IC-7400 / IC-746PRO | Radio setup guides

Connection

Connect rear REMOTE (CI-V) to the PC using a compatible CI-V interface. Connect external sound hardware/radio interface to ACC(1) (8-pin). A USB CI-V cable alone carries no audio. TX: PC output → MOD; RX: AF → PC input.

Radio settings · AFSK

This guide uses ACC AFSK audio. On IC-7400/IC-746PRO, select LSB and hold SSB 1 second for LSB-D. Data mutes the microphone and uses ACC(1). For HF use 8-pin ACC(1); do not confuse it with the 6-pin DATA procedure.

Item	Setting / check
Mode	Select LSB on the radio, then hold SSB for about 1 seconds for LSB-D. Data mode mutes the microphone.
ACC(1) (8-pin) pin 4 MOD	Interface TX audio → ACC(1) (8-pin) pin 4 MOD.
ACC(1) (8-pin) pin 5 AF	ACC(1) (8-pin) pin 5 AF → interface RX input. Normally independent of the AF knob.
ACC(1) (8-pin) pin 2 GND	Connect pin 2 GND as specified by the audio interface.
ACC(1) (8-pin) pin 3 SEND	Pin 3 SEND: contact input if the interface uses PTT. Separate PTT wiring is unnecessary for this CAT PTT connection.
CI-V Address	Default 66h. Match PSRTTY to the radio’s actual CI-V address.
CI-V Baud Rate	Match CI-V Baud Rate and PC speed.
Audio TX level	Start with low PC/interface/PSRTTY TX volume. There is no USB MOD Level setting on the radio.

FSK keying transmission · Ver1.18

Example: DTR for FSK and CI-V/CAT for PTT. Adjust settings to your wiring and selected signals.

Serial keying for TX; Audio IN for RX. Neither primary nor secondary Audio OUT is used. Check radio RTTY mode, 170 Hz shift and Mark frequency. Keying polarity is independent of RX inversion.

The manufacturer manual uses the ACC RTTY keying input for FSK. A separate serial port and a suitable FSK interface are required. A USB socket does not mean FSK is available with only a USB cable. Never connect RS-232 signals directly to ACC.

Radio settings

Radio item / connection	Setting / matching
FSK input / keying	ACC (1): RTTY / FSK
Serial connection	Use a separate FSK COM port from CAT for this model. Check the connection and avoid PTT signal conflicts.
Operating mode	RTTY / RTTY-R
RTTY shift	170 Hz
RTTY Mark frequency	2125 Hz
PTT (TX/RX switching)	Do not assign the same line to PTT and FSK
Audio IN	Use the usual receive audio input

The manufacturer manual uses the ACC RTTY keying input for FSK. A separate serial port and a suitable FSK interface are required. A USB socket does not mean FSK is available with only a USB cable. Never connect RS-232 signals directly to ACC. With external control set to radio PTT, a dedicated FSK COM can share different lines, for example FSK=DTR and PTT=RTS. Keep this port separate from CAT and never assign both functions to one line.

Keying polarity mapping

PSRTTY inversion	DTR OFF	DTR ON
Not inverted	Mark	Space
Inverted	Space	Mark

This table maps PSRTTY control signals. It is independent of A/B selection and RX decoding inversion. Start without inversion, then match the radio/interface polarity.

Manufacturer reference: manual / USB port settings (IC-7400 / IC-746PRO)

If FT8 already works

If FT8 works in USB-D through the same external audio device, keep audio wiring/gain first, then select LSB-D on the radio for RTTY. If FT8 used plain USB, also check that Data mode mutes the microphone.

PSRTTY settings · AFSK

Select IC-7400 / IC-746PRO, the CI-V interface COM and explicit external Audio IN/OUT devices. For this guide, turn automatic mode switching on connection OFF and set mode on the radio; older Data-control commands differ from current models. Close apps using the same COM.

No modulation

Compare FT8/PSRTTY output devices → check radio mode → TX audio to MOD and RX audio from AF → interface levels. If CAT works but no modulation, check audio cable and Audio OUT first.

Official sources

Based on official manuals. IC-746 and IC-746PRO use different mode procedures and have separate guides.