background image

Summary of Contents for IC-751A

Page 1: ...INSTRUCTION MANUAL x iRgqgi ...

Page 2: ... ICOM philoso phy of providing a product Amateurs want This is it The IC 751A is an all mode HF transceiver and general coverage receiver developed using the most current computer based design techniques and HF engineering Please study this instruction manual thoroughly to learn all functions of the IC 751A and refer back to the manual periodically as necessary Feel free to contact any authorized ...

Page 3: ...ORY SOCKET CONNECTIONS 21 SECTION 6 GENERAL OPERATION 22 6 1 SETTINGS 22 6 2 BASIC OPERATION 22 6 3 SSB OPERATION 25 6 4 CW OPERATION 26 6 5 AM OPERATION 27 6 6 FM OPERATION 28 6 7 RTTY OPERATION 29 6 8 GENERAL COVERAGE RECEIVER 30 SECTION 7 FUNCTIONS OPERATION 32 7 1 VOX OPERATION 32 7 2 SPEECH COMPRESSOR OPERATION 32 7 3 NOISE BLANKER NB OPERATION 33 7 4 CW SEMI FULL BREAK IN OPERATION 33 7 5 SP...

Page 4: ...LLATION 44 10 1 FILTERS 44 10 2 IC PS35 INTERNAL POWER SUPPLY 46 10 3 IC EX310 VOICE SYNTHESIZER UNIT 47 10 4 CR 64 HIGH STABILITY CRYSTAL UNIT 47 10 5 UT 30 PROGRAMMABLE ENCODER UNIT 48 11 CIRCUIT DESCRIPTION 49 11 1 RECEIVE CIRCUITS 49 11 2 TRANSMIT CIRCUITS 50 11 3 PLL CIRCUITS 51 11 4 LOGIC CIRCUITS 52 12 MAINTENANCE AND ADJUSTMENTS 53 12 1 CLEANING 53 12 2 MAINTENANCE 53 12 3 ADJUSTMENTS 53 1...

Page 5: ...r are installed as INCLUDED standard equipment The preamplifier increases receiver sensitivity while the attenuator provides added protection from intermodula tlon problems NEWLY DEVELOPED CPU VARIOUS SCANNING FUNCTIONS Memory Scan allows monitoring of all memory channels or only those storing a particular mode Programmed Scan provides scan ning between any two programmed frequencies Mode Scan aut...

Page 6: ...digit 100Hz illuminated FIP Less than 200Hz from 1 to 60 minutes after power ON Less than 30Hz after 1 hour at 25 C Less than 350Hz in the range of 0 C 50 C 13 8V DC 15 negative ground current drain 20A maximum at 200W input AC power supply is available for AC operation Transmitting At 200 watts input Approx 20 0A Receiving At maximum audio output Approx 1 8A Squelched Approx 1 5A 50 ohms unbalanc...

Page 7: ... 0100MHz SSB CW RTTY 0 1 0 5MHz Less than 0 5 iV for lOdB S N 0 5 1 6MHz Less than 1 iV for lOdB S N 1 6 30 0MHz Less than 0 15 iV for lOdB S N AM NARROW FILTER selected 0 1 0 5MHz Less than 3jLtV for lOdB S N 0 5 1 6MHz Less than 6jLtV for lOdB S N 1 6 30 0MHz Less than IjuV for lOdB S N FM 28 SOM Hz Less than 0 3mV for 1 2d B SI NAD 1 6 SOM Hz Less than 0 3 iV SSB CW RTTY WIDE FILTER selected AM...

Page 8: ...SECTION CONTROL FUNCTIONS ...

Page 9: ...the compression level when the speech compressor Is in use ALC Indicates the ALC level The ALC circuit begins to function when the RF output power reaches a preset level Po Indicates the approximate output power SWR Indicates the SWR of the antenna system after the meter is referenced at SET while the Po meter function is selected This switch is for manually changing between transmit and receive S...

Page 10: ...ing received This control varies the receive audio tone Adjust the control to provide the clearest most pleasing audio Adjust this control for a suitable modulation level while speaking into the microphone in a normal voice Rotate the control clock wise to increase the gain This control varies the RF output power from 10 watts to maximum SSB 100W PEP CW RTTY FM 100W AM BOW Rotate the control clock...

