHz~7.5MHz, 9.95MHz~10.5MHz, 13.95MHz~14.5MHz, 17.95MHz~18.5MHz, 20.95MHz~21.5MHz, 24.45MHz ~25.1MHz, 27.95MHz~30.0MHz
General Cover (Receive Only): 0.1MHz~30.0MHz (Thirty 1MHz Segments or Continuous)

RIT/XIT Coverage: ±9.9KHz

Frequency Control: CPU based 10Hz step Digital PLL synthesizer. Independent Transmit-Receive Frequency Available on same band.

Frequency Readout: 6 digit 100Hz readout.

Frequency Stability: Less than ±200Hz after switch on 1 min to 60 mins, and less than ±30Hz after 1 hour. Less than ±500Hz in the range of 0°C~+50°C.

Power Supply Requirements: DC 13.8V ±15% Negative ground. Current drain 20A max. (at 200W input). AC power supply is available for AC operation.

Antenna Impedance: 50 ohms Unbalanced

Weight: 8.5Kg

Dimensions: 115mm(H) x 306mm(W) x 355mm(D)

Harmonic Output: More than 40dB below peak power output

Spurious Output: More than 60dB below peak power output

Carrier Suppression: More than 40dB below peak power output

Unwanted Sideband: More than 55dB down at 1000Hz AF input

Microphone: Impedance 600 ohms, Input Level 12 millivolts typical. Dynamic or Electret Condenser Microphone (Optional IC-HM12 or IC-SM6 can be used.)

TRANSMITTER

RF Power: SSB (A3J): 200 Watts PEP input; CW (A1), RTTY (F1): 200 Watts input; FM (F3): 40 Watts output; AM (A3): Continuously Adjustable Output power 10 Watts ~ Max.

Emission Mode: A3J (SSB: Upper sideband and Lower sideband), A1 (CW), F1 (RTTY: Frequency Shift Keying), A3 (AM), F3 (FM)

RECEIVER

Receiving System: SSB, CW, RTTY, AM, FM Quadruple Conversion Superheterodyne with continuous Bandwidth Control. Triple Conversion Superheterodyne with continuous Bandwidth Control.

Receiving Mode: A1, A3J (USB, LSB) F₁ (Output FSK audio signal), A3, F3

IF Frequencies: 1st: 70.4515MHz, 2nd: 9.0115MHz (SSB), 9.0106MHz (CW, RTTY), 3rd: 9.0100MHz (AM, FM), 4th: 455KHz (except FM), 350KHz (except FM)

Sensitivity:
SSB, CW, RTTY: 0.1~0.5MHz Less than 0.5µV for 10dB S/N; 0.5~1.6MHz Less than 1.0µV for 10dB S/N; 1.6~30MHz Less than 0.15µV for 10dB S/N.
AM: 0.1~0.5MHz Less than 3µV for 10dB S/N; 0.5~1.6MHz Less than 6µV for 10dB S/N; 1.6~30MHz Less than 1µV for 10dB S/N.
FM: 1.6~30MHz Less than 3µV for 12dB SINAD.

Squelch Sensitivity: 1.6~30MHz Less than 0.3µV

Selectivity: SSB, CW, RTTY: ±1.15KHz (Adjustable to ±0.4KHz Min) at -6dB; ±2.0KHz at -60dB. AM: ±1.2KHz at -6dB, ±2.25KHz at -60dB (When Filter switch ON). FM: ±2.0KHz at -6dB, ±7.5KHz at -60dB; ±7.5KHz at -6dB, ±15KHz at -60dB.

Notch Filter Attenuation: More than 45dB

Spurious Response Rejection Ratio: More than 60dB

Audio Output: More than 3 Watts

Audio Output Impedance: 8 ohms

Specifications are approximate and are subject to change without notice or obligation.

SECTION 2 FEATURES

ALL BAND, ALL MODE, ALL SOLID-STATE: The IC-751 covers all Amateur HF frequencies from 1.8MHz to 29.9999MHz, including the new three bands of 10MHz, 18MHz and 24MHz. It offers not only SSB, but also CW, AM, FM and RTTY. All circuits are solid-state, providing about 100 watts output.

GENERAL COVERAGE RECEIVER CAPABILITY: The IC-751 functions as an all amateur band transceiver and a general coverage receiver between 100KHz and 30MHz with continuous tuning. An Up-conversion system using a high side IF and Microcomputer Control System enables these capabilities. Low-pass filters and band-pass filters are selected by electric signal from the CPU for a no tune-up system.

