Icom CI-V, CAT control and keying safely
CI-V is how an Icom is told what to do — frequency, mode, and on most rigs the transmitter itself. It is a simple protocol with three settings that account for nearly every problem people have with it, and one failure mode worth taking seriously.
The three settings that matter
- Address. Every Icom model has a default CI-V address — an IC-7300 is
94h, others differ. The radio and the software must agree. A mismatch is the usual reason rig control does nothing whatsoever. - Baud rate. Often defaults to 19200, sometimes to Auto. If control is intermittent, pin it to a fixed rate at both ends — Auto has to guess, and it guesses wrong often enough to be worth ruling out.
- Transceive. Leave it off unless you have a reason. It makes the radio announce every change on the bus unprompted, which is helpful when two devices must stay in step and unhelpful when a program is not expecting it.
Why CAT is worth having
With rig control connected, the frequency in your log is the frequency you actually transmitted on, because the software read it from the radio rather than from a box you typed in and forgot to update. On a picture mode where a single transmission runs for minutes, that is the difference between a log worth keeping and one worth checking.
The failure worth taking seriously
Serial commands go missing. Cables get nudged, adapters glitch, buffers overflow. That is unremarkable for a frequency change — you resend it. It is not unremarkable for “stop transmitting”.
If a program sends the release, assumes it worked and moves on, a dropped command leaves the radio keyed while the screen cheerfully reports receiving. The operator has no reason to look. An unattended carrier sits on the air until someone notices the heat, the SWR or the silence from everyone else on frequency.
What Open Signal does
- Waits for confirmation rather than treating a sent command as a completed one.
- Retries the release if that confirmation does not arrive.
- Reads back the radio’s actual state, so what the screen says is what the rig is doing rather than what the software last asked for.
None of that is clever — it is just refusing to assume. But it is the difference between a transmitter that stops when you tell it to and one that usually does.
Or use VOX
Data-mode VOX keys the radio when audio arrives and unkeys when it stops. It needs no serial line, no address and no configuration beyond switching it on — and if the software stops for any reason, the audio stops with it and the radio drops out naturally. It is a perfectly respectable choice.
CI-V questions
What is CI-V?
CI-V is Icom's rig-control protocol — the equivalent of Yaesu's or Kenwood's CAT. It is a simple serial bus where each radio has an address, so several radios and controllers can in principle share one line. On a modern Icom with built-in USB it runs over the same cable as the audio.
What is my radio's CI-V address?
Every Icom model has its own default: an IC-7300 is 94h, and other models differ. It is set in the CI-V section of the radio's menu, and the controlling program needs to be told the same value. If rig control does nothing at all, a mismatched address is the first thing to check.
Should CI-V Transceive be on or off?
Off, unless something on the bus genuinely needs it. Transceive makes the radio broadcast every frequency and mode change unprompted. That is useful when two devices must stay in step, but it puts traffic on the bus that a program may not be expecting, and it is a common cause of erratic rig control.
Why would a radio be left transmitting?
Because a serial command can go missing. If a program sends 'stop transmitting' and simply assumes it worked, a dropped or corrupted command leaves the rig keyed while the screen says receiving. It is the one CAT failure with real consequences — an unattended transmitter on the air.
How does Open Signal avoid that?
It does not assume the command worked. After keying down it waits for the radio to confirm, retries the release if the confirmation does not come, and reads back what the radio is actually doing rather than trusting its own record of what it sent.
Is CAT PTT better than VOX?
Neither is better in general. VOX needs no wiring or configuration and cannot leave a radio keyed if the software crashes, because the audio simply stops. CAT PTT is cleaner, keys exactly when asked and does not care about background noise. Plenty of operators run VOX for years without trouble.
More about Open Signal
CAT sorted? Put a picture on the air
Open Signal drives Kenwood, Elecraft, Yaesu and Icom rigs, follows the VFO for the log, and receives free forever without a licence key.