Page 11: ...on ail frequencies from 0 1 to 30MHz The IC 751A does not transmit while in the General Coverage mode This switch activates the optional IC EX310 speech synthesizer which announces the displayed frequency in English MODE SCAN SWITCH MODE S HAM GENE SPEECH MODE S SCAN o a a This switch engages the selective mode function Only memory channels with the same operating mode as is displayed just prior t...

Page 12: ...rotate the TUNING CONTROL to change the displayed frequency Illuminates when the DFS SWITCH function is activated Push this switch and rotate the TUNING CONTROL In order to change your band of operation In the HAM BAND mode the IC 751 A jumps to a factory set initialization frequency on each of the amateur bands as the TUNING CONTROL is rotated In the GENERAL COVERAGE mode the operating frequency ...

Page 13: ...rmation This switch clears the memory which contains the frequency shift information as set with the INCREMENTAL TUNING CONTROL and resets the small incremental tuning display to 0 0 Push the FUNCTION SWITCH first then this switch in order to add the shifted frequency as shown on the incremental tuning display to the frequency on the main frequency display The incremental tuning display resets to ...

Page 14: ...sfer to the selected VFO In the MEMORY CHANNEL mode the displayed frequency and mode transfer to the VFO used immediately prior to changing to the MEMORY CHANNEL mode NOTE When in the MEMORY CHANNEL mode it is the displayed frequency which transfers to the VFO This is not necessarily the MEMORY CHANNEL frequency since the TUNING CONTROL and DFS SWITCH may have been used to shift the operating freq...

Page 15: ...nison with the operator s speech or the closing and opening of the CW telegraph key Full break in operation usable only with CW is the same except the transceiver switches even more rapidly after each element of an individual letter is sent Full break in operation closely simulates full duplex communication VOX GAIN CONTROL GAIN vox DELAY Increases keying speed KEY SPEED This control increases and...

Page 16: ...ATOR SHIFT FREQUENCY INDICATOR SPT lights when separate VFOs are used for the transmit and receive frequencies This allows operation with a transmit frequency which is different from the receive frequency When SPT is not illuminated a single VFO is used for both transmit and receive SCAN lights whenever a scan function is selected VFO A or VFO B lights to indicate which VFO is currently selected M...

Page 17: ...function sound from the speaker may cause unwanted switching of the T R relay Adjust this control in con junction with the VOX GAIN CONTROL so the T R relay switches only from the operator s voice and not from the speaker audio 3 4 REAR PANEL ANTENNA CONNECTOR Connect a 50 ohm impedance antenna to this connector The con nector mates with a PL 259 plug T R CONTROL JACK RELAY EXTERNAL ALC JACK ALC R...

Page 18: ...e from external electronic keyers must be less than 0 4 volts DC When using the IC 751A internal iambic keyer connect an iambic keyer paddle using the supplied 1 4 inch 3 conductor plug See SECTION 4 5 and 6 4 for more information Connect an external speaker to this jack if required Use a speaker with an impedance of 4 16 ohms and remember the built in speaker does not function when using the EXTE...

Page 19: ...tronic instruments or magnetic compasses The optonal IC MB18 mounting bracket allows installation of the transceiver ta a surface over the IC 751 A When mounting the transceiver aboard a boat place the bracket in a location which minimizes vibration and wave shock Antennas play a very important role in radio communication If the antenna is inferior your transceiver cannot give you the best perform...

Page 20: ...NECTOR connections 4 5 CW KEY For CW operation connect a CW key to the KEY JACK using the supplied standard 1 4 inch 3 conductor plug See the diagrams for connection details Note that the keyed voltage when switching with semiconductors or relays with resistors in the circuit must be less that 0 4 volts 4 6 POWER SUPPLY When an AC power supply is required the IC PS35 internal power supply or the I...

Page 21: ...IC PS15 or IC PS30 with the IC 751A CAUTION For safety purposes remember to install FUSES in the DC cable when connecting the IC 751A to a vehicle battery Locate the fuses as close to the car battery as practical 4 7 GROUND To prevent electrical shocks TVI BCI and other problems be sure to ground the equipment with the heaviest gauge wire or strap available from a good ground to the GROUND TERMINA...