DUAL VFO: Dual VFOs controlled by a large tuning knob allow easy access to split frequencies used in DX operation. Normal tuning rate is in 10Hz increments, increasing with knob rotation to 100Hz increments. A tuning speed button provides 1KHz tuning. Digital outputs are available for computer control of frequency and functions, and for synthesized voice frequency readout.

32 MEMORIES: Thirty-two tunable memories store mode, HAM/GENERAL COVERAGE mode, and frequency. The RAM is backed up by an internal lithium battery for up to seven years. Scanning of frequencies, memories, and bands is possible from the unit or the optional scanning microphone. Data can be transferred between VFOs and memories.

OUTSTANDING RECEIVER PERFORMANCE: Features an ICOM-developed J-FET DBM with a 105dB dynamic range. The 70.4515MHz first IF virtually eliminates spurious responses. A high gain 9.0115MHz second IF with ICOM's PBT selectivity, a deep IF notch filter, adjustable AGC, noise blanker, audio tone control, and RIT with separate readout provide clear reception even in strong QRM or high noise levels. A low noise receiver preamp provides exceptional sensitivity.

TRANSMITTER: Features high reliability transistors with low IMD (-32dB @ 100W), full 100% duty cycle (internal cooling fan standard), 12 volt DC design. Includes quiet relay selection of transmitter LPFs, transmit audio tone control, monitor circuit, XIT, and a high performance speech processor. For CW operators, semi break-in or full QSK is provided.

OTHER FEATURES: Includes full function metering, SSB and FM squelch, convenient large controls, a selection of plug-in filters, and a high visibility multi-color fluorescent display showing frequency in white and other functions in white or red.

SECTION 3 INSTALLATION

BE SURE TO READ THE FOLLOWING INSTRUCTIONS CAREFULLY BEFORE OPERATION

3-1 UNPACKING

Carefully remove the transceiver from the packing carton and examine it for shipping damage. Notify the carrier or dealer immediately if damage is apparent. Keep shipping cartons for storage, moving, or reshipment. Accessory cables and plugs are packed with the transceiver.

Included Accessories:

• 1. DC Power Cord
• 2. Pin Plugs
• 3. External Speaker Plug
• 4. Spare Fuses (20 Amp)
• 5. Spare Fuses (3 Amp)
• 6. Key Plug

3-2 RECOMMENDATIONS FOR INSTALLATION

1. Avoid direct sunlight, high temperature, dusty, or humid places.
2. Ensure at least 1 inch (3cm) clearance around the unit for ventilation. Do not obstruct the rear PA heatsink. Avoid places near heaters or air conditioners.
3. Position the unit for easy access to controls and clear visibility of the frequency indication and meter.
4. For mobile installation, use an optional mounting bracket in a secure location that does not interfere with driving.
5. Use the Ground Lug!

3-3 POWER SUPPLY

For AC operation, use the special power supply IC-PS15, or optional built-in power supply IC-PS35. For DC operation, use a car battery or other DC power supply with 12-15 Volts and at least 20 Amps current capacity. Note that transmission current consumption is 16-20 Amps. Ensure the battery and electrical system are in good condition.

DC Power Cord Connection: Ensure the power switch is OFF and T/R switch is in RECEIVE. Connect the RED lead to the positive terminal and the BLACK lead to the negative terminal of the DC power supply. (Reverse connection will blow the fuse.) Connect the DC plug to the IC-751 rear panel socket.

Diagram Description: A diagram shows the connection of the DC power cord to the IC-751, IC-PS15 (for AC operation), and a DC power source (battery) with fuse.

3-4 ANTENNA

Antennas are critical for performance. Use a high-performance antenna suited to your desired frequency bands with a 50-ohm impedance feeder cable. Ensure connectors are in good condition. Connect whip antenna ground terminals to the car body. Avoid transmitting under mismatched conditions to prevent overloading the final stage. For general coverage reception, a long-wire antenna and antenna coupler are recommended. The antenna impedance should be 50 ohms.

3-5 GROUND

Connect a heavy, short ground wire from a good earth point to the rear panel ground terminal to prevent electrical shock, TVI, and BCI.

3-6 MICROPHONE

Use the optional electret condenser hand microphone IC-HM12 or stand microphone IC-SM6 by plugging into the front panel receptacle. If using a different microphone, ensure it has the proper output level and wire it correctly. Refer to schematics on page 4 for hookup details.

Diagram Description: Exploded view of microphone plug and wiring diagrams for IC-HM12 and IC-SM6 are shown.

3-8 CW KEY

Connect a key to the KEY jack on the rear panel using a 1/4-inch standard plug. The diagram shows the plug connection.

Diagram Description: A simple wiring diagram for a CW key plug shows (+) and (-) terminals.

