Connection
Connect rear USB B (Type-B) to the PC with a data cable. USB carries CI-V and TX/RX audio; no separate audio interface is needed. USB A is for a keyboard and similar devices. Install the official driver and select the CI-V COM (USB1) from USB B.
Radio settings · AFSK
Audio settings: SET [F-7] → ACC [F-2]. Check DATA1 MOD–DATA3 MOD, USB MOD Level, USB Output Select, USB AF SQL and USB AF Output Level. CI-V settings: SET → OTHERS. USB audio input differs from USB sideband.
| Item | Setting / check |
|---|---|
| Mode | Start with LSB-D: SSB Data, not the radio’s native RTTY mode. |
| ACC → DATA1 MOD | PSRTTY 1.16 auto-switches Data to D1: check DATA1 MOD = USB. Factory default is ACC-A. D2/D3 input settings are separate: check the Data number even if FT8 works. |
| ACC → USB MOD Level | Keep the working FT8 value first. Factory default: 50%. Adjust with PSRTTY TX volume. |
| ACC → USB Output Select | AF: sends received audio to the PC. |
| ACC → USB AF SQL | OFF (OPEN): prevents radio squelch from cutting PC audio. |
| ACC → USB AF Output Level | Keep the working FT8 value and check PSRTTY RX level. |
| OTHERS → CI-V Address | Default 8Eh. Match PSRTTY to the radio’s actual CI-V address. |
| OTHERS → CI-V USB Port / CI-V USB Baud Rate | Check CI-V USB Port and baud rate. For Unlink from [REMOTE], match CI-V USB Baud Rate to PSRTTY; when linked, match CI-V Baud Rate. Keep working FT8 settings first. |
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.
Connect the radio to the PC with one USB cable to use FSK. See FSK keying output for the radio settings.
Radio settings
| Radio item / connection | Setting / matching |
|---|---|
| USB Keying (RTTY) | USB1 DTR / USB2 DTR |
| USB Keying (CW) | OFF |
| USB SEND | OFF |
| Operating mode | RTTY / RTTY-R |
| RTTY shift | 170 Hz |
| RTTY Mark frequency | 2125 Hz |
IC-7851 uses USB1/USB2, not A/B. Match USB Keying (RTTY) to USB1 DTR/RTS or USB2 DTR/RTS for the actual FSK COM port. Set USB SEND to OFF for CI-V PTT, or to a separate signal line for line-based PTT.
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-7851)
If FT8 already works
Even with FT8 in USB-D, check DATA1/2/3. USB-D and LSB-D share input only for the same Data number. FT8 DATA2 may already use USB, but PSRTTY 1.16 auto-switches to DATA1, so DATA1 MOD must be USB. Plain USB uses DATA OFF MOD. Keep the working FT8 USB MOD Level first.
PSRTTY settings · AFSK
Select IC-7851 and CI-V CAT PTT. Explicitly select its USB CI-V COM and the same IC-7851 USB audio device for Audio IN/OUT. Start with LSB-D. Close other apps using that COM.
No modulation
Compare FT8 and PSRTTY output devices → verify LSB-D after connection → check DATA1 MOD = USB → check USB MOD Level and PC/PSRTTY transmit volume. Start with low audio and observe radio power and ALC.
Official sources
Based on official IC-7851 documentation. Menu names/positions may vary with firmware or language.