diff --git a/internal/antgenius/antgenius.go b/internal/antgenius/antgenius.go
index 43e80a0..072386a 100644
--- a/internal/antgenius/antgenius.go
+++ b/internal/antgenius/antgenius.go
@@ -116,7 +116,11 @@ func (c *Client) Activate(port, antenna int) error {
 	if antenna < 0 {
 		return fmt.Errorf("antgenius: invalid antenna %d", antenna)
 	}
-	if err := c.send(fmt.Sprintf("port set %d rxant=%d txant=%d", port, antenna, antenna)); err != nil {
+	// Set only rxant (like the reference ShackMaster client): the AG mirrors it
+	// to the TX antenna automatically. Forcing txant too can be rejected on the
+	// 8x2 (an antenna can't be TX on both ports at once), which broke port-B
+	// selection and deselection.
+	if err := c.send(fmt.Sprintf("port set %d rxant=%d", port, antenna)); err != nil {
 		return err
 	}
 	// Ask for the new port state so the snapshot reflects it promptly (the