3-8 RTTY

Connect the ACC socket pins 8 (ground) and 9 to your tele-typewriter via a high-speed relay or TTL level converter. AF output is available from pin 4. Refer to 5-7 RTTY OPERATION for details.

3-9 EXTERNAL SPEAKER

Use the EXTERNAL SPEAKER jack on the rear panel for an external speaker. The impedance should be 8 ohms. The internal speaker is disabled when an external speaker is connected.

3-10 HEADPHONES

Use standard 4-16 ohm headphones. Inserting the plug halfway allows both headphone and speaker to operate. Full insertion disables the speaker.

3-11 COOLING FAN

The PA unit has a cooling fan that activates when the temperature rises to approximately 50°C to provide additional cooling. If the temperature reaches a danger limit (90°C), the fan runs faster, and output power is reduced to 50 Watts. Investigate overheating causes (e.g., antenna mismatch) immediately.

SECTION 4 OPERATING CONTROLS

4-1 FRONT PANEL

The front panel features numerous controls and indicators. Key controls include:

• MULTI-FUNCTION METER (39): Displays various parameters.
• MODE SELECT SWITCHES (38): Selects AM, FM, CW, SSB, RTTY modes.
• FUNCTION KEY (36) & INDICATOR (37): Activates secondary functions.
• NB LEVEL CONTROL (35), NB TIMING SWITCH (32), MONITOR SWITCH (31), COMP SWITCH (30): Noise blanker, monitor, and speech processor controls.
• VOX GAIN CONTROL (33), VOX DELAY CONTROL (34): Controls for voice-activated transmit/receive.
• POWER SWITCH: Turns the unit ON/OFF.
• AGC SWITCH (5): Selects AGC time constant (SLOW/FAST/OFF).
• T/R SWITCH (2): Manually switches between Transmit and Receive.
• METER SWITCH (6): Selects meter function (Vc, Ic, COMP, ALC, Po).
• MIC CONNECTOR (3): For microphone input.
• PHONES JACK (4): For headphone connection.
• AF GAIN CONTROL (7), RF GAIN CONTROL (8): Audio and RF gain adjustments.
• HAM/GENERAL COVER SELECT SWITCH (13): Selects operating band mode.
• SQUELCH CONTROL (9), TONE CONTROL (10): Squelch and audio tone adjustments.
• SPEECH SYNTHESIZER SWITCH: Activates optional speech synthesizer.
• MODE SELECTIVE SCAN SWITCH: For mode-specific scanning.
• MIC GAIN CONTROL (11): Microphone gain adjustment.
• RF POWER CONTROL (12): Adjusts RF output power.
• SCAN START/STOP BUTTON (16): Controls scanning functions.
• DIAL LOCK SWITCH (17): Locks the tuning control.
• TUNING CONTROL (18): Main frequency tuning knob.
• TUNING RATE SWITCH (19): Selects tuning step (10Hz, 50Hz, 1KHz).
• DIAL FUNCTION SELECT SWITCH (20): Changes dial function (VFO/Memory).
• BAND SELECT FUNCTION SWITCH (21): Selects operating band.
• INCREMENTAL TUNING CONTROL (22): Fine-tunes receive/transmit frequency (RIT/XIT).
• RIT SWITCH (23), XIT SWITCH (24): Activates Receiver/Transmitter Incremental Tuning.
• RIT/XIT CLEAR BUTTON (25): Clears RIT/XIT shift.
• FILTER SWITCH (26): Selects IF filters for selectivity.
• NOTCH FILTER SWITCH (27): Activates notch filter.
• P.B. TUNE (PASS BAND TUNING) CONTROL (28): Adjusts pass-band width.
• NOTCH FILTER CONTROL (29): Adjusts notch filter frequency.
• TRANSMIT INDICATOR (40), RECEIVE INDICATOR (41), NARROW INDICATOR (42): Status indicators.
• FREQUENCY DISPLAY (43): Shows frequency, mode, VFO/Memory status, RIT/XIT status, SCAN, DUPLEX, HAM/GENE mode.
• VFO SWITCH (44): Selects VFO A or VFO B.
• VFO EQUALIZING SWITCH (45): Copies VFO settings.
• DUPLEX (SPLIT) SWITCH (46): Enables split frequency operation.
• VFO/MEMORY SWITCH (47): Switches between VFO and Memory modes.
• MEMORY WRITE BUTTON (48): Stores settings into memory.
• FREQUENCY TRANSFER BUTTON (49): Transfers memory contents to VFO.