Page 22: ...Tuner be used when operating with the IC 2KL and 500 watts output See SECTION 15 The amplifier connections are shown below NOTE All cables required for the interconnec tion of the IC 751A and the IC 2KLare supplied with the amplifier USING NON ICOM EXTERNAL The RELAY JACK on the rear panel of the IC 751A supplies an AMPLIFIERS output from a built in keying relay for an external amplifier The ALC j...

Page 23: ... HF bands therefore It Is suitable for use on the Amateur bands as well as with the IC 751 A general coverage receiver USING THE IC ATIOO or IC AT500 The maximum allowable input for the IC ATIOO is 100 watts there fore the IC AT500 must be used with the 1C 2KL Linear Amplifier SUPPLIED WITH IC AT100 500 ACCESSORY CABLE USING THE AH 2 The AH 2 provides reliable matching for frequencies from 1 8MHz ...

Page 24: ...K operation can also be con nected easily NOTE Some RTTY Terminal Units may require the use of a 20dB audio preamplifier between pin 5 on the ACC SOCKET and the AFSK signal output from the Terminal Unit to provide enough drive for full RF output power from the transceiver The pin 5 input must be approxi mately 150mV rms Check your RTTY Terminal Unit Instruction Manual The AFSK signal may be connec...

Page 25: ... stage Fixed out put regardless of AF output or AF gain 5 Output from the transmit MIC amplifier stage Input for the MIC gain control stage 6 8 volts DC output while transmitting Maximum output current is 5mA 7 Input for external ALC voltage 8 Ground 9 Input for RTTY keying MARK HIGH level SPACE LOW level The levels for MARK and SPACE may be reversed with an internal switch 10 NC no connection 11 ...

Page 26: ...ON POWER OFF OUT AF GAIN MAXIMUM COUNTERCLOCKWISE RF GAIN MAXIMUM CLOCKWISE SQUELCH MAXIMUM COUNTERCLOCKWISE TONE CENTER MIC GAIN CENTER RF POWER MAXIMUM CLOCKWISE DIAL LOCK OFF OUT PBT CENTER NOTCH CONTROL CENTER SWITCH OFF FILTER OFF OUT TS OFF INDICATOR OFF DFS OFF INDICATOR OFF BAND OFF INDICATOR OFF VOX OFF OUT COMP OFF OUT NB WIDE OFF OUT VOX GAIN OFF VOX DELAY FULL NB LEVEL OFF AGC SLOW MET...

Page 27: ...our transmission will not interfere with other communications First set the switches and controls as stated in SECTIONS 6 1 SETTINGS and RECEIVING above 1 Push the PTT SWITCH on the microphone or switch the TRANSMIT RECEIVE SWITCH to TRANSMIT The red TRANSMIT LED lights 2 Speak into the microphone and note that the meter needle follows the modulation of your voice You are now transmitting SSB sign...

Page 28: ...o select the AM mode Refer to SECTION 6 5 for AM operation 2 FM Push FUNCTION and AM SWITCHES ijiumbui AM lani cw Q3 ssB 3SiRTTY Qi i D la 3 CW a 4 SSB USB LSBl mwMJMa AM laa cwBQS ssbES1rtty Q3 a 5 RTTY Push RTTY SWITCH AM CW DSI SSB ESB RTTY BQ3 0 a a Push the FUNCTION SWITCH then the FM SWITCH to select the FM mode Pushing the AM FM SWITCH again returns the trans ceiver to the AM mode Refer to ...

Page 29: ...ncy 14 230 0MHz and USB using VFO A Push the VFO A B SWITCH and the display shows the frequency and mode that is stored in VFO B The frequency 14 230 0MHz and USB are still stored in VFO A however 2 Push the VFO A B SWITCH again and the display shows the VFO A information Each time the switch is pushed the alternate VFO is selected Switching from one VFO to the other VFO does not clear the VFO mem...

Page 30: ...s is useful to check the audio quality of your output particularly important when using the speech compressor DSet the MONITOR MARKER SWITCH on the top panel to MONITOR 6 4 CW OPERATION 1 CW RECEIVING liiwmbiM AM BM rw nna rrr laa rttyisebi A o a 2 Adjust the MONITOR LEVEL CONTROL on the top panel to a comfortable audio level It is preferable to use headphones to prevent howling caused by feedback...

