Connection
Connect the controller’s USB Type-C to the PC with a data-capable cable. USB carries CI-V and TX/RX audio; no separate audio interface is needed. Use the official IC-905 driver. Two virtual COM ports appear: A/B. Select IC-905 Serial Port A (CI-V) for CAT.
Radio settings · AFSK
Open MENU → SET → Connectors. TX audio: MOD Input; RX audio: USB/AV-OUT AF/IF Output. USB input here means audio via the connector, not USB sideband.
| Item | Setting / check |
|---|---|
| Mode | Start with LSB-D: SSB Data, not the radio’s native RTTY mode. |
| MOD Input → DATA MOD | USB: shared by LSB-D/USB-D. Factory default is USB, but check for changes from presets or earlier use. |
| MOD Input → USB MOD Level | Keep the working FT8 value first. Factory default: 50%. Adjust with PSRTTY TX volume. |
| USB/AV-OUT AF/IF Output → Output Select | AF: sends received audio to the PC. |
| USB/AV-OUT AF/IF Output → AF SQL | OFF (OPEN): prevents radio squelch from cutting PC audio. |
| USB/AV-OUT AF/IF Output → AF Output Level | Keep the working FT8 value and check PSRTTY RX level. |
| CI-V → CI-V Address | Factory default: ACh. Match PSRTTY to the actual radio CI-V address. Keep an intentionally changed address and match the current setup. |
| USB (B) Function | Use Port A for CAT. Port B serves RTTY Decode, DV Data or Weather; unlike MK2, it has no CI-V selection. PSRTTY audio decoding does not need Port B RTTY Decode. |
| USB SEND/Keying → USB SEND / USB Keying (RTTY) | CAT PTT in this guide does not use DTR/RTS SEND or FSK keying. Set OFF unless needed for another dedicated use. |
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) | USB (A) DTR / USB (B) DTR |
| USB Keying (CW) | OFF |
| USB SEND | OFF |
| Operating mode | RTTY / RTTY-R |
| RTTY shift | 170 Hz |
| RTTY Mark frequency | 2125 Hz |
For radios with A/B ports
| Shared CI-V port | USB Keying (RTTY) |
|---|---|
| A | USB (A) DTR |
| B | USB (B) DTR |
A/B identifies a port; DTR/RTS identifies its line. When sharing CI-V, select the same A/B side for USB Keying (RTTY). CI-V on B depends on the model/port-function setting. The original IC-7300 has no A/B choice: select DTR/RTS only.
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.
If FT8 already works
With FT8 in USB-D, LSB-D uses the same DATA MOD and USB MOD Level. Check actual LSB-D after PSRTTY connects and keep input/gain first. Plain USB uses DATA OFF MOD; check DATA MOD separately for LSB-D.
PSRTTY settings · AFSK
Select IC-905 and CI-V CAT PTT. Choose the Serial Port A (CI-V) COM and explicitly select the same IC-905 USB audio device for Audio IN/OUT. Start with LSB-D. Match the actual CI-V address. Close other apps using the same COM.
No modulation
Compare FT8/PSRTTY outputs → check actual LSB-D → DATA MOD = USB → USB MOD Level and PC/PSRTTY TX volume. For CAT failures, first check Port A COM and CI-V address. For RX, check AF, AF SQL and AF Output Level under USB/AV-OUT AF/IF Output, plus PSRTTY Audio IN.
Official sources
- IC-905 — Icom
- IC-905 取扱説明書
- IC-905 BASIC MANUAL (English), 3-2 / 8-14–8-15 / 13-3
- USB driver installation guide — Icom
Based on official IC-905 documentation. Menu names/positions may vary with firmware or language.