4-2 TOP COVER

Controls on the top cover include:

• PREAMP/ATT SWITCH (50): Selects RF preamplifier or attenuator.
• MARKER SWITCH (51): Turns the marker circuit ON/OFF.
• ANTI-VOX CONTROL (52): Adjusts anti-VOX level.
• MONITOR LEVEL CONTROL (53): Adjusts monitor audio level.
• MARKER CALIBRATOR (54): Calibrates marker frequency.

4-3 REAR PANEL CONNECTIONS

Rear panel connections include:

• 55 ANTENNA (ANT) CONNECTOR: 50 ohm impedance, PL-259 connector.
• 56 KEY JACK: For CW key connection (1/4 inch plug).
• 57 EXTERNAL SPEAKER JACK: For 8 ohm external speaker.
• 58 EXTERNAL ALC TERMINAL: Input for external ALC signal.
• 59 T/R CONTROL TERMINAL: Controls external linear amplifier or transverter (24V 1A DC).
• 60 RECEIVER INPUT TERMINAL: Direct receiver input.
• 61 RECEIVER ANTENNA OUTPUT TERMINAL: Output for received signals.
• 62 SPARE TERMINAL: For personal use.
• 63 TRANSVERTER TERMINAL: For VHF/UHF transverter connection.
• 64 GROUND TERMINAL: For grounding the equipment.
• 65 DC POWER SOCKET: For DC power connection.
• 66 ACCESSORY (ACC) SOCKET: Provides various functions (modulation output, receiver output, T/R changeover, etc.). Details provided in a table.
• 67 OPTIONAL INTERFACE UNIT CONNECTOR POSITION: For DP-25 connector.
• 68 OPTIONAL BUILT-IN AC POWER SUPPLY SOCKET POSITION: For IC-PS35 connection.

SECTION 5 OPERATING INSTRUCTIONS

5-1 HOW TO TUNE

Follow these instructions for tuning in any mode for optimum operation.

5-1-1 PRESET

When powered ON, the frequency display shows frequency, HAM/GENE mode, VFO A, and memory channel 01. RIT/XIT, DUPLEX, and SCAN are OFF.

5-1-2 HAM BAND/GENERAL COVERAGE SELECTION

Pushing the HAM/GENERAL COVER SELECT switch alternates between HAM BAND mode (nine amateur bands 1.8-28MHz) and GENERAL COVERAGE mode (0.1-30MHz receiver only). Mode changes retain the frequency. If switching from GENERAL COVERAGE to HAM BAND and the previous frequency was not a HAM band, it initializes to 1.900.0MHz.

5-1-3 BAND SWITCHING

Push the BAND SELECT FUNCTION switch and rotate the TUNING CONTROL to change bands. In HAM BAND mode, clockwise moves to the next upper band, counterclockwise to the next lower band, initializing frequency. In GENERAL COVERAGE mode, clockwise adds 1MHz, counterclockwise subtracts 1MHz, maintaining lower digits. Band limits wrap around.

Diagram Description: A table lists HAM bands and their corresponding frequency ranges for LSB, AM-FM, CW, RTTY, and USB modes.

5-1-4 FREQUENCY DISPLAY ON EACH MODE

The display shows carrier frequency. Frequency shifts for different modes (USB, LSB, CW, RTTY, FM, AM) are automatically handled. A diagram illustrates frequency differences between modes.

In the HAM BAND SSB mode, LSB is used for 1.8, 3.5, 7MHz bands, and USB for 10MHz and above. Push FUNCTION KEY then SSB switch for opposite sideband.

5-1-5 TUNING CONTROL

Rotating the TUNING CONTROL clockwise increases frequency, counterclockwise decreases it in 10Hz steps. Faster rotation selects 100Hz steps. Pushing the TUNING RATE SWITCH selects 1KHz steps, clearing the 100Hz digit to "0".

The frequency range for each HAM band is shown in a table. In GENERAL COVERAGE mode, continuous rotation moves through MHz ranges.

5-1-6 DIAL LOCK SWITCH

Pushing this switch locks the VFO at the displayed frequency, disabling the tuning control. Push again to disengage.

5-1-7 VFO SWITCH

The IC-751 has two VFOs (VFO A and VFO B) for receiving and transmitting. Pushing the VFO switch selects between them. Switching VFOs does not clear the other VFO's frequency, mode, or HAM/GENE setting.

Example: Setting VFO A to 14.257MHz USB. Pushing VFO switch selects VFO B. Later, pushing again returns to VFO A showing 14.257.0 USB. This allows setting one VFO for operation and the other for searching.

5-1-8 DUPLEX (SPLIT) SWITCH

This switch changes the relationship of the two VFOs. When OFF, one VFO is for both receive and transmit. When ON, the letters "DUP" appear, and one VFO is for receive, the other for transmit, enabling split frequency operation.