Page 31: ... CW NARROW mode is selected follow the instructions in the CW RECEIVING section 1 Insert the CW key plug into the KEY JACK on the rear panel of the IC 751A 2 Set the switches and controls as shown in the chart SWITCH CONTROL POSITION RF POWER MAX CLOCKWISE METER Po VOX GAIN OFF MAX COUNTERCLOCKWISE 3 Select the transmit mode with the T R SWITCH 4 Operate the CW key The meter movement indicates tha...

Page 32: ...ired power output 3 Set the METER SWITCH to the Po position 4 Adjust the MIC GAIN CONTROL for a slight indication of the meter needle while speaking into the microphone in a normal voice NOTE MIC GAIN CONTROL settings which are too high result in overmodulation and a distorted signal Set the MIC GAIN carefully 5 The speech compressor COMP SWITCH should be turned OFF to prevent overmodulation or di...

Page 33: ...uency is required Refer to SECTION 6 2 VFO A B SELECTION for information on using the two VFOs 2 The encoder tone is transmitted when the FUNCTION SWITCH is pushed while transmitting In addition the FUNCTION INDICATOR lights 6 7 RTTY OPERATION 1 RTTY UNIT CONNECTIONS 2 RTTY RECEIVING JIH14JMM AM nffil cw SSB E13 RTTY EQ3 Q NOTE The FUNCTION INDICATOR lights when the FUNC TION SWITCH Is pushed whil...

Page 34: ... The relay contacts make during the SPACE and break during the MARK 3 Fine adjustment of the MARK and SPACE frequencies can be made by adjusting the trimmer capacitors in the MAIN unit Refer to SECTION 13 4 ADJUSTMENT LOCATIONS USING A LEVEL CONVERTER 1 When a level converter for TTL levels is used connect th6 output of the converter to pin 8 ground and pin 9 on the ACC SOCKET 2 Apply HIGH level 5...

Page 35: ...Push the desired MODE SWITCH When the SSB mode is chosen USB is automatically selected on the 10MHz band and above and LSB is selected on the 9MHz band and below Note however once either USB or LSB mode is automatically selected this mode is maintained regardless of frequency or band changes To change to the opposite sideband push the FUNC TION SWITCH then the SSB SWITCH again 5 Select desired ban...

Page 36: ...he ANTI VOX CONTROL on the top pane clockwise while receiving a signal until the audio from the speaker no longer activates the VOX circuit Refer to SECTION 3 3 for the con trol location 7 2 SPEECH COMPRESSOR OPERATION The IC 751 A has a low distortion RF speech compressor circuit which provides greater talk power by improving the intelligibility of the transmitted signal over long distances 1 Set...

Page 37: ...rmed automatically by the transceiver whenever the keying starts or stops The receive to transmit switching time is almost instantaneous whereas the transmit to receive switching time may be varied by an adjustment SEMI BREAK IN OPERATION USING A STRAIGHT KEY 1 Set the controls and switches as shown in the table SWITCH CONTROL POSITION MODE CW or CW NARROW VOX ON IN KEY SPEED OFF VOX DELAY 10 O CL...

Page 38: ...SE TRANSMIT RECEIVE RECEIVE 2 Adjust the KEY SPEED CONTROL for a suitable keying speed 3 The transmit receive switching is automatically performed by the transceiver The purpose of the split function is to allow an operator the option of transmitting on a frequency different from the receive frequency Push the SPLIT SWITCH to turn the function ON or OFF 1 Store the frequency 7 057MHz in VFO A and ...

Page 39: ...h the receive crystal filter 1 The PBT CONTROL has a detent at the center 12 o clock position This position provides the widest bandwidth and the control should normally be left here 2 The PBT CONTROL may also be used to adjust the tone of the receive audio for maximum intelligibility 3 While receiving in the LSB mode narrow the bandwidth by turning the PBT CONTROL counterclockwise to eliminate in...

Page 40: ...Hz 1 ON NARROW or RTTY NARROW mode requires either an optonal FL 52A or FL 53A narrow filter 2 3 Internal preset switch S4 on the MAIN unit reverses these narrow and wide filters FILTER SWITCH OUT 2 3kHz FILTER SWITCH IN 500Hz 4 5 Internal preset switch S3 on the MAIN unit reverses these wide and narrow filters FILTER SWITCH OUT 3kHz FILTER SWITCH IN 8kHz By using the RIT circuit it is possible to...

