Icom IC-751 [27/37] 7 rtty operation
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Icom IC-751 [27/37] 7 rtty operation

Icom IC-751 [27/37] 7 rtty operation

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In addition to the crystal band pass filter CW Narrow filters are optional for this unit Refer to 6 1 OPTIONAL FILTERS on page 28 Control clockwise will make the transmit release time longer Set it for your own keying speed By turning the VOX DELAY control fully counterclockwise and click OFF to the FULL position the break in function reaches FULL BREAK IN So you can watch on the receiving frequency in the interval of each dot or dash Switch is set at the CW N mode this filter is activated and the total selectivity of CW reception is improved 250Hz or 500Hz 6dB Also with this filter internal noise is reduced for comfortable CW reception and an improved signal to noise S N ratio If the optional CW filter is not installed the set does not work in the CW N mode 5 7 RTTY OPERATION For RTTY operation a teletypewriter or an equivalent and a demodulator terminal unit which is operational with audio input are required Any demodulator with 2125 2295Hz filters narrow 170Hz shift can be used with the IC 751 The Pass Band Tuning system can be used to narrow the bandwidth up to 800Hz the same as in the SSB mode Also use the Noise Blanker AGC switch and or PREAMP ATT switch depending on the receiving conditions the same as SSB reception When a highspeed relay is used 5 6 2 TRANSMITTING Insert the keyer plug into the KEY Jack on the rear panel of the unit and set knobs and switches as follows RF POWER CONTROL METER SWITCH VOX GAIN CONTROL Fully counterclockwise Po OFF Completely Counterclockwise When a level converter is used Other knobs and switches are set the same as for CW reception By setting the T R switch to TRANSMIT the TRANSMIT indicator is lit and shows that you are ready for CW trans mission When you key the keyer the meter needle moves and your CW signal is transmitted To increase the trans mitting power turn the RF POWER Control clockwise to adjust while watching the meter needle on the Po scale for the desired output power 5 7 1 RECEIVING Audio signals for the demodulator can be supplied from Pin 4 of the ACC socket on the rear panel or from the PHONES jack on the front panel The level of the audio signals from Pin 4 of the ACC socket does not vary by turning the AF GAIN Control and the level is about 300mVp p maximum 5 6 3 CW SIDE TONE MONITOR When keying the side tone oscillator is activated and an 800Hz tone will be heard The loudness of the tone is controlled by the MONITOR LEVEL Control located on the top Rotating the control clockwise will increase the loudness This tone is also audible in the receive mode and can be used for code practice adjustment of the keyer etc Set the operating mode for RTTY by pushing the MODE SELECT switch RTTY The other controls are the same as those for SSB reception When tuning a RTTY signal set the TUNING RATE SELECT switch OFF out position and tune to get audio signals of 2125Hz for MARK and 2295Hz for SPACE Use the tuning indicator of the terminal unit for easy tuning Also adjust the P B Tune control for clear reception 5 6 4 BREAK IN OPERATION The IC 751 has Break In CW capability when using the VOX function When keying the unit is automatically set in the transmit mode After keying it is returned to the receive mode also automatically after a given transmit release delay time constant Leave the T R switch in the RECEIVE position and turn the VOX GAIN control clockwise to click ON When an optional CW narrow filter is installed by setting the set in the RTTY NARROW mode By pushing the FUNCTION KEY first then the RTTY switch the narrow filter is activated and the total selectivity of the RTTY reception is improved 250Hz or 500Hz 6dB the same as the CW mode The transmit release delay time constant is set by adjusting the VOX DELAY Control Turning the VOX DELAY 24

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