Example: Set VFO A to 7.057MHz (Receive) and VFO B to 7.255MHz (Transmit). Push DUPLEX switch ON. The display shows 7.057MHz for receive and 7.255MHz for transmit.

Each VFO stores its mode. Cross-mode QSOs are possible.

5-1-9 TRANSFERRING VFO FREQUENCY

The VFO EQUALIZING switch copies the frequency, mode, and HAM/GENE setting from one VFO to the other. This allows setting one VFO for a specific frequency and using the other for band searching.

5-1-10 RIT (RECEIVE INCREMENTAL TUNING)

The RIT circuit shifts the receive frequency up to 9.9KHz without moving the transmit frequency. Push the RIT switch ON; "RIT" and shifted frequency appear. Use the INCREMENTAL TUNING CONTROL (10Hz steps) to adjust. Pushing RIT again turns it OFF, but the shifted frequency is stored. Push RIT/XIT CLEAR to reset the shift to "0.0". Pushing FUNCTION KEY then RIT/XIT CLEAR adds the shifted frequency to the displayed one.

5-1-11 XIT (TRANSMIT INCREMENTAL TUNING)

The XIT circuit shifts the transmit frequency up to 9.9KHz without moving the receive frequency. Push the XIT switch ON; "XIT" and shifted frequency appear. Use the INCREMENTAL TUNING CONTROL. If RIT was ON, XIT uses the stored RIT shift. Push RIT/XIT CLEAR to reset. Pushing FUNCTION KEY then RIT/XIT CLEAR adds the shifted frequency to the displayed one.

5-1-12 DIAL FUNCTION SELECT SWITCH (IN VFO MODE)

Pushing the DFS switch locks the VFO frequency. Turning the TUNING CONTROL changes the memory channel number. This is useful for memorizing frequencies/modes into memory. Push MEMORY WRITE to store. Push FREQUENCY TRANSFER to load memory contents to VFO.

5-2 MEMORY CHANNEL OPERATION

5-2-1 MEMORY CHANNEL SELECTION

When powered ON, the set starts in VFO A mode, memory channel "01". Pushing VFO/MEMORY switch enters MEMORY CHANNEL MODE, displaying contents of channel 1. The letters "MEMO" appear. Turning TUNING CONTROL cycles through memory channels (1-32). Channels without stored data show only MHz/KHz decimals but retain the previous frequency/mode.

5-2-2 DIAL FUNCTION SELECT SWITCH (IN MEMORY CHANNEL MODE)

In MEMORY CHANNEL MODE, pushing DFS locks the selected channel. Turning TUNING CONTROL changes the displayed frequency, allowing tuning or rewriting the memory. Push FREQUENCY TRANSFER to load memory contents to VFO.

5-2-3 MEMORY WRITE (PROGRAMMING THE MEMORY CHANNELS)

Set desired frequency, mode, and HAM/GENE mode using a VFO. Push DFS, then select a memory channel using TUNING CONTROL. Push VFO/MEMORY to check contents. Push MEMORY WRITE to store the displayed settings into the selected channel, overwriting previous data.

5-2-4 MEMORY CLEARING

To clear a memory channel: select the channel, push FUNCTION KEY, then MEMORY WRITE or FREQUENCY TRANSFER button. The channel contents will be cleared.

5-3 TUNING BY UP/DOWN BUTTONS ON THE MICROPHONE

5-3-1 FREQUENCY CONTROL

Pushing the UP or DN buttons on the optional microphone changes the frequency by one increment. Continuous pressing changes frequency similar to the TUNING CONTROL, at a rate set by the TUNING RATE SWITCH.

5-3-2 MEMORY CHANNEL SELECTING

In MEMORY CHANNEL mode, or when DFS is pushed in VFO mode, depressing UP or DN buttons on the microphone continuously changes the memory channel number every two seconds.

5-4 SCANNING OPERATION

The IC-751 offers various scanning operations.

5-4-1 MEMORY SCAN

Scans all programmed memory channels continuously from highest to lowest. Scan stops if SQUELCH opens on a signal, then restarts after a delay. Depress SCAN START/STOP to stop or restart.

5-4-2 MODE SELECTIVE SCAN

Scans only channels with the desired operating mode. Select a channel with the desired mode, push MODE SELECTIVE SCAN switch, then SCAN START/STOP button.

5-4-3 PROGRAMMED SCAN

Scans between two frequencies memorized in channels "1" and "2". Both channels must store the same operation mode (HAM BAND or GENERAL COVERAGE) and be in the same band. Scan starts from the higher frequency edge (channel 1 or 2) down to the lower edge, then loops. Scan stops if SQUELCH opens on a signal, monitoring for a set time before resuming. Depress SCAN START/STOP to clear scanning and return to normal VFO operation.