Page 41: ...ft value resets to 0 0 and the receive and transmit frequencies become the same whether the RIT function is ON or OFF 6 Push FUNCTION SWITCH then push RIT lTX CLEAR SWITCH USB RIT V 6 1 8 3 5 0 1 m A TX OPERATION 6 To add the RIT shift value to the displayed frequency push the FUNCTION SWITCH then push the HWAJX CLEAR SWITCH The RIT shift value automatically resets to 0 0 m cw 1393 a The ATX circu...

Page 42: ...2639MHz Transmit 14 2639MHz Receive 14 2678MHz Transmit 14 2639MHz USB RIT sn USB TI V B 1 B DO n 1 LI 1 I8PB IB DO n 1 D D LI 1 VFO A m A 5 Push TX SWITCH to turn OFF the TX func tion 5 Push the ATX SWITCH again to turn OFF the ATX function The letters TX and the amount of shift are no longer displayed 6 When the ATX function is OFF the transmit and receive fre quencies are as indicated on the fr...

Page 43: ...itat ing background noise from being heard during the short pauses in speech The damping effect of the AGC therefore allows accurate S meter readings to be taken of the peak IF signal strength 1 For normal SSB reception select the SLOW position 2 For CW or AM signals or for SSB signals with short interval fading select the FAST position In the FAST position the time constant of the circuit is shor...

Page 44: ... the transceiver in the MEMORY CHANNEL mode The frequency operating mode and HAM GENE mode which have been stored in memory channel 01 are displayed The letters MEMO above the memory channel number indicate that the MEMORY CHANNEL mode is currently selected 3 Rotate the TUNING CONTROL to select any of the memory channels When memory channels not yet programmed are selected only the MHz and kHz dec...

Page 45: ...s used to automatically scan all programmed memory channels 1 Program memory channels 1 Program the desired frequencies into memory channels NOTE Random frequencies were stored in the memory chan nels at the factory for testing purposes 2 Adjust SQUELCH CONTROL 2 Adjust the SQUELCH CONTROL to quiet the noise output from the speaker 3 Push SCAN SWITCH 3 Push the SCAN SWITCH and the IC 751A begins s...

Page 46: ... 01 and MEMO 02 using either the HAM or the GENE mode HAM mode limits must be in the same band 3 Adjust SQUELCH CONTROL 3 Adjust the SQUELCH CONTROL to quiet the noise output from the speaker NOTE If the RECEIVE INDICATOR remains ON for example if the SQUELCH CONTROL is rotated fully counter clockwise the scan will not stop at any signals 4 Push SCAN SWITCH 4 Push the SCAN SWITCH to start the scan...

Page 47: ...SWR Read the VSWR from the SWR scale NOTE Always use a 50 ohm antenna system in order to obtain full output power and to avoid possible damage to the transmitter The signal from radio station WWV or WWVH may be used for alignment of a frequency counter the marker oscillator or the fre quency display 1 Select the 10MHz band using either the HAM BAND or GENERAL COVERAGE mode 2 Push the AM SWITCH 3 U...

Page 48: ...S MODE FILTER SWITCH 9MHz FILTER 455kHz FILTER STANDARD BANDWIDTH P B T USB LSB OUT FL 80 FL 44A 2 3kHz YES IN FL 80 CFJ455K5 2 6kHz YES CW RTTY OUT FL 32A FL 44A 500Hz YES IN FL 80 FL 44A 2 3kHz YES CW RTTY NARROW OUT FL 32A FL 52A FL 53A 500Hz 250Hz YES IN FL 80 FL 52A FL 53A 500Hz 250Hz IF SHIFT AM OUT THROUGH CFW455HT 8kHz NO IN THROUGH CFJ455K5 3kHz NO FM OUT THROUGH CFW455E 15kHz NO IN THROU...

Page 49: ... right edge of the MAIN unit upwards taking care not to damage the sockets and plugs that are installed on the unit 3 The filter must be installed at position A in the photo there fore remove the FL 32A original filter from the MAIN unit using de soldering braid 4 Install the FL 63A at position A Orient the label on the filter in the same manner as the other filters already installed 5 Bend the le...

