Icom IC-751 [28/37] 8 am operation
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Icom IC-751 [28/37] 8 am operation

Icom IC-751 [28/37] 8 am operation

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5 8 AM OPERATION If you wish to receive RTTY signals which have wider shift such as 425Hz and 850Hz shifts prepare a demodulator suits for the shift and use normal RTTY mode 5 8 1 RECEIVING Set the operating mode for AM by pushing the MODE SELECT switch AM The other controls are the same as those for SSB reception except the Pass Band Tuning The Pass Band Tuning control does not work in this mode The optional crystal filter FL 33 will provide good selecti vity for AM reception Refer to the installation instruc tions 6 1 OPTION INSTALLATION on page 28 5 7 2 TRANSMITTING For keying of the Frequency Shift Keying FSK circuit insert a high speed relay s coil into the loop current circuit of the teletypewriter and connect the relay contacts to Pins 8 and 9 of the ACC Socket on the rear panel The relay contacts make during the Space and break during the Mark as shown in the drawing Fine adjustment of the MARK and SPACE frequencies can be done by adjusting the coil cores in the MAIN unit When tuning an AM signal tune for maximum signal strength as indicated on the meter When a level converter for TTL level signals is used connect the output of the converter to Pins 8 ground and 9 of the ACC Socket apply High level 5V signals for the Mark and Low OV for the Space 5 8 2 TRANSMITTING Transmitting AM signals is essentially the same as SSB transmission Set knobs and switches the same as for SSB operation The RF output power can be adjusted between 10 Watts and 40 Watts by the RF POWER control Also the speech processor can be used on this mode If your teletype machine puts out signals which are reverse polarity LOW level OV is for MARK and HIGH level 5V is for SPACE slide S1 on the MAIN unit board to arrow direction as shown in the photo below When transmitting the AM signals the meter in Po posi tion will indicate the carrier power and the meter needle will move slightly according to your voice S1 RTTY Polarity Switch NORMAL REVERSE MARK H MARK L 5 9 FM OPERATION S2 RTTY Shift Switch 170Hz 850Hz 5 9 1 RECEIVING Set the operating mode for FM by pushing the FUNCTION KEY first then the MODE SELECT switch AM The other controls are the same as those for SSB reception however the Pass Band Tuning control Notch Filter Noise Blanker AGC circuits and FILTER SWITCH do not work in this mode L3 MARK Frequency Adjust L4 SPACE 170Hz Shift Freq AdjJ J L5 SPACE 850Hz Shift Freq When tuning an FM signal tune for maximum signal strength as indicated on the meter and the clearest audio When using an AFSK generator that has 2125Hz for Mark and 2295MHz for Space connect the output signals for the AFSK to the Mic connector on the front panel and set the Mode to LSB See Other Operations chapter Doing this you can use the VOX operation available in this mode and receive transmit changeover is very easy 5 9 2 TRANSMITTING Transmitting FM signals is essentially the same as SSB transmission Set knobs and switches the same as for SSB operation However the speech processor can not be used on this mode When transmitting the FM signals the meter in Po posi tion will indicate the carrier power but the meter needle does not move according to your voice such as SSB trans mitting NOTE Most countries may not allow to use the FM mode on HF HAM bands except 28MHz 25

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