5-4-4 RESUMING SCAN

All scan modes have a resume function. If stopped by auto-stop (signal reception), the scan restarts after about 10 seconds.

5-5 SSB OPERATION

5-5-1 RECEIVING

Set controls as follows for SSB reception: POWER SWITCH OFF, T/R SWITCH RECEIVE, VOX GAIN/NB LEVEL/AGC/SQUELCH/TONE CONTROL to specified positions, TUNING RATE/DFS/BAND SELECT/DIAL LOCK/FILTER/NOTCH FILTER/DUPLEX/PREAMP/ATT SWITCH OFF. Push POWER switch ON. VFO A and memory channel "01" contents are displayed. LSB is typically used on lower bands (1.8-7MHz), USB on higher bands (10MHz+). Push FUNCTION KEY then SSB switch for opposite sideband. Push BAND SELECT FUNCTION switch and turn TUNING CONTROL to change bands. Slowly turn AF GAIN to a comfortable level. Tune with TUNING CONTROL for maximum signal strength and clearest audio. Adjust RF GAIN and TONE control. Set SQUELCH to cut noise.

5-5-2 NB (NOISE BLANKER)

For pulse noise (e.g., ignition), turn NB LEVEL clockwise to ON. WIDE position is effective for woodpecker noise. If receiving signal is too strong, noise blanker may affect it; set NB switch to OUT or turn NB LEVEL counterclockwise (OFF).

5-5-3 AGC (AUTOMATIC GAIN CONTROL)

The IC-751 has a fast attack/slow release AGC system. For normal SSB, use SLOW position. For fast fading or CW, use FAST position. Setting AGC to OFF disables the AGC circuit and S-meter.

5-5-4 PREAMP/ATT SWITCH

Use PRE position for weak signals to increase sensitivity. Use ATT position for strong nearby signals to reduce interference and improve stability. Leave in OFF for normal operation.

5-5-5 P.B. (PASS-BAND) TUNING

Narrows bandwidth (selectivity) up to 800Hz, effective for reducing interference. Center position is widest. For LSB, turn counterclockwise for higher frequency interference (high-pitched tones), clockwise for lower frequency interference (low-pitched tones). For USB, the opposite applies. Can also adjust audio tone.

5-5-6 FILTER SWITCH

Selects internal filter combinations for improved selectivity. Optional filters can be installed.

5-5-7 NOTCH FILTER

Notches a specific frequency in the IF pass-band to reduce interference like beat-tones. Push NOTCH FILTER switch ON and adjust NOTCH FILTER CONTROL.

5-5-8 TRANSMITTING

Before transmitting, check for clear channels. Use a dummy load for adjustment. Set MIC GAIN, RF POWER CONTROL, METER SWITCH, VOX GAIN CONTROL as specified. Speak into microphone; meter needle should stay within ALC zone at voice peaks. Turn RF POWER CONTROL clockwise for desired output (10-100W). Change to receive by moving T/R switch or releasing PTT.

5-5-9 HOW TO USE THE SPEECH PROCESSOR

Enables greater talk power. Set MIC GAIN CONTROL to 12 o'clock, RF POWER CONTROL fully counterclockwise, COMP SWITCH ON, METER SWITCH COMP. Transmit and turn RF POWER CONTROL clockwise while speaking until desired "PEAK" output power (10-100W) is reached. Adjust MIC GAIN so meter swings 10dB-20dB on COMP scale. For natural voice quality or DX, turn COMP OFF or set MIC GAIN carefully for minimum compression.

5-5-10 HOW TO USE THE VOX CIRCUIT

Built-in VOX allows automatic T/R switching by voice. Set VOX GAIN CONTROL fully counterclockwise (OFF), VOX DELAY fully clockwise, ANTI VOX CONTROL fully counterclockwise. Turn VOX GAIN ON (click). Speak into microphone; T/R switching activates at a certain point. Adjust VOX GAIN for normal voice level. VOX DELAY controls transmit-release time. Adjust ANTI VOX control to prevent speaker sound from activating VOX.

5-5-11 MONITOR

Allows monitoring of transmitting IF signals in SSB mode. Push MONITOR switch ON, adjust MONITOR LEVEL CONTROL for comfortable audio. Use headphones to prevent howling.

5-6 CW OPERATION

5-6-1 RECEIVING

Push MODE SELECT switch for CW or CW-N (with optional narrow filter). Other controls set same as SSB reception. Crystal band pass filter is standard; optional CW Narrow filters improve selectivity (250Hz or 500Hz/-6dB). Pass Band Tuning can narrow bandwidth. Use Noise Blanker, AGC, PREAMP/ATT as needed.

5-6-2 TRANSMITTING

Insert keyer plug into KEY Jack. Set RF POWER CONTROL fully counterclockwise, METER SWITCH Po, VOX GAIN CONTROL OFF. Set T/R switch to TRANSMIT. Key the keyer; meter needle moves. Turn RF POWER CONTROL clockwise for desired output power (10-100W).

5-6-3 CW SIDE-TONE (MONITOR)

When keying, an 800Hz side-tone is heard. Loudness controlled by MONITOR LEVEL CONTROL. Can be used for code practice.

5-6-4 BREAK-IN OPERATION

Uses VOX function for automatic transmit/receive switching. Set T/R switch to RECEIVE, turn VOX GAIN ON. VOX DELAY controls transmit-release time. Full break-in is achieved by setting VOX DELAY fully counterclockwise.

5-7 RTTY OPERATION

Requires a teletypewriter and demodulator (terminal unit) with 2125/2295Hz filters (170Hz shift). Connect to ACC socket pins 8 & 9 via relay or level converter. AF output from ACC socket pin 4 or PHONES jack.

Set mode to RTTY. Tune for 2125Hz (MARK) and 2295Hz (SPACE) audio signals. Use terminal unit tuning indicator. Adjust P.B. Tune for clear reception. Optional CW narrow filter can be used for RTTY NARROW mode.

Diagram Description: Diagrams show RTTY connection for high-speed relay and level converter, including ACC socket pinouts and polarity switch (S1).

5-8 AM OPERATION

5-8-1 RECEIVING

Set mode to AM. Controls similar to SSB, except PBT does not work. Optional crystal filter FL-33 recommended for AM. Tune for maximum signal strength.

5-8-2 TRANSMITTING

Similar to SSB. RF output power adjustable 10-40W via RF POWER control. Speech processor can be used. Meter indicates carrier power.

5-9 FM OPERATION

5-9-1 RECEIVING

Set mode to FM (push FUNCTION KEY then AM switch). Controls similar to SSB, except PBT, Notch Filter, Noise Blanker, AGC, and FILTER SWITCH do not work. Tune for maximum signal strength and clearest audio.

5-9-2 TRANSMITTING

Similar to SSB. Speech processor cannot be used. Meter indicates carrier power. Note: FM mode may be restricted on HF HAM bands except 28MHz.

5-10 GENERAL COVERAGE RECEIVER

In this mode, the set functions only as a receiver, even on HAM bands. Set controls as specified (mostly OFF or counterclockwise). Push POWER switch ON. Frequency, mode, and HAM/GENE mode from VFO A or memory "01" are displayed. Push HAM/GENE switch to display "GENE" for General Coverage mode. For SSB, USB is used on 10MHz+ bands, LSB on 9MHz and below. Push BAND SELECT FUNCTION and TUNING CONTROL to select bands. Tune AF GAIN and TUNING CONTROL for signals.

5-11 OTHER OPERATIONS

5-11-1 VSWR READING

Built-in VSWR meter for antenna matching. Set METER switch to Po, mode to RTTY, and T/R switch to TRANSMIT. Adjust RF POWER control so meter needle points to "SET". Set METER switch to SWR to read VSWR. Antenna impedance should be 50 ohms to avoid damage. Use lowest power setting when in doubt. Use caution.

5-11-2 WWV RECEPTION

To receive WWV, set operating band to 10MHz in HAM or GENERAL COVERAGE mode, tune to 10.000.0MHz, and set mode to any. WWV signal can be used for frequency counter alignment.

5-11-3 SIMPLE FREQUENCY ALIGNMENT

Use WWV signal for alignment. Set frequency to 10.000.0MHz in GENERAL COVERAGE mode, AM. Turn ON MARKER switch. Adjust MARKER CALIBRATOR for zero beat. This calibrates the reference oscillator.

5-11-4 RECEIVE ANTENNA TERMINALS

RECEIVE ANT IN jack connects to receiver input. RECEIVE ANT OUT jack connects to antenna connector via T/R switch. Can be used for a receiving preamplifier, separate receiver, or separate antennas.

5-11-5 TRANSVERTER CONNECTION

Apply +8V to Pin 11 of ACCESSORY socket for transverter control. Transverter terminal is for VHF/UHF transverter input/output. Frequency range 28~30MHz. Input/Output level specifications provided.

5-11-6 LINEAR AMPLIFIER CONNECTION

Rear panel jacks "ALC" and "RELAY" are for keying a linear amplifier and ALC input. Relay capacity is 24V 1A. Optional IC-2KL and IC-AT100/AT500 can be connected. The IC-751 outputs band control voltage from Accessory socket Pin 13.