Page 50: ...wn Remove PLATE A attached to the rear panel by unscrewing the four screws These screws will be used later 2 Attach the IC PS35 to the bottom cover with the supplied screws and insulating washers Also insert the insulating gasket between the IC PS35 and the bottom cover 3 Pass the DC power cable attached to PI through the hole of the AC power socket plate as shown in the illustration then insert t...

Page 51: ...the transceiver to have the displayed frequency announced in English 3 The volume of the announcement is adjustable with R16 on the voice synthesizer Adjust R16 for a comfortable audio level 4 The W1 jumper wire controls the speech speed Cut W1 to increase the speech speed 5 Replace the top and bottom covers of the transceiver when adjustments are completed 10 4 CR 64 HIGH STABILITY CRYSTAL UNIT I...

Page 52: ...rogram the unit for the frequency required using the program ming chart The UT 30 is factory programmed for 88 5Hz 5 Replace the transceiver cover Refer to SECTION 7 6 FM REPEATER OPERATION for Instruc tions regarding operation NOTE Install and solder a jumper wire in each position indi cated by 1 in the table below SUBAUDIBLE TONE ENCODER PROGRAMMING CHART Above unit is programmed for an 88 5Hz t...

Page 53: ... 4515MHz R18 L13 and Cl 4 are for feedback to improve the frequency characteristics of Q2 The first IF signal is filtered by the FI1 monolithic crystal filter 7 5kHz 3dB and is then amplified by the 08 dual gate FET The second gate of 08 is controlled by the AGC voltage The signal is fed through the D19 T R switching diode and a high pass filter to the second IF mixer of the IC3 double balanced mi...

Page 54: ...front panel The AF power amplifier has a 2 6W output capability under an 8 ohm load with 10 distortion 11 2 TRANSMIT CIRCUITS 1 AF CIRCUITS MAIN UNIT RF COMPRESSOR RF UNIT The AF signal from the mic connector is fed through the MIC GAIN CONTROL on the front panel to Q34 and Q35 where the signal is amplified The tone control circuit is installed between 034 and Q35 and varies the frequency response...

Page 55: ...rent of Q2 and Q3 is controlled by the junction voltage of D1 The current is set at about 100mA by R27 R30 prevents the set value from deviating due to variations of D1 characteristics The output of Q2 and Q3 is fed to the L4 impedance matching section and is amplified by the Q4 and Q5 class AB push pull am plifier to provide 100 watts output power 11 3 PLL CIRCUITS The PLL unit outputs two oscill...

Page 56: ...his unit includes an 8 bit NMOS CPU a 4 bit Ik word CMOS RAM a multi purpose custom 1C and I O expander IC s CIRCUIT A multi function CMOS 1C is used This custom 1C is contained in a 40 pin OIL package a An external L and C are connected to pins 18 and 19 to give an approximate clock signal of 100kHz b ATS from pin 32 is HIGH if the TUNING CONTROL Is rotated faster than a set speed The set speed i...

Page 57: ... adjustment The IC 751 A uses an advanced highly reliable RAM integrated circuit which is completely separate from the transceiver s main microprocessor The purpose of the battery is to provide power to the RAM so it retains all memory information during power failures or when the unit is unplugged or turned off The usual life of the lithium battery exceeds ten years It is advisable to monitor the...

Page 58: ...tinuously from 5 to 45 words per minute The R8 WEIGHT CONTROL is set fully counterclockwise at the factory which sets the DOT SPACE DASH ratio at 1 1 3 DOTS and DASHES increase in length if R8 is turned clockwise 4 CW SIDETONE FREQUENCY ADJUSTMENT 1 This control is factory set for a 700Hz tone 2 Connect a CW key to the KEY JACK on the rear panel and select the CW mode 5 SCAN SPEED ADJUSTMENT 6 BFO...

Page 59: ......

Page 60: ...Mixer 56 ...

Page 61: ......

Page 62: ...SECTION 14 BLOCK DIAGRAM ...

Page 63: ......

Page 64: ...ICOM INCORPORATED 1 6 19 KAMIKURATSUKURi HIRANO KU OSAKA 547 JAPAN A 0762 Printed in Japan ...

Reviews: