RTTY Interfacing

The Super Combo Keyer can be used as a transmit interface between a RTTY program using a PC soundcard and a radio.  The 2 radio functionality for SO2R operation is limited with RTTY unless external switching devices are added.

Sending RTTY using AFSK:  

Feed the AFSK output from the soundcard directly into the MIC input of the SCK.  Switch the noise gate and compressor OFF.  Adjust the AFSK level to the radio with the MIC level control on the front panel.  If more attenuation is required the output level can be reduced even further by adjusting the pot next to the radio connector at the back of the keyer.   The PTT can be done either by switching the radio to VOX mode or via the PTT circuit in the serial (COM) port if the RTTY program supports that. 

The RX audio from the radio is fed directly to the Line Input of the PC Soundcard.  

Sending RTTY using FSK:

FSK keying has proved for me to be the most reliable option and being an Icom user it was the only option because of the fact that the  Icom 746 and 781 I own only allows FSK type sending when in RTTY mode.

A RTTY program like MMTTY has all the features to allow easy interfacing to almost any modern Amateur radio via the Super Combo Keyer.  To send RTTY using FSK the radio needs to be in transmit mode and the FSK input pin must be pulsed with the data.

In the MMTTY setup page under "Misc"  select "COM-TxD (FSK)".  In the "TX" page select the COM port on the PC where the COM cable to the radio is plugged in.  Also select "Invert logic" on the same page if the PTT stays on when MMTTY is started. PTT in this case is done via the PTT circuit (Pin 7) in the serial (COM) port.

The only change that must be made to the wiring is the output cable from the CI-V must be removed from the radio and connected to the FSK input pin on the radio.  For this purpose a short adaptor pigtail can be made up to connect the CI-V plug into the FSK input.  The CI-V radio control function will be lost while MMTTY is being used.  MMTTY does not support radio control.  Band changes etc must be done manually by th operator.

The RX audio is fed directly into the PC Soundcard either from the radio speaker or the fixed output level on the ACC socket of the radio.

Note: MMTTY is used as an example because it was tested and it works perfectly.  WriteLog or any other RTTY program that has an FSK output on pin 3 of the COM should work.

Last updated 15 January 2001 by [email protected]

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