Diagram Description: A diagram shows internal connections for a linear amplifier (SEND, ALC).

SECTION 6 OPTION INSTALLATION

Tools needed: Phillips screwdriver, screwdriver, solder, de-soldering braid, diagonal cutters, soldering iron (40W), soldering tool.

Preparation: Detach power cord. Remove top/bottom covers and side screws carefully.

6-1 OPTIONAL FILTER INSTALLATION

The IC-751 has two positions for optional filters: "B" for 9MHz filters (FL-32, FL-33, FL-63, FL-70) and "D" for 455KHz filters (FL-52A, FL-53A).

Optional Filters:

• FL-32: 9.0106MHz, CW/RTTY, ±250Hz/-6dB
• FL-63: 9.0106MHz, CW/RTTY, ±125Hz/-6dB
• FL-33: 9.0100MHz, AM, ±3.0KHz/-6dB
• FL-70: 9.0115MHz, SSB (Wide), ±1.4KHz/-6dB
• FL-52A: 455.0KHz, CW/RTTY, ±250Hz/-6dB
• FL-53A: 455.0KHz, CW/RTTY, ±125Hz/-6dB

Filter Switch and PBT Control Functions:

• With FL-70 SSB wide filter: FILTER SWITCH ON/OFF controls NARROW/WIDE bandwidth. PBT CONTROL is EFFECTIVE.
• With CW narrow filter: FILTER SWITCH ON/OFF controls NARROW/WIDE bandwidth. PBT CONTROL is EFFECTIVE.
• With FL-33 AM filter: FILTER SWITCH ON/OFF controls NARROW/WIDE bandwidth. PBT CONTROL is NO WORK. (Cut lead W116 on main board when installing FL-33).

Assembly Procedure: Plug filters into specified positions. For 9MHz filters, remove main unit board screws, tilt board, insert filter, bend leads, and solder.

6-2 BUILT-IN POWER SUPPLY UNIT IC-PS35

6-2-1 SPECIFICATIONS

• Semiconductors: Transistor: 5, IC: 2, Diode: 4
• Input Voltage: 110/220V AC (50/60Hz) ±10%
• Input Capacity: 550VA (at 20A load)
• Output Voltage: 13.8V DC Negative ground
• Max. Load Current: 20A (10 mins ON/10 mins OFF)
• Dimensions: 194(W) x 50(H) x 186(D) mm
• Weight: Approx. 2.3kg
• Kit Included: Main Unit, Insulation Spacer, Power Socket Unit, AC Power Cord, Spare Fuses (2), Installation Screws (6), Insulation Washers (6).

6-2-2 PREPARATION

Detach power cord. Remove top/bottom covers and side screws.

6-2-3 ASSEMBLY PROCEDURE

1. Turn transceiver upside down. Remove "PLATE (A)" from rear panel.
2. Attach main unit (power supply) to bottom cover with screws and insulation washers. Insert insulation spacer.
3. Pass DC power cable through AC power socket plate hole and insert bushing. Attach AC power socket plate using screws from step 1.
4. Pass connector P2' from power socket unit through rear chassis hole and connect to connector P2 from main unit.
5. Connect internal speaker connector, replace covers. Plug P1 into transceiver DC Power Socket.

6-2-4 OPERATION

1. Connect DC output plug P1 to transceiver DC power socket. Ensure transceiver power switch is OFF, T/R switch is RECEIVE, PTT is not depressed, and VOX is OFF.
2. Connect AC power cord to newly installed socket on transceiver rear panel, then to AC outlet.
3. Turn transceiver power switch ON. The unit will supply 13.8V DC.

6-2-5 CAUTION

1. Ground the GROUND TERMINAL with a short wire to prevent shock, TVI, BCI.
2. Unit stops output with protection circuit if shorted or load current exceeds 25A. Turn transceiver OFF and remove cause.
3. If fuse blows, replace with 10A (117V) or 5A (240V) fuse after checking cause. Use a Philips (+) screwdriver.

SECTION 7 BLOCK DIAGRAM

The document includes detailed block diagrams illustrating the internal architecture of the IC-751, including the Main Unit, Logic Unit, Display Unit, PLL Unit, Fil Unit, RF Unit, and PA Unit. These diagrams show the interconnections between various sub-circuits and signal paths for receive and transmit operations across different modes (FM, SSB, CW, RTTY, AM).

SECTION 8 SCHEMATIC DIAGRAM

This section is noted as "SEPARATE" in the Table of Contents, indicating that detailed schematic diagrams are provided as a separate document or appendix.