diff --git a/internal/cat/tci_tx_probe.go b/internal/cat/tci_tx_probe.go
index 3dd6b56..a376991 100644
--- a/internal/cat/tci_tx_probe.go
+++ b/internal/cat/tci_tx_probe.go
@@ -8,11 +8,13 @@ package cat
 //  1. The radio asks for audio only when the transmission is the CLIENT'S. With
 //     the operator keying the microphone it sent 282 receive frames and nothing
 //     else, over six seconds.
-//  2. It asks only in a DIGITAL mode. Keyed from here in SSB: nothing, four
-//     times over. The same button in DIGU: chrono frames immediately. In SSB the
-//     modulator is wired to the microphone and no amount of network audio will
-//     reach it — which is also the honest answer to "why can I hear myself but
-//     not the tone".
+//  2. It asks only when its TRANSMIT AUDIO SOURCE is TCI rather than the
+//     microphone. This first read as "digital modes only" — SSB produced
+//     nothing four times over, DIGU answered at once — but the mode was a
+//     coincidence: ExpertSDR3 keeps that source setting per mode, and it was on
+//     the microphone in SSB. Which is why nothing is refused on the strength of
+//     the mode: the radio is asked, and it answers by asking or by staying
+//     quiet.
 //  3. The chrono is a REQUEST, not a clock to follow. It carries no payload —
 //     the message itself is the ask — and it names the size it wants in the
 //     header's length field: 2048 samples, two channels interleaved, arriving
@@ -118,9 +120,12 @@ func (t *TCI) setTXFeed(fn func(samples int) []byte) {
 // ProbeTXStream keys the radio, answers its chrono requests with a tone for the
 // given number of seconds, unkeys, and reports what happened.
 //
-// INTO A DUMMY LOAD, AND IN A DIGITAL MODE. In SSB the radio takes the
-// microphone and this produces nothing — which is a property of the radio, not
-// a fault here, so it is said rather than worked around.
+// INTO A DUMMY LOAD. Confirmed on a SunSDR: 80 W out of a 1 kHz tone at 70% of
+// full scale into 80% drive.
+//
+// If the radio's transmit audio source is the microphone rather than TCI it
+// will not ask for anything, and this stops within a fifth of a second and says
+// which setting to change.
 func (t *TCI) ProbeTXStream(seconds int, toneHz float64) error {
 	if seconds <= 0 {
 		seconds = 5
@@ -144,10 +149,15 @@ func (t *TCI) ProbeTXStream(seconds int, toneHz float64) error {
 		return fmt.Errorf("the radio refuses transmitting (tx_enable is false)")
 	}
 	if !tciDigitalMode(mode) {
-		// Refused rather than attempted. A pass in SSB keys the transmitter,
-		// produces nothing, and teaches nobody anything — and it is still a
-		// transmission.
-		return fmt.Errorf("the radio is in %s: transmit audio over TCI only reaches the modulator in a digital mode (DIGU, DIGL, or an FT8/data mode) — switch mode and try again", mode)
+		// A NOTE, not a refusal.
+		//
+		// The first experiments said "digital modes only": SSB produced nothing
+		// four times over, DIGU answered at once. That was a real observation
+		// and the wrong rule. ExpertSDR3 has a TRANSMIT AUDIO SOURCE — the
+		// microphone or TCI — and it was simply set to the microphone; the mode
+		// had nothing to do with it. Refusing SSB would have blocked the one
+		// thing a voice keyer exists for.
+		debugLog.Printf("TCI: TX PROBE — mode is %s, not a digital mode. That is fine IF ExpertSDR3's transmit audio source is set to TCI rather than the microphone; if it is not, the radio will not ask for audio and this stops straight away", mode)
 	}
 
 	t.audio.mu.Lock()
@@ -206,7 +216,32 @@ func (t *TCI) ProbeTXStream(seconds int, toneHz float64) error {
 		}
 	}()
 
-	time.Sleep(time.Duration(seconds) * time.Second)
+	// Wait for the radio to ask, and give up quickly if it does not.
+	//
+	// The radio declares what it wants by requesting audio — 47 times a second
+	// when it wants any at all. So there is no need to decide in advance whether
+	// this mode or that setting will work: key, listen for one request, and if
+	// none comes in a fifth of a second, stop. That is a quarter of a second of
+	// carrier instead of five, and an answer that names the setting to change.
+	deadline := time.Now().Add(200 * time.Millisecond)
+	for time.Now().Before(deadline) {
+		t.audio.mu.Lock()
+		asked := t.audio.txSent > 0
+		t.audio.mu.Unlock()
+		if asked {
+			break
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	t.audio.mu.Lock()
+	started := t.audio.txSent
+	t.audio.mu.Unlock()
+	if started == 0 {
+		debugLog.Printf("TCI: TX PROBE — the radio never asked for audio; set ExpertSDR3's transmit audio source to TCI (it is on the microphone)")
+		return fmt.Errorf("the radio did not ask for any audio — set ExpertSDR3's transmit audio source to TCI instead of the microphone, then try again")
+	}
+
+	time.Sleep(time.Duration(seconds)*time.Second - 200*time.Millisecond)
 
 	t.audio.mu.Lock()
 	sent, short := t.audio.txSent, t.audio.txShort